Invasion Biology, Ecology, and Management of Western Flower Thrips

Chromosome-level genome assembly of Dendrothrips minowai and genomic analysis highlights distinct adaptations to high polyphenols in tea plants

BACKGROUND

Dendrothrips minowai Priesner, a significant pest in tea-producing regions of Asia, particularly China, damages tea plants (Camellia sinensis) by feeding on their tender leaves rich in polyphenols. Seven assembled genomes from the order Thysanoptera are currently available.

RESULTS

This study presents the first chromosome-level genome assembly of D. minowai generated by PacBio Revio, Oxford Nanopore Technologies, MGI, and Hi-C technology. The assembled genome measures 350.11 Mb with 1269 contigs with a contig N50 of 536.34 Kb and a scaffold N50 of 16.86 Mb, organized across 19 chromosomes. A total of 16 730 protein-coding genes were identified, with 92.28% functionally annotated. The phylogenetic analysis reveals that D. minowai diverged approximately 103.2 million years ago, preceding all reported genomes of Thripidae species. Comparative genomic analysis identified 12 expanded and 172 contracted gene families of D. minowai, with expanded gene families linked to host plant metabolite processing and detoxification enzymes. Additionally, oligophagous thrips, D. minowai and Stenchaetothrips biformis, possess fewer chemosensory genes (gustatory receptors, odorant receptors, ionotropic receptors, chemosensory proteins, and odorant binding proteins) and detoxification genes (P450s, carboxyl/cholinesterases, UDP-glycosyltransferases) than polyphagous species (Frankliniella occidentalis and Thrips palmi). Interestingly, D. minowai exhibits an expansion in ABC transporter families, especially ABCG and ABCC, which is likely essential for detoxifying the high polyphenol content in tea plants.

CONCLUSION

This study provides another genome sequence for oligophagous thrips species, which enriches the genomic data for further studies on the evolution, host adaptation, and novel control strategies of thrips. © 2025 Society of Chemical Industry.

Artificial lighting affects the predation performance of the Insidiosus flower bug (Hemiptera: Anthocoridae) against the Western flower thrips (Thysanoptera: Thripidae)

Protected crops like greenhouses and indoor farms using light-emitting diodes (LEDs) allow precise control of light spectrum, intensity, and photoperiod for agronomic purposes. These artificial light conditions also influence insects and arachnids, including predators used in biological control. Despite growing interest, the effects of LEDs on predator behavior and control efficacy remain poorly understood. In microcosm experiments, we studied the locomotion and predation behaviors of the generalist predator Orius insidiosus against thrips (Frankliniella occidentalis) under different light spectra and intensities. We tested narrowband blue, green, and red spectra, 3 blue-red ratios, and a spectrum combining all 3 colors across a light-intensity gradient. Predators attacked prey under all lighting conditions, with 70% of individuals showing predatory behavior during observations. Spectral composition significantly influenced behaviors of interest, while light intensity had negligible effects. Narrowband spectra elicited the highest attack probabilities, but the mixed blue-red spectrum with a higher proportion of red light yielded the highest prey capture rates. The spectrum combining all 3 colors showed intermediate prey capture success. In complex environments with cucumber plants and 24-h artificial light sequences, prey capture probabilities followed similar trends to microcosm experiments. However, thrips survival rates remained similar across all lighting treatments. Our findings suggest that while lighting influences O. insidiosus behavior, this predator remains effective under various conditions, providing a foundation for lighting strategies that balance plant productivity with biological control.

Phthorimaea absoluta (Meyrick) (Lepidoptera: Gelechiidae) draft mitogenomes and insecticide resistance gene characterisation support multiple maternal lineages in invasive African, Asian, and European populations

The tomato leafminer, Phthorimaea absoluta (synonym Tuta absoluta Meyrick, 1917), is a transboundary plant pest that poses a serious threat to global tomato cultivation and production, with significant negative social and environmental impact from increased insecticide usage for its management. We present three P. absoluta draft mitochondrial genomes (mitogenomes) from Malawi and South Africa, thereby increasing the mitogenome resources for this invasive agricultural pest. Comparative analysis with Spain, China, and Kenya samples revealed at least seven maternal lineages across its current invasive ranges, supporting multiple introductions as a major factor for the spread of invasive populations. Mitogenome results therefore identified unexpected diversity as compared to the use of the partial mitochondrial cytochrome oxidase subunit I (mtCOI/cox1) gene marker for the inference of P. absoluta invasion biology. The whole-genome sequencing approach further identified alternative mitochondrial DNA (mtDNA) gene regions necessary to improve diversity estimates, and enables concurrent characterisation of insecticide resistance genes. Characterisation of the VSSG (Para) and AChE-1/ace-1 gene profiles that underpin pyrethroid and organophosphate (OP) resistances, respectively, confirmed co-introductions of pyrethroid and OP resistance genes into Malawian and South African populations. Our study highlights the need for additional P. absoluta mitogenome resources, especially from native populations that is needed for more accurate interpretations of introduction pathways and the development of future sustainable management strategies.

The thrips gut pH and implications for symbiont-mediated RNAi

The gut pH plays crucial roles in diet preference, habitat choice, insect fitness, and insect-microbial relationships. It significantly impacts enzyme activity efficiency, as well as the internalisation and efficacy of pesticides. Without a comprehensive understanding of the gut environment, potential pest management strategies cannot be fully optimised.This study investigates the gut pH of the globally invasive pest insect Western flower thrips Frankliniella occidentalis, and the effect its Gram-negative symbiotic gut bacterium BFo2 has on pH modulation. Indicator dyes were fed to F. occidentalis and the gut pH was found to vary between 6 and 7. In general, the larval and adult guts appear to have a pH of between 6 and 6.5; however, the posterior gut of some adults appears to be closer to 7. This almost neutral pH offers a favourable environment for the neutrophilic symbiotic BFo2. The ability of BFo2 isolates to buffer pH towards neutral was also observed during in vitro culture using broths at different pH values.This paper also discusses the implications of this gut environment on dsRNAi delivery. By laying the foundation for understanding how gut pH can be leveraged to enhance current pest management strategies, this study particularly benefits research aimed at optimising the delivery of lethal dsRNA through symbiont-mediated RNAi to Western flower thrips in pest management programs.

Molecular Characterization and Binding Properties of Odorant Binding Protein 7 in Western Flower Thrips, Frankliniella occidentalis (Thysanoptera: Thripidae)

Odorant-binding proteins (OBPs) play a critical role in the olfactory communication systems of insects. Western flower thrips (WFT), Frankliniella occidentalis (Pergande), are devastatingly invasive pests that cause significant damage to a wide range of crops globally. However, there is limited research investigating the functional roles of OBPs in WFT. In this study, we successfully cloned and expressed the recombinant protein FoccOBP7. Fluorescence competition binding assays demonstrated that FoccOBP7 exhibited a high affinity for dibutyl phthalate (DBP) and β-ionone. Three amino acid residues (Q101A, Y112A, and M115A) and two residues (Q101A and Y112A) were essential in influencing the binding affinity of FoccOBP7 to DBP and β-ionone, respectively. DBP could elicit the most significant electroantennogram (EAG) responses among the 11 volatile compounds. Following RNA interference (RNAi), both the EAG response and Y-tube behavioral tropism to DBP were significantly decreased. This study highlighted the importance of FoccOBP7 in mediating olfactory responses and DBP as potential disorienting odorants for pest management strategies in the future.

The role of salivary effector FoCA2 in modulating the interactions of the defense response of the kidney bean plant and the adaptability of Frankliniella occidentalis under dinotefuran exposure

Frankliniella occidentalis (Pergande) is a horticultural pest known for its overwhelming destructive power. Our previous study showed that dinotefuran significantly inhibited the feeding behavior of F. occidentalis on kidney bean plants. However, why dinotefuran suppressed feeding in F. occidentalis is unknown. Here, we analyzed differences in gene expression in the head (containing salivary glands) of F. occidentalis with or without dinotefuran LC25 stress using transcriptome sequencing. Eventually, a salivary protein gene belonging to the carbonic anhydrase (CA) family was obtained and named as FoCA2. The full-length cDNA of FoCA2 was obtained by cloning, and the role of FoCA2 in the F. occidentalis antidefense toward the kidney bean plant was investigated using RNA interference. The results showed that FoCA2 was highly expressed in the head of F. occidentalis and at the feeding stages (nymph and adult). Silencing FoCA2 significantly inhibited F. occidentalis feeding and decreased its fecundity and survival; activated jasmonic and salicylic acid signaling pathway-related genes and callose synthase genes; and induced callose accumulation. However, dinotefuran down-regulated the expression of FoCA2 thereby attenuating the suppression of plant defense responses by FoCA2, which ultimately reduced the adaptability of F. occidentalis. Taken together, our findings suggest that FoCA2 is a key effector protein involved in F. occidentalis feeding and host adaptation, providing a foundation for studying the interaction between F. occidentalis and its host plants, and providing insights into the role of dinotefuran on pests.

Marigold, Tagetes patula, a Trap Plant for Western Flower Thrips, Frankliniella occidentalis, in Ornamental Bedding Plants Under Controlled Greenhouse Conditions

Western flower thrips (WFT), Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae], is a destructive pest of greenhouse ornamentals. Flowering yellow marigolds, Tagetes patula (L.) [Asterales: Asteraceae], have been shown to be attractive to WFT, implicating their suitability as a trap plant. However, functionality may vary in part due to crop variety, the growth stage of the crop in which the marigold trap plant is deployed and whether or not the crop plants have flowers present. The attractiveness of yellow marigolds was tested within several varieties of mature, flowering ornamental bedding plants that were flowering or had their flowers removed: Calibrachoa spp. Petunia spp. Verbena spp., Osteospermum spp., Impatiens haekeri and other marigolds. Trials were conducted in cages under controlled greenhouse conditions for six weeks. The effectiveness of orange vs. yellow marigolds as a trap plant was also assessed. The results showed that WFT were attracted to flowering marigolds and, over time, were present in greater numbers on these than crop plants for all crop species and varieties tested at varying levels of significance. Yellow marigold trap plants were the least effective when deployed within other marigold varieties. In crops with flowers, it took up to five weeks for the number of WFT on trap plants to surpass numbers on crop plants. In contrast, in crop varieties with their flowers removed, trap plants attracted WFT earlier, within one to two weeks, and harbored them in greater numbers over time. Orange, flowering marigolds were a less effective trap plant compared to yellow marigolds. These results confirm that flowering yellow marigolds are attractive to WFT and have potential as a trap plant in greenhouse ornamentals, particularly when crop plants do not have flowers.

A Computational Analysis Based on Automatic Digitization of Movement Tracks Reveals the Altered Diurnal Behavior of the Western Flower Thrips, Frankliniella occidentalis, Suppressed in PKG Expression

The western flower thrips, Frankliniella occidentalis, a worldwide insect pest with its polyphagous feeding behavior and capacity to transmit viruses, follows a diurnal rhythmicity driven by expression of the circadian clock genes. However, it remained unclear how the clock signal triggers the thrips behaviors. This study posed a hypothesis that the clock signal modulates cGMP-dependent protein kinase (PKG) activity to mediate the diurnal behaviors. A PKG gene is encoded in F. occidentalis and exhibits high sequence homologies with those of honeybee and fruit fly. Interestingly, its expression followed a diel pattern with high expression during photophase in larvae and adults of F. occidentalis. It is noteworthy that PKG expression was clearly observed in the midgut during photophase but not in scotophase from our fluorescence in situ hybridization analysis. A prediction of protein-protein interaction suggested its functional association with clock genes. To test this functional link, RNA interference (RNAi) of the PKG gene expression was performed by feeding a gene-specific double-stranded RNA, which led to significant alteration of the two clock genes (Clock and Period) in their expression levels. The RNAi treatment caused adverse effects on early-life development and adult fecundity. To further analyze the role of PKG in affecting diurnal behavior, the adult females were continuously observed for a 24 h period with an automatic digitization device to obtain movement parameters and durations (%) in different micro-areas in the observation arena. Diel difference was observed with speed in RNAi-control females at 0.16 mm/s and 0.08 mm/s, in photo- and scotophase, respectively, whereas diel difference was not observed for the PKG-specific RNAi-treated females, which showed 0.07 mm/s and 0.06 mm/s, respectively. The diel difference was also observed in durations (%) in the control females, more strongly in the intermediate area in the observation arena. Speed and durations in the different micro-areas in mid-scotophase were significantly different from most photophase in the control females, while speed was significantly different mainly during late photophase when comparing effects of control and RNAi treatments in each light phase. Three sequential stages consisting of high activity followed by feeding and visiting of micro-areas were observed for the control females. For RNAi-treated females, the three phases were disturbed with irregular speed and visits to micro-areas. These results suggest that PKG is associated with implementing the diurnal behavior of F. occidentalis by interacting with expressions of the circadian clock genes.

Ecological risks of a biopesticide from marine-derived amino-oligosaccharides in agriculture: Food chain effects on non-target organisms Frankliniella occidentalis and its natural predator Neoseiulus barkeri

A biopesticide from marine-derived amino-oligosaccharides (AO) are extensively utilized in China, yet there is a lack of scientific literature on their potential ecological risks when transmitted through the food chain to Neoseiulus barkeri, a natural predator of Frankliniella occidentalis. In this study, we conducted a comprehensive investigation into the food chain effects of AO on both F. occidentalis and N. barkeri. Our findings indicate that AO-treated cucumber leaves facilitated the population growth of F. occidentalis but indirectly suppressed the fecundity of N. barkeri which fed on the first instar nymphs of F. occidentalis. Besides, F. occidentalis that ingested AO-treated cucumber leaves exhibited elevated levels of total protein and defense enzymes, including catalase (CAT) and peroxidase (POD), whereas the detoxification enzymes activity, such as carboxylesterase (CarE) and cytochrome P450 monooxygenase (P450), was diminished. Conversely, N. barkeri exhibited decreased levels of the defense enzymes superoxide dismutase (SOD) and POD, coupled with an elevated CarE activity, because of AO food chain transmission. In conclusion, the food chain effects of AO on non-target organisms F. occidentalis and N. barkeri may involve the modulation of defense and detoxification enzyme activities, leading to varying fitness costs. These findings provide critical insights for agricultural pest management strategies, highlighting the necessity of evaluating the effects of AO on non-target organisms within ecosystems, especially beneficial insects, during its application.

Influence of different diet categories on gut bacterial diversity in Frankliniella occidentalis

The microbial composition of insect guts is typically influenced by the type of food consumed, and conversely, these microbes influence the food habits of insects. Western flower thrips (WFT; Frankliniella occidentalis) is an invasive pest with a wide range of hosts, including vegetables and horticultural crops. To elucidate variations in gut bacteria among WFT feeding on rose (Rosa rugosa) flowers (FF), kidney bean (Phaseolus vulgaris) pods (PF), and kidney bean leaves (LF), we collected adult guts and extracted DNA for 16S ribosomal RNA gene sequencing of microbial communities. The results revealed that the FF population had the highest number of annotations. Alpha diversity analysis revealed that the Chao and Ace indexes were the greatest in the PF population, indicating a higher abundance of gut bacteria. Moreover, the Simpson index was the highest in the FF population, indicating that gut bacterial diversity was the highest in the FF population. Comparison of species composition demonstrated that Proteobacteria dominated all 3 populations at the phylum level, with Actinobacteria being the subdominant phylum. At the genus level, Stenotrophomonas was the dominant bacteria in the PF and LF populations, whereas Rosenbergiella was dominant in the FF population. KEGG pathway annotation predicted that the gut bacteria of adult WFT were mainly involved in carbohydrate and amino acid metabolism. Our results revealed that the diversity and composition of WFT gut microbiota are influenced by diet, offering evidence for future studies on the ecological adaptability of WFT and the mechanisms underlying the interaction between gut microbiota and host.

Eavesdropping the pivotal defensive representatives of plant-thrips interaction

The substantial economic impact of thrips on crop yield and productivity enthused us to review comprehensive research findings associated with plant-thrips interaction. An attempt has been made to summarize a broad spectrum of knowledge on thrips infestation in different crops regarding defensive traits including plant morphological features, biochemical alterations and transcriptional profiling of defensive genes along with effective thrips management strategies. Thrips feeding mechanism involves puncturing the outer (epidermal) layer of host tissue and evoking the plant defence mechanism. Plants respond to thrips attacks by activating the defensive genes, which lead to the production of physical barriers (trichomes, waxes, and papillae) and biochemical compounds (primary and secondary metabolites). It is imperative to appreciate the physiological responses, metabolic changes, and regulation at the transcriptional level of various phytoconstituents during thrips feeding. The literature survey revealed that leaf size, papillae and trichome density, total phenols, tannins and genes associated with phenylalanine metabolism and flavonoid biosynthesis contribute to plant resistance against thrips infestation. Thus, this comprehensive overview will serve as a roadmap for researchers, guiding future studies and the development of sustainable pest management practices to mitigate thrips-related damage and enhance crop resilience.

Spraying calcium chloride helps to enhance the resistance of kidney bean plants to western flower thrips

BACKGROUND

The western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae), is a significant pest in horticulture and ornamental agriculture. While exogenous calcium (Ca) has been shown to confer plant immune responses against thrips, the detailed mechanisms of this interaction remain to be elucidated for improved thrips management strategies. This study aimed to assess the impact of exogenous Ca on WFT feeding behavior and to explore its role in enhancing the defense mechanisms of kidney bean plants against WFT attacks. We compared WFT feeding preferences and efficiency on kidney bean plants treated with H2O or Ca, and examined whether exogenous Ca improves plant defense responses to thrips attack.

RESULTS

WFT exhibited less preference for feeding on Ca-treated plants over H2O-treated ones. The total duration of WFT's long-ingestion probes was significantly reduced on Ca-treated plants, indicating impaired feeding efficiency. Furthermore, WFT infestation activated both jasmonic acid (JA) and salicylic acid (SA) signaling pathways in kidney bean plants, and exogenous Ca application led to elevated levels of endogenous Ca2+ and CaM, up-regulation of genes associated with JA and SA pathways (LOX, AOS, PAL, and β-1,3-glucanase), and increased accumulation of JA, SA, flavonoids, and alkaloids.

CONCLUSION

Our findings demonstrate that the application of exogenous Ca enhances endogenous Ca2+, JA, and SA signaling pathways in kidney bean plants. This enhancement results in an up-regulation of the biosynthesis of flavonoid and alkaloid, thereby equipping the plants with an enhanced defense against WFT infestation. © 2024 Society of Chemical Industry.

CRISPR/Cas9-mediated genome editing of Frankliniella occidentalis, the western flower thrips, via embryonic microinjection

The western flower thrips, Frankliniella occidentalis, poses a significant challenge in global agriculture as a notorious pest and a vector of economically significant orthotospoviruses. However, the limited availability of genetic tools for F. occidentalis hampers the advancement of functional genomics and the development of innovative pest control strategies. In this study, we present a robust methodology for generating heritable mutations in F. occidentalis using the CRISPR/Cas9 genome editing system. Two eye-colour genes, white (Fo-w) and cinnabar (Fo-cn), frequently used to assess Cas9 function in insects were identified in the F. occidentalis genome and targeted for knockout through embryonic microinjection of Cas9 complexed with Fo-w or Fo-cn specific guide RNAs. Homozygous Fo-w and Fo-cn knockout lines were established by crossing mutant females and males. The Fo-w knockout line revealed an age-dependent modification of eye-colour phenotype. Specifically, while young larvae exhibit orange-coloured eyes, the colour transitions to bright red as they age. Unexpectedly, loss of Fo-w function also altered body colour, with Fo-w mutants having a lighter coloured body than wild type, suggesting a dual role for Fo-w in thrips. In contrast, individuals from the Fo-cn knockout line consistently displayed bright red eyes throughout all life stages. Molecular analyses validated precise editing of both target genes. This study offers a powerful tool to investigate thrips gene function and paves the way for the development of genetic technologies for population suppression and/or population replacement as a means of mitigating virus transmission by this vector.

Transfer and biological effects of cadmium along a tomato - thrip - predatory bug food chain

The heavy metal, cadmium (Cd) is an increasingly serious issue in agricultural ecosystems, mediating bottom-up effects on plants, herbivores and natural enemies. We measured how Cd modifies interactions between tomato Solanum lycopersicum, western flower thrips Frankliniella occidentalis, and the predatory bug Orius sauteri by examining Cd effects on the growth of tomato, the fitness of western flower thrips, and the survival and behavior of predators. The photosynthetic parameters of Pn (net photosynthetic rate), Gs (stomatal conductance), Ci (intercellular CO2 concentration), and Tr (transpiration rate) of tomato plants significantly decreased with the increase of Cd concentration. The total survival number of western flower thrips fed on tomato plants treated with different concentrations of Cd was significantly lower than that of the control, and sex ratios (female/male) gradually increased with the increase of Cd concentration. The numbers of thrips predated by O. sauteri on tomato plants treated with high concentrations of Cd (2.0 or 4.0 mg/L) were significantly reduced by the second day. Cadmium was accumulated and bioconcentrated in the roots, stems, leaves of tomato plants, and transferred to F. occidentalis, and O. sauteri. Cadmium translocated in significant quantities from roots to the stems and leaves of tomato plants, and from the tomato leaf to F. occidentalis. However, there was minimal (non-significant) transfer of Cd from F. occidentalis to O. sauteri. The presence of Cd significantly reduced the growth of tomato plants, the fitness of F. occidentalis, and the predation efficiency of O. sauteri. Collectively, Cd can mediate bottom-up effects on tomato, thrip, and predatory bug along food chain, potentially interrupting pest biological control in tomato in heavy metal-contaminated ecosystems.

Asymmetric Synthesis and Biological Activity of Contact Pheromone of Western Flower Thrips, Frankliniella occidentalis

Western flower thrips, Frankliniella occidentalis, is a serious worldwide pest of agriculture and horticulture, and its contact pheromone is 7-methyltricosane. Two enantiomers of 7-methyltricosane were synthesized for the first time. The centra of our strategy were chiral auxiliaries to introduce stereocenter, and Wittig coupling to connect two blocks. The overall yields of our synthesis were 29-30% with seven steps. The electroantennogram (EAG) and the contact behavioral responses revealed that (R)-, (S)- and racemic 7-methyltricosane were separately bioactive, and the racemate was the most bioactive in the male arrestant activity and the female EAG test. This result provides valuable insights, showing that the racemate could be used for the support of the control of western flower thrips, which could be more easily prepared relative to more expensive enantiopure pheromone.

Rapid detection of Impatiens necrotic spot virus from thrips vectors using reverse transcription-recombinase polymerase amplification

The plant virus, Impatiens necrotic spot virus (INSV), is an economically important pathogen of vegetables, fruits, and ornamental crops. INSV is vectored by the western flower thrips, Frankliniella occidentalis, a small insect pest that is globally distributed. In recent years, INSV outbreaks have reached epidemic levels in the Salinas Valley of California-an agriculturally rich region where most of the lettuce (Lactuca sativa) is produced in the United States. Due to the obligate nature in which virus transmission occurs, new tools that could rapidly detect INSV from thrips vectors would enhance our ability to predict where virus outbreaks may occur. Here, we report on the development of a reverse transcription-recombinase polymerase amplification (RT-RPA) assay that can detect INSV from individual thrips. The assay uses crude extraction methods, is performed at a single temperature of 42 °C, can be completed in 25 min, and provides sensitivity levels that are comparable to other available detection methods. When the assay was used on field populations of thrips, INSV was successfully identified and quantified from individual larvae and adults. The work provides a new cost-effective surveillance tool that can rapidly detect INSV from its insect vector and from plants.

Suppression of Thrips palmi population by spray-on application of dsRNA targeting V-ATPase-B

The RNA interference (RNAi)-based gene silencing technique has enormous potential as a non-chemical and eco-friendly alternative to hazardous pesticides. This study reports a spray-induced gene silencing (SIGS) approach for managing Thrips palmi by lowering survival and offspring development. Vacuolar ATP synthases (V-ATPases) are responsible for survival, egg-laying, and viability of eggs in insects. In the current study, T. palmi V-ATPase-B was targeted to suppress the pest population by spray-on application of double-stranded RNA (dsRNA). Silencing of V-ATPase-B was first validated by oral administration of dsV-ATPase-B. The expression of V-ATPase-B was reduced by 5.40-fold post-dsRNA feeding leading to increased mortality (57.03 %) and reduced reproductive fitness (67.73 %). Spray-on application of naked dsV-ATPase-B at concentrations of 3.0 μg/mL and 5.0 μg/mL effectively suppressed the population by 30.00 % and 43.33 %, respectively. The expression of the target gene was downregulated by up to 4.24-fold. Two consecutive sprays at a concentration of 5.0 μg/mL provided substantial protection against the fresh release of T. palmi for up to 10 days. The spray-on application of dsV-ATPase-B would be an eco-friendly alternative for managing T. palmi populations thereby reducing crop damage and limiting the spread of orthotospoviruses.

MCMV-infected maize attracts its insect vector Frankliniella occidentalis by inducing β-myrcene

Maize lethal necrosis is attributed to the accumulation of maize chlorotic mottle virus (MCMV), an invasive virus transmitted by insect vectors. The western flower thrips (WFT) can shift host to maize, thus promoting the spread of MCMV. However, our understanding of the characteristics and interactions involved in the transmission of MCMV is still limited. This study finds that non-viruliferous WFTs showed a 57.56% higher preference for MCMV-infected maize plants compared to healthy maize plants, while viruliferous WFTs showed a 53.70% higher preference for healthy maize plants compared to MCMV-infected maize plants. We also show for the first time that both adults and larvae of WFT could successfully acquire MCMV after 1 min of acquisition access period (AAP), and after 48 h of AAP, WFT could transmit MCMV in an inoculation access period of 1 h without a latent period. Both adults and larvae of WFT can transmit MCMV for up to 2 days. Furthermore, the decreasing number of viruliferous WFTs and transmission rates as time progressed, together with the transcriptomic evidence, collectively suggest that WFTs transmit MCMV in a semi-persistent method, a mode of transmission requiring minutes to several hours for acquisition access and having a retention time of several hours to a few days. Additionally, β-myrcene can attract WFTs significantly and is detected in Nicotiana benthamiana plants transiently expressing MCMV CP (coat protein), which is consistent with results in MCMV-infected maize plants through the metabolomic profiling and the preference analyses of WFT. Therefore, this study demonstrates the indirect interaction between MCMV and WFT by inducing maize to synthesize β-myrcene to attract insect vectors. The exploration of specific interactions between MCMV and WFT could help to expand the mechanism studies of virus-vector-host plant interaction and put forward a new insight for the combined control of MCMV and WFT through the manipulation of plant volatiles and key insect genes.

Study on plant protection unmanned aerial vehicle spraying technology based on the thrips population activity patterns during the cotton flowering period

Over the years, thrips have transitioned from a minor nuisance to a major problem, significantly impacting the yield and quality of cotton. Unmanned aerial vehicles (UAVs) for plant protection have emerged as an effective alternative to traditional pesticide spraying equipment. UAVs offer advantages such as avoiding crop damage and enhancing pesticide deposition on the plants and have become the primary choice for pesticide application in cotton fields. In this study, a 2-year field experiment found that the thrips population in a cotton field in Xinjiang, China, exhibited gradual growth during the early flowering phase, peaking in late July. The thrips population gradually shifted from the lower canopy to the upper canopy as the cotton flowers opened layer by layer. From 09:00 to 11:00 (GMT+8) and 19:00 to 21:00 (GMT+8), thrips mainly flew outside the flowers, while from 17:00 to 19:00 (GMT+8), they mostly inhabited the inner whorls of flowers. The insecticides 10% cyantraniliprole oil dispersion and 10% spinetoram suspension concentrate, sprayed by UAV, had the best control effect on thrips, with 80.51% and 79.22% control effect after 7 days of spraying, respectively. The optimal spraying time for 10% cyantraniliprole oil dispersion was 19:00 (GMT+8), and the control effect on thrips reached 91.16% at 7 days of spraying. During the cotton flowering period, thrips inhabited flowers in the evening and flew outside during the day. The best control effect on thrips was achieved with UAV-sprayed 10% cyantraniliprole oil dispersion at 19:00 (GMT+8).

Dehydration and tomato spotted wilt virus infection combine to alter feeding and survival parameters for the western flower thrips, Frankliniella occidentalis

Dehydration and tomato spotted wilt virus (TSWV) infection substantially impact the feeding of western flower thrips, Frankliniella occidentalis. Until now, the dynamics between these biotic and abiotic stresses have not been examined for thrips. Here, we report water balance characteristics and changes in other biological parameters during infection with TSWV for the western flower thrips. There were no apparent differences in water balance parameters during TSWV infection of male or female thrips. Our results show that, although water balance characteristics of western flower thrips are minimally impacted by TSWV infection, the increase in feeding and activity when dehydration and TSWV are combined suggests that virus transmission could be increased under periods of drought. Importantly, survival and progeny generation were impaired during TSWV infection and dehydration bouts. The negative impact on survival and reproduction suggests that the interactions between TSWV infection and dehydration will likely reduce thrips populations. The opposite effects of dehydration on feeding/activity and survival/reproduction for virus infected thrips suggest the impact of vectorial capacity will likely be minor for TSWV transmission. As water stress significantly impacts insect-plant-virus dynamics, these studies highlight that all interactions and effects need to be measured to understand thrips-TSWV interactions in their role as viral vector to plants.

Chromosome-level genome assembly of the western flower thrips Frankliniella occidentalis

The western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae) is a global invasive species that causes increasing damage by direct feeding on crops and transmission of plant viruses. Here, we assemble a previously published scaffold-level genome into a chromosomal level using Hi-C sequencing technology. The assembled genome has a size of 302.58 Mb, with a contig N50 of 1533 bp, scaffold N50 of 19.071 Mb, and BUSCO completeness of 97.8%. All contigs are anchored on 15 chromosomes. A total of 16,312 protein-coding genes are annotated in the genome with a BUSCO completeness of 95.2%. The genome contains 492 non-coding RNA, and 0.41% of interspersed repeats. In conclusion, this high-quality genome provides a convenient and high-quality resource for understanding the ecology, genetics, and evolution of thrips.

Leveraging insect viruses and genetic manipulation for sustainable agricultural pest control

The potential of insect viruses in the biological control of agricultural pests is well-recognized, yet their practical application faces obstacles such as host specificity, variable virulence, and resource scarcity. High-throughput sequencing (HTS) technologies have significantly advanced our capabilities in discovering and identifying new insect viruses, thereby enriching the arsenal for pest management. Concurrently, progress in reverse genetics has facilitated the development of versatile viral expression vectors. These vectors have enhanced the specificity and effectiveness of insect viruses in targeting specific pests, offering a more precise approach to pest control. This review provides a comprehensive examination of the methodologies employed in the identification of insect viruses using HTS. Additionally, it explores the domain of genetically modified insect viruses and their associated challenges in pest management. The adoption of these cutting-edge approaches holds great promise for developing environmentally sustainable and effective pest control solutions. © 2023 Society of Chemical Industry.

Four phospholipase A2 genes encoded in the western flower thrips genome and their functional differentiation in mediating development and immunity

Eicosanoids are synthesized from phospholipids by the catalytic activity of phospholipase A2 (PLA2). Even though several PLA2s are encoded in the genome of different insect species, their physiological functions are not clearly discriminated. This study identified four PLA2 genes encoded in the western flower thrips, Frankliniella occidentalis. Two PLA2s (Fo-PLA2C and Fo-PLA2D) are predicted to be secretory while the other two PLA2s (Fo-PLA2A and Fo-PLA2B) are intracellular. All four PLA2 genes were expressed in all developmental stages, of which Fo-PLA2B and Fo-PLA2C were highly expressed in larvae while Fo-PLA2A and Fo-PLA2D were highly expressed in adults. Their expressions in different tissues were also detected by fluorescence in situ hybridization. All four PLA2s were detected in the larval and adult intestines and the ovary. Feeding double-stranded RNAs specific to the PLA2 genes specifically suppressed the target transcript levels. Individual RNA interference (RNAi) treatments led to significant developmental retardation, especially in the treatments specific to Fo-PLA2B and Fo-PLA2D. The RNAi treatments also showed that Fo-PLA2B and Fo-PLA2C expressions were required for the induction of immune-associated genes, while Fo-PLA2A and Fo-PLA2D expressions were required for ovary development. These results suggest that four PLA2s are associated with different physiological processes by their unique catalytic activities and expression patterns.

Mutation V65I in the β1 Subunit of the Nicotinic Acetylcholine Receptor Confers Neonicotinoid and Sulfoxaflor Resistance in Insects

Neonicotinoids have been widely used to control pests with remarkable effectiveness. Excessive insecticides have led to serious insect resistance. Mutations of the nicotinic acetylcholine receptor (nAChR) are one of the reasons for neonicotinoid resistance conferred in various agricultural pests. Two mutations, V65I and V104I, were found in the nAChR β1 subunit of two neonicotinoid-resistant aphid populations. However, the specific functions of the two mutations remain unclear. In this study, we cloned and identified four nAChR subunits (α1, α2, α8, and β1) of thrips and found them to be highly homologous to the nAChR subunits of other insects. Subsequently, we successfully expressed two subtypes nAChR (α1/α2/α8/β1 and α1/α8/β1) by coinjecting three cofactors for the first time in thrips, and α1/α8/β1 showed abundant current rapidly. Acetylcholine, neonicotinoids, and sulfoxaflor exhibited different activation capacities for the two subtypes of nAChRs. Finally, V65I was found to significantly reduce the binding ability of nAChR to neonicotinoids and sulfoxaflor through electrophysiology and computer simulations. V104I caused a decrease in agonist affinity (pEC50) but an increase in the efficacy (Imax) of nAChR against neonicotinoids and reduced the binding ability of nAChR to sulfoxaflor. This study provides theoretical and technical support for studying the molecular mechanisms of neonicotinoid resistance in pests.

A chromosome-level genome for the flower thrips Frankliniella intonsa

The flower thrips Frankliniella intonsa (Thysanoptera: Thripidae) is a common insect found in flowers of many plants. Sometimes, F. intonsa causes damage to crops through direct feeding and transmission of plant viruses. Here, we assembled a chromosomal level genome of F. intonsa using the Illumina, Oxford Nanopore (ONT), and Hi-C technologies. The assembled genome had a size of 209.09 Mb, with a contig N50 of 997 bp, scaffold N50 of 13.415 Mb, and BUSCO completeness of 92.5%. The assembled contigs were anchored on 15 chromosomes. A set of 14,109 protein-coding genes were annotated in the genome with a BUSCO completeness of 95.0%. The genome contained 491 non-coding RNA and 0.57% of interspersed repeats. This high-quality genome provides a valuable resource for understanding the ecology, genetics, and evolution of F. intonsa, as well as for controlling thrips pests.

The inappropriate application of imidacloprid destroys the ability of predatory natural enemies to control pests in the food chain: A case study of the feeding behavior of Orius similis on Frankliniella occidentalis

Insecticides are an indispensable and important tool for agricultural production. However, the inappropriate application of insecticides can cause damage to the food chain and ecosystem. Orius similis is an important predatory and natural enemy of Frankliniella occidentalis. Imidacloprid is widely used to control pests, but will inevitably exert adverse effects on O. similis. In order to determine the effect of different imidacloprid treatments on the ability of O. similis to prey on the 2nd-instar nymphs of F. occidentalis, we determined the toxicity and predation of imidacloprid on different stages of O. similis under contact and ingestion treatments. In addition, we used the Holling disc equation to evaluate the ability of O. similis to search and exhibit predatory activity following contact and ingestion treatments. Analysis showed that the highest LC10 and LC20 values for imidacloprid contact and ingestion toxicity treatment were 17.06 mg/L and 23.74 mg/L, respectively. Both imidacloprid treatments led toa reduction in the predatory of O. similis on prey. The functional responses of the 3rd to 5th instar nymphs, along with female and male O. similis adults to the 2nd-instar nymphs of F. occidentalis were consistent with the Holling type II response following contact and ingestion with imidacloprid. However, following imidacloprid treatment, the handing time (Th) of O. similis with single F. occidentalis was prolonged and the instantaneous attack rate (a) was reduced after imidacloprid treatment. The predatory capacity (a/Th) of female O. similis adults when treated with the LC10 concentration of imidacloprid by ingestion was 52.85; this was lower than that of the LC10 concentration of imidacloprid in the contact treatment (57.67). The extent of predation of O. similis on the 2nd-instar nymphs of F. occidentalis was positively correlated with prey density, although the search effect was negatively correlated with prey density. The most extensive search effect was exhibited by adult O. similis females. Simulations with the Hessell-Varley interference model showed that an increase in the number of O. similis would reduce search efficiency regardless of whether they were treated with imidacloprid or not. Thus, O. similis, especially female adults, exhibited strong potential for controlling the 2nd-instar nymphs of F. occidentalis. The toxicity of ingestion following treatment with the same concentration of imidacloprid in O. similis was greater than that of contact treatment. When using O. similis to control F. occidentalis in the field, we should increase the number of female adults released, and prolong the interval between imidacloprid treatment and O. similis exposure. This strategy will improve the control ability of O. similis, coordinate both chemical and biological control, reduce the impact of pesticides on the environment, and improve the efficiency of agricultural production.

Genome-wide identification of cuticle protein superfamily in Frankliniella occidentalis provide insight into the control of both insect vectors and plant virus

The structural cuticle proteins (CPs) play important roles in the development and fitness of insects. However, knowledge about CP gene superfamily is limited in virus-transmitting insect vectors, although its importance on transmission of plant virus has been gradually emphasized. In this study, the genome-wide identification of CP superfamily was conducted in western flower thrips Frankliniella occidentalis that is the globally invasive pest and plant virus vector pest. The pest transmits notorious tomato spotted wilt virus (TSWV) around the world, causing large damage to a wide array of plants. One hundred and twenty-eight F. occidentalis CP genes (FoCPs) were annotated in this study and they were classified into 10 distinct families, including 68 CPRs, 16 CPAP1s, 6 CPAP3s, 2 CPCFCs, 10 Tweedles, 4 CPFs, 16 CPLCPs, and 6 CPGs. The comprehensive analysis was performed including phylogenetic relationship, gene location and gene expression profiles during different development stages of F. occidentalis. Transcriptome analysis revealed more than 30% FoCPs were upregulated at least 1.5-fold when F. occidentalis was infected by TSWV, indicating their potential involvement in TSWV interactions. Our study provided an overview of F. occidentalis CP superfamily. The study gave a better understand of CP's role in development and virus transmission, which provided clues for reducing viral damages through silencing CP genes in insect vectors.

Identification of the odorant binding proteins of Western Flower Thrips (Frankliniella occidentalis), characterization and binding analysis of FoccOBP3 with molecular modelling, molecular dynamics simulations and a confirmatory field trial

Olfactory systems are indispensable for insects as they, including Western Flower Thrips (Frankliniella occidentalis), use olfactory cues for ovipositing and feeding. F. occidentalis use odorant binding proteins (OBPs) to transport semiochemicals to odorant receptors to induce a behavioural response from the sensillum lymph of the insect's antennae. This study identifies four OBPs of F. occidentalis and analyses their expression at three stages of growth: larvae, adult males and adult females. Further, it investigates the presence of conserved motifs and their phylogenetic relationship to other insect species. Moreover, FoccOBP3 was in silico characterized to analyse its structure along with molecular docking and molecular dynamics simulations to understand its binding with semiochemicals of F. occidentalis. Molecular docking revealed the interactions of methyl isonicotinate, p-anisaldehyde and (S)-(-)-verbenone with FoccOBP3. Moreover, molecular dynamics simulations showed bonding stability of these ligands with FoccOBP3, and field trials validated that Lurem TR (commercial product) and p-anisaldehyde had greater attraction as compared to (S)-(-)-verbenone, given the compound's binding with FoccOBP3. The current study helps in understanding the tertiary structure and interaction of FoccOBP3 with lures using computational and field data and will help in the identification of novel lures of insects in the future, given the importance of binding with OBPs.

Visual stimulus brightness influences the efficiency of attractant-baited traps for catching Drosophila suzukii Matsumura (Diptera: Drosophilidae)

Drosophila suzukii (Matsumura) is an exotic pest of economic importance that affects several soft-skinned fruits in Mexico. Previously, we found that yellow or yellow-green rectangular cards inside a transparent trap baited with attractants improved D. suzukii capture. In this study, we evaluated the influence of rectangular cards with different yellow shades inside a transparent multi-hole trap baited with apple cider vinegar (ACV) on D. suzukii capture in the field. Second, we tested whether ACV-baited traps with cards of other geometric shapes affected D. suzukii catches compared to traps with rectangular cards. Third, we evaluated the effects of commercial lures combined with a more efficient visual stimulus from previous experiments on trapping D. suzukii flies. We found that ACV-baited traps plus a yellow-shaded rectangle card with 67% reflectance at a 549.74 nm dominant wavelength captured more flies than ACV-baited traps with yellow rectangle cards with a higher reflectance. Overall, ACV-baited traps with rectangles and squares caught more flies than did ACV-baited traps without visual stimuli. The traps baited with SuzukiiLURE-Max, ACV and Z-Kinol plus yellow rectangles caught 57, 70 and 101% more flies, respectively, than the traps baited with the lure but without a visual stimulus.

Nitrogen Deficiency Enhances Eggplant Defense against Western Flower Thrips via the Induction of the Jasmonate Pathway

Plant nutrition is connected to defense against insect herbivores, but the exact mechanism underlying the effect of the nitrogen (N) supply on the anti-herbivore capacity of eggplants (Solanum melongena) has not been studied in detail. Therefore, we examined the impact of low (LN, 0.5 mM) and high (HN, 5 mM) nitrate levels on eggplant resistance against the western flower thrips Frankliniella occidentalis (WFT), a major destructive eggplant pest. Our results showed that LN plants displayed enhanced defense responses to WFT compared to HN plants. This included increased transcript levels of key genes in the jasmonic acid (JA) pathway, the accumulation of JA-amido conjugates (jasmonoyl-isoleucine, jasmonoyl-phenylalanine, and jasmonoyl-valine), JA precursor (12-oxophytodienoic acid), and methyl jasmonate, higher transcript levels of defense marker genes (MPK3, MPK7, and WRKY53), and increased activities of polyphenol oxidase and peroxidase upon a WFT attack. Our findings suggest that N deficiency can prime JA-mediated defense responses in eggplants, resulting in increased anti-herbivore resistance.

Integration of the Generalist Predator Nabis americoferus (Hemiptera: Nabidae) in a Greenhouse Strawberry Biocontrol Program with Phytoseiid Predatory Mites and the Entomopathogenic Fungus Beauveria bassiana

In strawberry production, western flower thrips (WFT) and two-spotted spider mites (TSSM) inflict feeding damage and reduce the yield. Biological control for these pests often includes phytoseiid predatory mites and entomopathogenic fungi. The hemipteran family Nabidae have been reported as prominent predators in open-field strawberry. Nabis americoferus Carayon is a new biocontrol agent developed in Canada. This study examined if this species was a good candidate for integration with biological control for greenhouse strawberry production. The laboratory trials showed that Phytoseiulus persimilis Athias-Henriot and Amblyseius swirskii Athias-Henriot were compatible with N. americoferus, especially when alternative food was available. In contrast, the nabid was not compatible with the Beauveria bassiana (Balsamo) GHA strain. A greenhouse cage study was conducted to determine if it was beneficial to add N. americoferus to the phytoseiid-mites-based biological control program for WFT and TSSM in greenhouse strawberry. The release of N. americoferus on a banker plant together with the placement of sachets of Neoseiulus cucumeris (Oudemans) and Neoseiulus californicus (McGregor) was beneficial, not only potentially reducing the number of sachet applications, but also providing better pest control than phytoseiid mites alone. Neither the phytoseiids nor the N. americoferus numbers were significantly affected by the presence of each other.

Efficacy of Conventional and Biorational Insecticides against the Invasive Pest Thrips parvispinus (Thysanoptera: Thripidae) under Containment Conditions

In 2020, the invasive Thrips parvispinus (Karny) was first detected in Florida, United States. In response to the implemented regulatory restrictions, we conducted laboratory experiments under containment conditions. Thrips larvae and adults were exposed to 32 products (conventional and biorational insecticides) either directly or indirectly. Direct exposure was performed using a Spray Potter Tower, while indirect exposure was conducted by evaluating residue toxicity against the thrips. Water served as a control. We assessed mortality and leaf-feeding damage 48 h post-treatment. Among the conventional insecticides, chlorfenapyr, sulfoxaflor-spinetoram, and spinosad caused high mortality across all stages in both direct and residue toxicity assays. Pyridalyl, acetamiprid, tolfenpyrad, cyclaniliprole-flonicamid, acephate, novaluron, abamectin, cyantraniliprole, imidacloprid, cyclaniliprole, spirotetramat, and carbaryl displayed moderate toxicity, affecting at least two stages in either exposure route. Additionally, chlorfenapyr, spinosad, sulfoxaflor-spinetoram, pyridalyl, acetamiprid, cyclaniliprole, cyclaniliprole-flonicamid, abamectin, and acephate inhibited larvae and adult's leaf-feeding damage in both direct and residue toxicity assays. Regarding biorational insecticides, mineral oil (3%) and sesame oil caused the highest mortality and lowest leaf-feeding damage. Greenhouse evaluations of spinosad, chlorfenapyr, sulfoxaflor-spinetoram, and pyridalyl are recommended. Also, a rotation program incorporating these products, while considering different modes of action, is advised for ornamental growers to avoid resistance and to comply with regulations.

Insights into the genetic variability and evolutionary dynamics of tomato spotted wilt orthotospovirus in China

BACKGROUND

Viral diseases are posing threat to annual production and quality of tobacco in China. Recently, tomato spotted wilt orthotospovirus (TSWV) has been reported to infect three major crops including tobacco. Current study was aimed to investigate the population dynamics and molecular diversity of the TSWV. In the current study, to assess and identify the prevalence and evolutionary history of TSWV in tobacco crops in China, full-length genome sequences of TSWV isolates from tobacco, were identified and analyzed.

METHODS

After trimming and validation, sequences of new isolates were submitted to GenBank. We identified the full-length genomes of ten TSWV isolates, infecting tobacco plants from various regions of China. Besides these, six isolates were partially sequenced. Phylogenetic analysis was performed to assess the relativeness of newly identified sequences and corresponding sequences from GenBank. Recombination and population dynamics analysis was performed using RDP4, RAT, and statistical estimation. Reassortment analysis was performed using MegaX software.

RESULTS

Phylogenetic analysis of 41 newly identified sequences, depicted that the majority of the Chinese isolates have separate placement in the tree. RDP4 software predicted that RNA M of newly reported isolate YNKM-2 had a recombinant region spanning from 3111 to 3811 bp. The indication of parental sequences (YNKMXD and YNHHKY) from newly identified isolates, revealed the conservation of local TSWV population. Genetic diversity and population dynamics analysis also support the same trend. RNA M was highlighted to be more capable of mutating or evolving as revealed by data obtained from RDP4, RAT, population dynamics, and phylogenetic analyses. Reassortment analysis revealed that it might have happened in L segment of TSWV isolate YNKMXD (reported herein).

CONCLUSION

Taken together, this is the first detailed study revealing the pattern of TWSV genetic diversity, and population dynamics helping to better understand the ability of this pathogen to drastically reduce the tobacco production in China. Also, this is a valuable addition to the existing worldwide profile of TSWV, especially in China, where a few studies related to TSWV have been reported including only one complete genome of this virus isolated from tobacco plants.

Frankliniella occidentalis pathogenic fungus Lecanicillium interacts with internal microbes and produces sublethal effects

Frankliniella occidentalis (Thysanoptera: Thripidae) is a pest that feeds on various crops worldwide. A prior study identified Lecanicillium attenuatum and L. cauligalbarum as pathogens of F. occidentalis. Unfortunately, the potential of these two entomopathogenic fungi for the biocontrol of F. occidentalis has not been effectively evaluated. The internal microbes (endosymbionts and the gut microbiota) of insects, especially gut bacteria, are crucial in regulating the interactions between the host and intestinal pathogens. The role of thrips internal microbes in the infection of these two entomopathogenic fungi is also unknown. Therefore, biological control of thrips is immediately needed, and to accomplish that, an improved understanding of the internal microbes of thrips against Lecanicillium infection is essential. The virulence of the two pathogenic fungi against F. occidentalis increased with the conidia concentration. Overall, the LC50 of L. cauligalbarum was lower than that of L. attenuatum, and the pathogenicity degree was adult > pupa > nymphs. The activities of protective enzymes include superoxide dismutase (SOD), catalase (CAT), peroxidase (POD); detoxification enzymes include polyphenol oxidase (PPO), glutathione s-transferase (GSTs), and carboxylesterase (CarE); hormones include ecdysone and juvenile hormone; and the composition and proportion of microorganisms (fungi and bacteria) in F. occidentalis infected by L. cauligalbarum and L. attenuatum have changed significantly. According to the network correlation results, there was a considerable correlation among the internal microbes (including bacteria and fungi), enzyme activities, and hormones, which indicates that in addition to bacteria, internal fungi of F. occidentalis are also involved in the L. cauligalbarum and L. attenuatum infection process. In addition, the development time of the surviving F. occidentalis exposed to L. cauligalbarum or L. attenuatum was significantly shorter than that of the control group. Furthermore, the intrinsic rate of increase (rm), finite rate of increase (λ), net reproductive rate (R0), mean generation time (T), and gross reproductive rate (GRR) were significantly lower in the treatment groups than in the control group. L. attenuatum and L. cauligalbarum have biocontrol potential against F. occidentalis. In addition to bacteria, internal fungi of F. occidentalis are also involved in the infection process of insect pathogenic fungi. Disruption of the internal microbial balance results in discernible sublethal effects. Such prevention and control potential should not be ignored. These findings provide an improved understanding of physiological responses in thrips with altered immunity against entomopathogenic fungal infections, which can guide us toward the development of novel biocontrol strategies against thrips.

Identification and characterisation of PRXamide peptides in the western flower thrips, Frankliniella occidentalis

Insect CAPA-PVK (periviscerokinin) and pyrokinin (PK) neuropeptides belong to the PRX family peptides and are produced from capa and pyrokinin genes. We identified and characterised the two genes from the western flower thrips, Frankliniella occidentalis. The capa gene transcribes three splice variants, capa-a, -b, and -c, encoding two CAPA-PVKs (EVQGLFPFPRVamide; QGLIPFPRVamide) and two PKs (ASWMPSSSPRLamide; DSASFTPRLamide). The pyrokinin mRNA encodes three PKs: DLVTQVLQPGQTGMWFGPRLamide, SEGNLVNFTPRLamide, and ESGEQPEDLEGSMGGAATSRQLRTDSEPTWGFSPRLamide, the most extended pheromone biosynthesis activating neuropeptide (PBAN) ortholog in insects. Multiple potential endoproteolytic cleavage sites were presented in the prepropeptides from the pyrokinin gene, creating ambiguity to predict mature peptides. To solve this difficulty, we used three G protein-coupled receptors (GPCRs) for CAPA-PVK, tryptophan PK (trpPK), and PK peptides, and evaluated the binding affinities of the peptides. The binding activities revealed each subfamily of peptides exclusively bind to their corresponding receptors, and were significant for determining the CAPA-PVK and PK peptides. Our biological method using specific GPCRs would be a valuable tool for determining mature peptides, particularly with multiple and ambiguous cleavage sites in those prepropeptides. Both capa and pyrokinin mRNAs were strongly expressed in the head/thorax, but minimally expressed in the abdomen. The two genes also were clearly expressed during most of the life stages. Whole-mounting immunocytochemistry revealed that neurons contained PRXamide peptides throughout the whole-body: four to six neurosecretory cells in the head, and three and seven pairs of immunostained cells in the thorax and abdomen, respectively. Notably, the unusual PRXamide profiles of Thysanoptera are different from the other insect groups.

Star Polymer-Based Nanodelivery System for Pesticides: Enhanced Broad-Spectrum Toxicity and Selective Toxicity

The application of nanotechnology in agriculture can break through many traditional problems of synthetic pesticides, especially for increasing bioactivity and reducing application amount. However, the safety and selective toxicity of nanocarrier-loaded pesticides should be clarified toward natural predators. In this context, an efficient spirotetramat nanodelivery system was successfully constructed based on a star polymer (SPc). Spirotetramat could complex with SPc through hydrogen bonding and van der Waals forces spontaneously. The self-assembly of the spirotetramat/SPc complex decreased the particle size of spirotetramat from 1292 to 710 nm. After the complexation with SPc, the lethal concentration 50 (LC50) values of spirotratemat decreased from 252.064 to 108.871 and 332.079 to 189.257 mg/L toward target pest Frankliniella occidentalis and nontarget predator Orius sauteri with the synergic ratios of 2.315 and 1.755, respectively. The possible reason might be due to the enhancement of the broad-spectrum toxicity of SPc-loaded pesticides. Importantly, the selective toxicity ratio (STR) of spirotetramat increased from 1.32 to 1.73 with the help of SPc, indicating the higher selectivity of the spirotratemat/SPc complex toward predators. Meanwhile, the safety coefficient (SC) of spirotratemat was not significantly changed after complexation with SPc, and the spirotratemat/SPc complex belonged to the medium risk pesticide. Overall, the assembly with SPc could not only improve the control efficacy of spirotetramat but also increase its selectivity as well as alleviate its negative effects on predators. The current study is beneficial for understanding the enhancement of broad-spectrum toxicity and the selective toxicity of nanocarrier-loaded pesticides.

Molecular, biochemical, and toxicological characterization of two acetylcholinesterases from the Western flower thrips, Frankliniella occidentalis

We investigated the molecular and biochemical properties of two acetylcholinesterases (FoAChE1 and FoAChE2) from the Western flower thrips, Frankliniella occidentalis. Polyacrylamide gel electrophoresis and western blotting confirmed the membrane-anchored nature of both FoAChE1 and FoAChE2, which was further supported by hydrophobicity and glycophosphatidylinositol anchor predictions. High expression levels of both enzymes were observed in the head, indicating their predominant distribution in neuronal tissues. FoAChE1 exhibited significantly higher expression levels in all examined tissues compared to FoAChE2, suggesting its major role as a synaptic enzyme. Nonetheless, both recombinant enzymes displayed robust catalytic activity toward acetylthiocholine iodide, and FoAChE1 demonstrated nearly identical catalytic efficiency compared to FoAChE2. FoAChE1 exhibited slightly lower sensitivities to the cholinesterase inhibitors tested, including organophosphates (OPs) and carbamates (CBs), compared to FoAChE2. Field populations of F. occidentalis exhibited polymorphism of alanine vs. serine at position 197 of FoAChE1 within the conserved oxyanion hole. Contrary to common belief, however, functional analysis using recombinant enzymes revealed that neither A197 nor S197 residue was associated with FoAChE1 insensitivity to OPs and CBs. FoAChE2 did not exhibit any polymorphic amino acid substitutions at the positions known to be associated with resistance. Due to the absence of apparent resistance-associated mutations in field populations of F. occidentalis, the judicious use of some OPs or CBs can be suggested for controlling the highly resistant populations to other insecticides. Overall, our findings highlight the significance of both FoAChE1 and FoAChE2 as targets for toxicity assessment, while the specific contribution of each enzyme to toxicity remains unclear.

Evaluation of a guardian plant system to suppress Frankliniella occidentalis (Thysanoptera: Thripidae) in greenhouse ornamentals

BACKGROUND

Western flower thrips (WFT), Franklinella occidentalis (Pergande), is an economically damaging pest of greenhouse ornamentals. A 'guardian plant system' (GPS) that targeted WFT was evaluated under controlled and commercial greenhouse conditions. This system used mycotized millet grains with the entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli) Vuillemin applied to soil of potted marigolds, Tagetes patula (L.), combined with the foliar-dwelling predatory mite Neoseiulus (=Amblyseius) cucumeris (Oudemans) in slow-release sachets under controlled greenhouse conditions, and with the addition of a pheromone lure under commercial settings.

RESULTS

Significantly fewer WFT and less foliar damage on GPS was observed over the 10 and 12 weeks experimental periods compared to the untreated controls. Predatory mites were maintained up to 10 weeks with one release under controlled greenhouse conditions and 12 weeks with two releases in commercial greenhouses. In commercial greenhouses, greater numbers of WFT were found on marigolds than on crop plants within 1 m of the system. Fungal granules persisted for 12 weeks up to 2.5 × 105  CFU g-1 in the GPS soil.

CONCLUSION

The use of biological control agents to suppress WFT within a GPS could be a useful IPM strategy for greenhouse production. The marigold GPS attracted WFT which were suppressed primarily through predation by foliar-dwelling predatory mites and to a lesser extent, infection from conidia produced by the granular fungal formulation in the soil. Further investigations into system deployment and fungal granular application rates and new fungal formulations are suggested to improve system efficacy. © 2023 Society of Chemical Industry.

Chloroplast Genome Engineering: A Plausible Approach to Combat Chili Thrips and Other Agronomic Insect Pests of Crops

The world population's growing demand for food is expected to increase dramatically by 2050. The agronomic productivity for food is severely affected due to biotic and abiotic constraints. At a global level, insect pests alone account for ~20% loss in crop yield every year. Deployment of noxious chemical pesticides to control insect pests always has a threatening effect on human health and environmental sustainability. Consequently, this necessitates for the establishment of innovative, environmentally friendly, cost-effective, and alternative means to mitigate insect pest management strategies. According to a recent study, using chloroplasts engineered with double-strand RNA (dsRNA) is novel successful combinatorial strategy deployed to effectively control the most vexing pest, the western flower thrips (WFT: Frankliniella occidentalis). Such biotechnological avenues allowed us to recapitulate the recent progress of research methods, such as RNAi, CRISPR/Cas, mini chromosomes, and RNA-binding proteins with plastid engineering for a plausible approach to effectively mitigate agronomic insect pests. We further discussed the significance of the maternal inheritance of the chloroplast, which is the major advantage of chloroplast genome engineering.

Selection Behavior and OBP-Transcription Response of Western Flower Thrips, Frankliniella occidentalis, to Six Plant VOCs from Kidney Beans

Plant volatile organic compounds (VOCs) are an important link that mediates chemical communication between plants and plants, plants and insects, and plants and natural enemies of insect pests. In this study, we tested the response in the selective behavior of western flower thrips, Frankliniella occidentalis, to the VOCs of kidney bean, Phaseolus vulgaris L., to explore their "attraction" or "repellent" effects regarding their application in integrated pest management (i.e., IPM). The results indicated that 12.7 μL/mL (E, E, E, E)-squalene, 3.2 μL/mL dioctyl phthalate, and 82.2 μL/mL ethyl benzene had a significantly attractive effect on the selective behavior of F. occidentalis, while 10.7 μL/mL and 21.4 μL/mL 2,6-ditert-butyl-4-methyl phenol had a significantly repulsive effect on the selective behavior of F. occidentalis, showing that F. occidentalis responds differently to specific concentrations of VOCs from P. vulgaris plant emissions. Interestingly, the three compounds with the specific above concentrations, after being mixed in pairs, significantly attracted F. occidentalis compared to the control treatment; however, the mixture with the three above compounds had no significant different effect on F. occidentalis compared to the control treatment. It can be seen that the effect with the mixtures of three kinds of VOCs had the same function and may not get better. Simultaneously, the reasons for this result from the transcription levels of odorant-binding protein genes (OBPs) were determined. There were differences in the types and transcription levels of OBPs, which played a major role in the host selection behavior of F. occidentalis under the mixed treatment of different VOCs. It is presumed that there are specific VOCs from P. vulgaris plants that have a good repellent or attracting effect on the selective behavior of F. occidentalis, which can be used for the development of plant-derived insect attractants and repellents to serve as IPM in fields. But attention should be paid to the antagonism between plant-derived preparations and VOCs produced by plants themselves after application.

Comparison of the biology of Frankliniella intonsa and Megalurothrips usitatus on cowpea pods under natural regimes through an age-stage, two-sex life table approach

Two thrips, Megalurothrips usitatus (Bagnall) and Frankliniella intonsa (Trybom) are major pests of cowpea in South China. To realistically compare the growth, development and reproductive characteristics of these two thrips species, we compared their age-stage, two-sex life tables on cowpea pods under summer and winter natural environmental regimes. The results showed that the total preadult period of M. usitatus was 8.09 days, which was significantly longer than that of F. intonsa (7.06 days), while the adult female longevity of M. usitatus (21.14 days) was significantly shorter than that of F. intonsa (25.77 days). Significant differences were showed in male adult longevity (10.68 days for F. intonsa and 16.95 days for M. usitatus) and the female ratio of offspring (0.67 for F. intonsa and 0.51 for M. usitatus), and the total preadult period of M. usitatus (16.20 days) was significantly longer than that of F. intonsa (13.66 days) in the winter regime. The net reproductive rate (summer: R0 = 85.62, winter: R0 = 105.22), intrinsic rate of increase (summer: r = 0.3020 day-1, winter: r = 0.2115 day-1), finite rate of increase (summer: λ = 1.3526 day-1, winter: λ = 1.2356 day-1) and gross reproduction rate (summer: GRR = 139.34, winter: GRR = 159.88) of F. intonsa were higher than those of M. usitatus (summer: R0 = 82.91, r = 0.2741, λ = 1.3155, GRR = 135.71; winter: R0 = 80.62, r = 0.1672, λ = 1.1820, GRR = 131.26), and the mean generation times (summer: T = 14.73 days, winter: T = 22.01 days) of F. intonsa were significantly shorter than those of M. usitatus (summer: T = 16.11 days, winter: T = 26.25 days). These results may contribute to a better understanding of the bioecology of different thrips species, especially the interspecific competition between two economically important cowpea thrips with the same ecological niche in a changing environment.

Overview of Updated Control Tactics for Western Flower Thrips

Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), broadly known as Western flower thrips (WFT), are currently one of the most critical pests worldwide in field and greenhouse crops, and their management is full of yet unsolved challenges derived from their high reproductive potential, cryptic habit, and ability to disperse. The control of this pest relies widely on chemical control, despite the propensity of the species to develop resistance. However, significant advances have been produced through biological and ethological control. Although there has recently been a remarkable amount of new information regarding the management of this pest worldwide, there is no critical analysis of recent developments and advances in the attractive control tactics for WFT, constituting the present compilation's aim. Hence, this narrative review provides an overview of effective control strategies for managing thrips populations. By understanding the pest's biology, implementing monitoring techniques, accurately identifying the species, and employing appropriate control measures, farmers and researchers can mitigate the WFT impact on agricultural production and promote sustainable pest management practices.

Insecticide Susceptibility and Detoxification Enzyme Activity of Frankliniella occidentalis under Three Habitat Conditions

Frankliniella occidentalis is a highly destructive and invasive agricultural pest that has developed resistance to a variety of insecticide classes. Different planting structures and insecticide use frequency can directly affect the resistance development of F. occidentalis. In this study, the susceptibility of three field strains of F. occidentalis, collected over one year (April to November) from three habitat conditions (facility agriculture area, FA; open field crop area, OF; agroforestry intersection area, AI), to spinetoram, spinosad, emamectin benzoate, chlorfenapyr, acetamiprid, and imidacloprid were monitored and compared. At the same time, the detoxification enzyme activity of F. occidentalis in different habitats was determined. The results showed that the susceptibility of the F. occidentalis population in FA was significantly lower than that of populations from OF and AI. Among them, the F. occidentalis population in FA had developed low levels of resistance to spinetoram (RR = 9.18-fold), emamectin benzoate (RR = 5.47-fold), chlorfenapyr (RR = 6.67-fold), and acetamiprid (RR = 7.49-fold), and had developed moderate level resistance to imidacloprid (RR = 11.67-fold), while still being relatively sensitive to spinosad. The population of F. occidentalis from OF had developed low level resistance to spinetoram (RR = 5.24-fold) but was still relatively sensitive to the other five insecticides. The resistance of F. occidentalis from AI to six insecticides was at relatively sensitive levels. The results of the enzyme activities of detoxification enzymes, including carboxylesterase (CarE), glutathione S-transferase (GST), acetylcholinesterase (AChE), and the cytochrome P450 enzyme system (CYP450), revealed that the activities of the FA population of F. occidentalis were significantly higher than those of the other two populations. The change of CarE activity in F. occidentalis was consistent with that of spinetoram resistance, indicating that CarE may be involved in the metabolic resistance of F. occidentalis to spinetoram. Among the three populations, the resistance and detoxification enzyme activities of F. occidentalis of the FA population to six insecticides were higher than those of the other two populations. Our findings, along with other strategies, are expected to help with the resistance management of F. occidentalis in different habitats.

The Chromosome-Level Genome Assembly of Bean Blossom Thrips (Megalurothrips usitatus) Reveals an Expansion of Protein Digestion-Related Genes in Adaption to High-Protein Host Plants

Megalurothrips usitatus (Bagnall) is a destructive pest of legumes, such as cowpea. The biology, population dynamics and control strategies of this pest have been well studied. However, the lack of a high-quality reference genome for M. usitatus has hindered the understanding of key biological questions, such as the mechanism of adaptation to feed preferentially on high-protein host plants and the resistance to proteinase inhibitors (PIs). In this study, we generated a high-resolution chromosome-level reference genome assembly (247.82 Mb, 16 chromosomes) of M. usitatus by combining Oxford Nanopore Technologies (ONT) and Hi-C sequencing. The genome assembly showed higher proportions of GC and repeat content compared to other Thripinae species. Genome annotation revealed 18,624 protein-coding genes, including 4613 paralogs that were preferentially located in TE-rich regions. GO and KEGG enrichment analyses of the paralogs revealed significant enrichment in digestion-related genes. Genome-wide identification uncovered 506 putative digestion-related enzymes; of those, proteases, especially their subgroup serine proteases (SPs), are significantly enriched in paralogs. We hypothesized that the diversity and expansion of the digestion-related genes, especially SPs, could be driven by mobile elements (TEs), which promote the adaptive evolution of M. usitatus to high-protein host plants with high serine protease inhibitors (SPIs). The current study provides a valuable genomic resource for understanding the genetic variation among different pest species adapting to different plant hosts.

HMG-like DSP1 is a damage signal to mediate the western flower thrips, Frankliniella occidentalis, immune responses to tomato spotted wilt virus infection

Tomato spotted wilt virus (TSWV) causes a serious plant disease and is transmitted by specific thrips including the western flower thrips, Frankliniella occidentalis. The persistent and circulative virus transmission suggests an induction of immune defenses in the thrips. We investigated the immune responses of F. occidentalis to TSWV infection. Immunofluorescence assay demonstrated viral infection in the larval midguts at early stage and subsequent propagation to the salivary gland in adults. In the larval midgut, TSWV infection led to the release of DSP1, a damage-associated molecular pattern, from the gut epithelium into the hemolymph. DSP1 up-regulated PLA₂ activity, which would lead to biosynthesis of eicosanoids that activate cellular and humoral immune responses. Phenoloxidase (PO) activity was enhanced following induction of PO and its activating protease gene expressions. Antimicrobial peptide genes and dual oxidase, which produces reactive oxygen species, were induced by the viral infection. Expression of four caspase genes increased and TUNEL assay confirmed apoptosis in the larval midgut after the virus infection. These immune responses to viral infection were significantly suppressed by the inhibition of DSP1 release. We infer that TSWV infection induces F. occidentalis immune responses, which are activated by the release of DSP1 from the infection foci within midguts.

Attraction of Frankliniella occidentalis Females towards the Aggregation Pheromone Neryl (S)-2-Methylbutanoate and Kairomones in a Y-Olfactometer

An understanding of insect olfaction allows for more specific alternative methods of pest control. We evaluated the responses of the western flower thrips (WFT, Frankliniella occidentalis) in a Y-olfactometer to estimate gas-phase concentrations of the aggregation pheromone neryl (S)-2-methylbutanoate and known kairomones such as methyl isonicotinate, (S)-(-)-verbenone, and p-anisaldehyde. The gas-phase concentrations of these compounds were obtained from the release rates measured in dynamic headspace cells. The compounds were collected from the headspace using dried solid-phase extraction (SPE) cartridges and analyzed with a triple quadrupole GC-MS/MS. We observed that the aggregation pheromone significantly attracted WFT females at doses of 10 and 100 µg, whereas methyl isonicotinate and p-anisaldehyde significantly attracted WFT females at the highest dose. Verbenone did not produce any significant results. A completely different picture was obtained when the gas-phase concentrations were considered. The minimal gas-phase concentrations of the pheromone required to attract WFT females was 0.027 ng/mL, at least 100 times lower than that of the other two compounds. The relevance and implications of our results are discussed in light of the insect's biology and pest management methods.

Why are phytoseiid predatory mites not effectively controlling Echinothrips americanus?

The poinsettia thrips, Echinothrips americanus Morgan (Thysanoptera: Thripidae), is a key pest of various ornamental and vegetable greenhouse crops. As current biological control alternatives lack efficiency, applying chemicals remains the dominant control strategy, thereby heavily disturbing the biocontrol-based integrated management of other pests. For a range of other thrips pests, phytoseiid predatory mites have shown to be effective biocontrol agents, being able to overcome the thrips' physical and chemical defense armory. Here, we investigated potential underlying causes for the lack of phytoseiid efficacy in controlling E. americanus. First, we assessed the nutritional value of E. americanus for the predatory mite Amblydromalus limonicus (Garman and McGregor) (Acari: Phytoseiidae) when its physical or chemical defenses were eliminated by freezing the thrips. The phytoseiid could complete its immature development when frozen thrips instars were offered, but not when these were offered alive. Subsequently, we tested whether adult female A. limonicus had a higher predation rate on first instar E. americanus when they had been given experience with either live or frozen E. americanus during their immature development (i.e., conditioning). Conditioning significantly increased the predation capacity of the phytoseiid. Finally, we tested the control potential of conditioned A. limonicus versus naïve ones when exposed to E. americanus on sweet pepper plants. In contrast to the laboratory trials, at the plant level, conditioning did not yield better control. Possible factors explaining insufficient control of E. americanus by phytoseiids are discussed.

Responses of Thrips hawaiiensis and Thrips flavus populations to elevated CO2 concentrations

Increased atmospheric CO2 concentrations may directly affect insect behavior. Thrips hawaiiensis Morgan and T. flavus Schrank are economically important thrips pests native to China. We studied the development, survival, and oviposition of these two thrips under elevated CO2 concentrations (800 μl liter-1) and ambient CO2 (400 μl liter-1; control) conditions. Both thrips species developed faster but had lower survival rates under elevated CO2 levels compared with control conditions (developmental time: 13.25 days vs. 12.53 days in T. hawaiiensis, 12.18 days vs. 11.61 days in T. flavus; adult survival rate: 70.00% vs. 64.00% in T. hawaiiensis, 65.00% vs. 57.00% in T. flavus under control vs. 800 μl liter-1 CO2 conditions, respectively). The fecundity, net reproductive rate (R0), and intrinsic rate of increase (rm) of the two species were also lower under elevated CO2 concentrations (fecundity: 47.96 vs. 35.44 in T. hawaiiensis, 36.68 vs. 27.88 in T. flavus; R0: 19.83 vs. 13.62 in T. hawaiiensis, 14.02 vs. 9.86 in T. flavus; and rm: 0.131 vs. 0.121 in T. hawaiiensis, 0.113 vs. 0.104 in T. flavus under control and 800 μl liter-1 CO2 conditions, respectively). T. hawaiiensis developed slower but had a higher survival rate, fecundity, R0, and rm compared with T. flavus at each CO2 concentration. In summary, elevated CO2 concentrations negatively affected T. hawaiiensis and T. flavus populations. In a world with higher CO2 concentrations, T. hawaiiensis might be competitively superior to T. flavus where they co-occur.

Detection of Putative Mutation I873S in the Sodium Channel of Megalurothrips usitatus (Bagnall) Which May Be Associated with Pyrethroid Resistance

Pyrethroid resistance of thrips has been reported in many countries, and knockdown resistance (kdr) has been identified as a main mechanism against pyrethroids in many insects. To characterize pyrethroid resistance in Megalurothrips usitatus from the Hainan Province of China, we conducted a biological assay and sequenced the voltage-gated sodium channel gene domain II from M. usitatus field populations. It showed high resistance to the pyrethroids for 2019 and 2020, in which LC₅₀ to lambda-cyhalothrin of M. usitatus was 1683.521 mg/L from Sanya in 2020. The LC₅₀ value of deltamethrin was lower in Haikou than in other locations, which mean the south of Hainan has higher resistance than the north of Hainan. Two mutations of I873S and V1015M were detected in the domain II region of the sodium channel in M. usitatus; however, the mutation frequency of V1015M was only 3.33% and that of I873S was 100%. One is homozygous and the other is a heterozygous mutant type. The three thrips-sensitive strains of sodium channel 873 are highly conserved in amino acids (isoleucine), while the M. usitatus pyrethroid-resistant strains are all serine, so I873S may be related to the resistance of M. usitatus to pyrethroids. The present study will contribute to the understanding of the evolution of pyrethroids resistance and contribute to the development of resistance management of M. usitatus in Hainan.