Semiochemicals for Thrips and Their Use in Pest Management

Exploitation of volatile organic compounds for rice field insect-pest management: current status and future prospects

Insect pests are major biotic factors that cause significant damage to rice crops, posing a major challenge to global rice production. Synthetic pesticides are the most effective and reliable technique for pest management. However, their high cost, non-biodegradability, and adverse effects on human and environmental health have driven the search for more sustainable, eco-friendly, and economically viable alternatives. Recently, Volatile Organic Compounds (VOCs), both plant-derived or synthetically made, have emerged as a promising tool for insect pest management in diverse agricultural practices. Rice plants continuously release VOCs that facilitate tritrophic interactions among the plants, their herbivores, and the natural enemies of these herbivores, highlighting their ecological importance. VOCs are being explored as semiochemicals in pest management strategies in various crops, including rice. Although applications of VOCs remain in the laboratory stage, they hold great promise for future field implementation. This review highlights the role of rice VOCs in herbivore-natural enemy interactions and explores the factors regulating their release. It provides a comprehensive analysis of recent advancements, ongoing challenges, and prospects in using VOCs for rice pest management. Additionally, the review emphasizes the integration of VOCs with precision agriculture and genetic engineering approaches along with advanced monitoring technologies, to develop sustainable and effective pest management practices in rice agroecosystems.

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.

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.

Untargeted Volatile Profiling Identifies Key Compounds Driving the Attraction of Western Flower Thrips to Alstroemeria Cultivars

Western flower thrips (WFTs) are significant pests affecting various crops globally. Developing sustainable strategies for managing WFTs is essential for improving thrips management. Ethological control methods, particularly those employing volatile organic compounds (VOCs) emitted by plants to influence insect behavior, have emerged as a promising avenue for pest management. Natural hosts such as Alstroemeria provide an intriguing yet underexplored opportunity for developing attractants tailored to WFT management. This study examined the behavioral preferences of WFTs towards flowers of four commercial Alstroemeria cultivars, focusing on variations in VOC profiles. Using headspace solid-phase microextraction (HS-SPME), VOCs were captured in vivo from cultivars with contrasting levels of WFT infestation. Gas chromatography coupled with mass spectrometry (GC-MS) was employed to analyze the VOCs, with linear retention indices aiding compound identification. An untargeted volatile profiling-based comparative analysis revealed key VOCs that differed among cultivars, shedding light on their potential correlation with WFT behavior. Behavioral assays identified three specific VOCs-butyl butyrate, 1-methylnaphthalene, and citronellyl acetate-as influential in attracting WFTs. Attraction responses were concentration-dependent, with two tested concentrations eliciting significant behavioral effects. These findings highlight the potential of these active VOCs as components of novel attractants for WFT management. The results direct future research and the development of tools to integrate ethological strategies into sustainable pest management practices for crops.

Chemical compounds associated with Schistocerca piceifrons piceifrons (Orthoptera: Acrididae), by Gas Chromatography-Mass Spectrometry analysis

Semiochemicals are chemicals that mediate inter- and intraspecific interactions between insects. Recently, these chemicals have begun to be investigated as an alternative for the management of the Central American locust, Schistocerca piceifrons piceifrons (Walker, 1870), a pest that can cause substantial damage to crops, pastures, and native vegetation. A suitable method for investigating the range of semiochemicals present in Central American locust is surface washing in organic solvents. In the work described here, the extraction of chemical compounds was carried out with hexane in a 1:10 (w/v) ratio, in 2 resting periods (1 and 24 h) and 2 stages of Central American locust development (young adult and adult in reproductive stage). By Gas Chromatography-Mass Spectrometry, 17 chemical compounds previously identified with semiochemical potential in other insects were detected. The study of semiochemicals in Central American locust offers the opportunity to identify specific chemical compounds that may have the potential to implement management alternatives for this pest. Specific studies of each compound detected in this work are needed to elucidate whether they have semiochemical activity and potential to combat the pest and reduce the environmental damage caused by the application of synthetic chemical products.

Identification and field verification of the aggregation pheromone components produced by male Holotrichia parallela Motschulsky (Coleoptera: Scarabaeidae)

BACKGROUND

The chafer beetle, Holotrichia parallela, causes damage to numerous economically significant crops worldwide. Adult beetles exhibit aggregation behavior likely mediated by a male-produced pheromone. Advancements in biological research technology have facilitated the identification of insect aggregation pheromones and promoted their applications as bait for trapping and monitoring pests. Currently, only a few active components of aggregation pheromones from Holotrichia species have been identified. However, the specific components of aggregation pheromones produced by H. parallela remain unknown.

RESULT

In this study, we initially observed from Y-tube olfactometer assays that both male and female H. parallela were significantly attracted to volatiles emitted by males, but not to those from females. We then collected hindgut crude extracts of male adults and carried out gas chromatography-mass spectrometry analysis to identify potential aggregation pheromone components. Pentadecyl acetate, cis-13-docosenol, and behenic acid were identified as male-specific compounds in comparison to female extracts, serving as components of the aggregation pheromone in H. parallela. We further evaluated their attractiveness to H. parallea in both laboratory and field experiments. In laboratory settings, pentadecyl acetate, cis-13-docosenol, and behenic acid evoked significant responses to both males and females at specific concentrations, as evidenced by both electroantennography tests and behavioral bioassays. Under field conditions, traps baited with these three compounds captured significantly more H. parallela adults compared to control traps.

CONCLUSION

In this study, we found that pentadecyl acetate, cis-13-docosenol, and behenic acid are specifically present in male H. parallela, serving as aggregation pheromones. Both laboratory and field-trapping experiments suggest their potential as monitoring and controlling tools against H. parallela adults. © 2024 Society of Chemical Industry.

Identification of Aggregation Pheromone as an Attractant for Odontothrips loti, A Serious Thrips Pest on Alfalfa

Odontothrips loti (Haliday) (Thysanoptera: Thripidae) is one of the most serious pests on alfalfa, causing direct damage by feeding and indirect damage by transmitting plant viruses. This damage causes significant loss in alfalfa production. Semiochemicals offer opportunities to develop new approaches to thrips management. In this study, behavioral responses of female and male adults of O. loti to headspace volatiles from live female and male conspecifics were tested in a Y-tube olfactometer. The results showed that both male and female adults of O. loti were attracted to the odors released by conspecific males but not those released by females. Headspace volatiles released by female and male adults were collected using headspace solid-phase microextraction (HS-SPME). The active compound in the volatiles was identified by gas chromatography-mass spectrometry (GC-MS). The analysis showed that there was one major compound, (R)-lavandulyl (R)-2-methylbutanoate. The attractive activity of the synthetic aggregation pheromone compound was tested under laboratory and field conditions. In an olfactometer, both male and female adults showed significant preference for synthetic (R)-lavandulyl (R)-2-methylbutanoate at certain doses. Lures with synthetic (R)-lavandulyl (R)-2-methylbutanoate significantly increased the trap catches of sticky white traps at doses of 40-80 µg in the field. This study confirmed the production of aggregation pheromone by O. loti male adults and identified its active compound as (R)-lavandulyl (R)-2-methylbutanoate, providing a basis for population monitoring and mass trapping of this pest.

Mixture of Synthetic Plant Volatiles Attracts More Stick Tea Thrips Dendrothrips minowai Priesner (Thysanoptera: Thripidae) and the Application as an Attractant in Tea Plantations

The stick tea thrip (Dendrothrips minowai) is one of the most serious sucking pests of tea plants (Camellia sinensis) in China, North Korea, and Japan. Plant volatile lures are widely used for both monitoring and mass trapping. Previously, we demonstrated that sticky traps baited with p-anisaldehyde, eugenol, farnesene, or 3-methyl butanal captured significantly more D. minowai in tea plantations, with p-anisaldehyde notably capturing the most. In this study, we showed that D. minowai adults exhibited significantly higher attraction to mixtures of p-anisaldehyde, eugenol, and farnesene compared to an equivalent dose of p-anisaldehyde alone in H-tube olfactometer assays under laboratory conditions. Moreover, in field experiments conducted in 2022, rubber septa impregnated with a ternary blend of p-anisaldehyde, eugenol, and farnesene (at 3-4.5 mg and a ratio of 3:1:1) captured the highest number of adults on sticky traps, outperforming traps bailed with individual components or a solvent control over two weeks. Significantly, the mass trapping strategy employing these lures achieved control efficacies ranging from 62.8% to 70.7% when compared to traps without attractant, which achieved control efficacies of only 14.2% to 35.4% across three test sites in 2023. These results indicate that the combination of p-anisaldehyde, eugenol, and farnesene exhibits an additive or synergistic effect on D. minowai. In conclusion, our findings establish a theoretical framework and provide practical technological support for integrating attractant-based strategies into comprehensive thrips management strategies.

Identification of aggregation pheromones released by the stick tea thrips (Dendrothrips minowai) larvae and their application for controlling thrips in tea plantations

BACKGROUND

The stick tea thrips, Dendrothrips minowai Priesner, is one of the most important sucking pests that seriously infest tea plants (Camellia sinensis) in China. Given that D. minowai exhibit aggregation behaviors in tea plantations, this study evaluated the potential of aggregation pheromones for their control.

RESULTS

H-tube olfactometer assays showed that D. minowai larvae, adult females and adult males were significantly attracted to larvae rather than adult females and males under laboratory conditions. Subsequent gas chromatography-mass spectrometry analysis of volatiles from larvae, identified two larva-specific components: dodecyl acetate and tetradecyl acetate. Electrophysiological and behavioral experiments confirmed the positive response of females and males to dodecyl acetate, tetradecyl acetate, and their blend (1:1.5). Deployment of these aggregation pheromones on sticky traps resulted in a 1.2- to 3.0-fold increase in the capture of D. minowai adults compared with control traps. In addition, deployment of sticky traps baited with these aggregation pheromones within tea plantations resulted in a noteworthy reduction in the population of adult thrips per 100 leaves, 10 days following trap deployment. The reduction ranged from 29% to 59%, in comparison with the control.

CONCLUSION

D. minowai larvae produce aggregation pheromones, dodecyl acetate and tetradecyl acetate, that can be useful for controlling tea thrips. © 2023 Society of Chemical Industry.

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.

Semiochemicals Associated with the Western Flower Thrips Attraction: A Systematic Literature Review and Meta-Analysis

The study of the semiochemicals of the western flower thrips (WFT), Frankliniella occidentalis, Pergande (Thysanoptera: Thripidae), is a relevant topic that spans the last two decades. Approximately a hundred articles published on this subject from 2000 to 2022 can be found in academic databases, representing approximately 5% of the research on this important pest. These topics have generated a platform for novel research with a high potential for development. However, to move on to a new research step, an effectiveness evaluation of the compounds discovered so far is necessary. This review conducted a systematic analysis of the research focused on the semiochemicals (kairomones, pheromones, and attractants) for this pest. Papers from the past three decades on WFT attraction to semiochemicals were collected from databases using the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The number of individuals attracted to compounds was extracted from the papers and compiled for analysis. With this information, an attraction ratio was calculated. Forty-one possible attractants were found in the literature, with methyl isonicotinate being the most-studied compound so far, with the third-highest attraction ratio. δ-Decalactone was the compound with the highest attraction ratio, but it was one of the least studied. A meta-analysis of the WFT choosing proportion was performed for the compounds with more trials found in the literature. The predicted mean choice percentages for methyl isonicotinate (MIN) and Lurem-TR, the MIN's commercial product, were 76.6% and 66.6%, respectively. There was a convergence among the analyzed studies showing a high degree of research focus on the same group of nitrogen-containing compounds (mainly the pyridine structure). These findings call for future research to diversify the discovery and evaluation of attractive compounds in this relevant study area.

A push-pull strategy to control the western flower thrips, Frankliniella occidentalis, using alarm and aggregation pheromones

Since the first report in 1993 in Korea, the western flower thrips, Frankliniella occidentalis, has been found in various crops throughout the country. Although more than 20 different chemical insecticides are registered to control this insect pest, its outbreaks seriously damage crop yields, especially in greenhouses. This study developed a non-chemical technique to control F. occidentalis infesting hot peppers cultivated in greenhouses. The method was based on behavioral control using an alarm pheromone ("Push") to prevent the entry of the thrips into greenhouses and an aggregation pheromone ("Pull") for mass trapping inside the greenhouses. The greenhouse fences were treated with a wax formulation of the alarm pheromone and a yellow CAN trap covered with sticky material containing the aggregation pheromone was constructed and deployed inside the greenhouses. Field assay demonstrated the efficacy of the push-pull tactics by reducing thrips density in flowers of the hot peppers as well as in the monitoring traps. Especially, the enhanced mass trapping to the CAN trap compared to the conventional yellow sticky trap led to significant reduction in the thrips population. This novel push-pull technique would be applicable to effectively control F. occidentalis in field conditions.

e Silva J, Santos de Oliveira C, Moritz G. Investigation of the spermathecal morphology, reproductive strategy and fate of stored spermatozoa in three important thysanopteran species

In insects, females can keep sperm capable of fertilisation over a long period with the help of the spermatheca. The effectiveness of storing fertile sperm is expected to reflect in the reproductive strategy and, thus, the morphology of the involved organs. In this work, we focused on the relationship between reproduction and morphology in the haplodiploid Thysanoptera, especially if a loss of these traits occurs under thelytoky. The spermathecal morphology and the fate of stored spermatozoa were studied by microscopic techniques (high-resolution x-ray computed tomography and transmission electron microscopy) in three species with different reproductive modes and lifestyles (Suocerathrips linguis, Echinothrips americanus, Hercinothrips femoralis). Mating experiments were conducted to analyse the use of the transferred sperm in the thelytokous H. femoralis. Results show that the spermathecae are relatively simple, which can be explained by the availability of sperm and the short lifespan of the females. However, the spermatheca in H. femoralis seems to be vestigial compared to the arrhenotokous species and females do not use sperm for fertilisation. No substantial change was observed in the structure of spermatozoa, despite an enlargement of the sperm organelles being measured during storage in all three species. The results of this work demonstrate differences in the morphology of the spermatheca, especially concerning the reproduction mode, promoting the understanding of the complex interaction between morphology and behaviour.

Colour vision in thrips (Thysanoptera)

Insects are an astonishingly successful and diverse group, occupying the gamut of habitats and lifestyle niches. They represent the vast majority of described species and total terrestrial animal biomass on the planet. Their success is in part owed to their sophisticated visual systems, including colour vision, which drive a variety of complex behaviours. However, the majority of research on insect vision has focused on only a few model organisms including flies, honeybees and butterflies. Especially understudied are phytophagous insects, such as diminutive thrips (Thysanoptera), in spite of their damage to agriculture. Thrips display robust yet variable colour-specific responses despite their miniaturized eyes, but little is known about the physiological and ecological basis of their visual systems. Here, we review the known visual behavioural information about thrips and the few physiological studies regarding their eyes. Eye structure, spectral sensitivity, opsin genes and the presence of putative colour filters in certain ommatidia strongly imply dynamic visual capabilities. Finally, we discuss the major gaps in knowledge that remain for a better understanding of the visual system of thrips and why bridging these gaps is important for expanding new possibilities for applied pest management strategies for these tiny insects. This article is part of the theme issue 'Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods'.

A Preparation Method of Nano-Pesticide Improves the Selective Toxicity toward Natural Enemies

Various nano-delivery systems have been designed to deliver synthetic/botanical pesticides for improved bioactivity. However, the enhanced toxicity of nanocarrier-loaded pesticides may injure the natural enemies, and their selective toxicity should be evaluated before the large-scale application. In this context, a star polymer (SPc)-based cyantraniliprole (CNAP) nano-delivery system was constructed, and its selective toxicity was evaluated using pest Frankliniella occidentalis (WFT) and predator Orius sauteri. The amide NH of CNAP could assemble with carbonyl groups or tertiary amines of SPc through hydrogen bonds to form CNAP/SPc complex spontaneously. The above self-assembly decreased the particle size of CNAP from 808 to 299 nm. With the help of SPc, the lethal concentration 50 (LC₅₀) values of CNAP decreased from 99 to 54 mg/L and 230 to 173 mg/L toward WFTs and O. sauteri due to the enhancement of broad-spectrum bioactivity. Interestingly, the toxicity selective ratio (TSR) of CNAP increased from 2.33 to 3.23 with the help of SPc, revealing the higher selectivity of SPc-loaded CNAP. To our knowledge, it was the first successful exploration of the selective toxicity of nanocarrier-loaded pesticides, and the higher selective toxicity of SPc-loaded CNAP was beneficial for alleviating the negative impacts on predators.

Contrasting National Plant Protection Needs, Perceptions and Techno-Scientific Capabilities in the Asia-Pacific Region

Pests and pathogens inflict considerable losses in global agri-food production and regularly trigger the (indiscriminate) use of synthetic pesticides. In the Asia-Pacific, endemic and invasive organisms compromise crop yields, degrade farm profitability and cause undesirable social-environmental impacts. In this study, we systematically assess the thematic foci, coherence and inclusiveness of plant protection programs of 11 Asia-Pacific countries. Among 23 economically important diseases and 55 pests, survey respondents identified rice blast, rice brown planthopper, citrus greening disease, Tephritid fruit flies and fall armyworm as threats of regional allure. These organisms are thought to lower crop yields by 20–35% and cause management expenditures up to US$2,250 per hectare and year. Though decision-makers are familiar with integrated pest management (IPM), national programs are invariably skewed toward curative pesticide-intensive control. Pesticide reductions up to 50–100% are felt to be feasible and potentially can be attained through full-fledged IPM campaigns and amended policies. To rationalize farmers' pesticide use, decision criteria (e.g., economic thresholds) wait to be defined for multiple crop x pest systems and (participatory) training needs to be conducted e.g., on (pest, disease) symptom recognition or field-level scouting. Efforts are equally needed to amend stakeholder perceptions on ecologically based measures e.g., biological control. Given that several Asia–Pacific countries possess robust techno-scientific capacities in various IPM domains (e.g., taxonomy, molecular diagnostics, socioeconomics), they can take on an active role in regionally coordinated campaigns. As such, one can reinvigorate IPM and ensure that preventative, non-chemical pest management ultimately becomes the norm instead of the exception throughout the Asia–Pacific.

Colour Response in Western Flower Thrips Varies Intraspecifically

Discrepancies in the published research as to the attraction of the economically important pest western flower thrips (WFT) to different colours confounds the optimisation of field traps for pest management purposes. We considered whether the different experimental conditions of independent studies could have contributed to this. Therefore, the behavioural response (i.e., landings) to different colour cues of two WFT laboratory populations from Germany (DE) and The Netherlands (NL), which had previously been independently shown to have different colour preferences, were tested in the same place, and under the same experimental conditions. Single-choice wind tunnel bioassays supported previous independent findings, with more of a NL population landing on the yellow LED lamp (588 nm) than the blue (470 nm) (p = 0.022), and a not-statistically significant trend observed in a DE population landing more on blue compared to yellow (p = 0.104). To account for potential original host rearing influences, both populations were subsequently established on bean for ~20 weeks, then yellow chrysanthemum for 4−8 and 12−14 weeks and tested in wind tunnel choice bioassays. Laboratory of origin, irrespective of the host plant rearing regime, remained a significant effect (p < 0.001), with 65% of the NL WFT landing on yellow compared to blue (35%), while 66% of the DE WFT landed on blue compared to yellow (34%). There was also a significant host plant effect (p < 0.001), with increased response to yellow independent of laboratory of origin after rearing on chrysanthemum for 12−14 weeks. Results suggest that differing responses of WFT populations to colour is, in this case, independent of the experimental situation. Long-term separate isolation from the wild cannot be excluded as a cause, and the implications of this for optimising the trap colour is discussed.

Spinetoram resistance drives interspecific competition between Megalurothrips usitatus and Frankliniella intonsa

BACKGROUND

Species displacement by the outcome of interspecific competition is of particular importance to pest management. Over the past decade, spinetoram has been extensively applied in control of the two closely related thrips Megalurothrips usitatus and Frankliniella intonsa worldwide, while whether its resistance is implicated in mediating interspecific interplay of the two thrips remains elusive to date.

RESULTS

Field population dynamics (from 2017 to 2019) demonstrated a trend toward displacement of F. intonsa by M. usitatus on cowpea crops, supporting an existing interspecific competition. Following exposure to spinetoram, M. usitatus became the predominate species, which suggests the use of spinetoram appears to be responsible for mediating interspecific interactions of the two thrips. Further annual and seasonal analysis (from 2016 to 2020) of field-evolved resistance dynamics revealed that M. usitatus developed remarkably higher resistance to spinetoram compared to that of F. intonsa, implying a close relationship between evolution of spinetoram resistance and their competitive interactions. After 12 generations of laboratory selection, resistance to spinetoram in M. usitatus and F. intonsa increased up to 64.50-fold and 28.33-fold, and the average realized heritability (h² ) of resistance was calculated as 0.2550 and 0.1602, respectively. Interestingly, two-sex life table analysis showed that the spinetoram-resistant strain of F. intonsa exhibited existing fitness costs, but not the M. usitatus. These indicate that a rapid development of spinetoram resistance and the lack of associated fitness costs may be the mechanism underlying recent dominance of M. usitatus over F. intonsa.

CONCLUSION

Collectively, our results uncover the involvement of insecticide resistance in conferring displacement mechanism behind interspecific competition, providing a framework for understanding the significance of the evolutionary relationships among insects under ongoing changing environments. These findings also can be invaluable in proposing the most appropriate strategies for sustainable thrips control programs. © 2022 Society of Chemical Industry.

Evaluation of Selected Plant Volatiles as Attractants for the Stick Tea Thrip Dendrothrips minowai in the Laboratory and Tea Plantation

Simple Summary

The stick tea thrip Dendrothrips minowai is a key pest in tea plantations in China. In recent years, plant-derived semiochemicals have attracted considerable attention as promising attractants for the management of thrips, due to their safety and low cost. In this study, compounds that have been reported to attract other thrips or emitted from tea plants were evaluated for their electroantennogram (EAG), behavioral tests and field trapping efficacy for D. minowai. The EAG relative response value of D. minowai evoked by p-anisaldehyde, 3-methyl butanal, (E)-β-ocimene, farnesene, nonanal, eugenol, (+)-α-pinene, limonene, (−)-α-pinene, and γ-terpinene was significantly higher than the other compounds. Meanwhile, p-anisaldehyde, eugenol, farnesene, methyl benzoate, 3-methyl butanal, (E)-β-ocimene, (−)-α-pinene, (+)-α-pinene, and γ-terpinene led to attraction or repellency responses of female D. minowai. In addition, trap capture numbers of female D. minowai on sticky traps baited with p-anisaldehyde, eugenol, farnesene, and 3-methyl butanal were significantly higher than the control in tea plantations. Overall, our results highlight the potential application of plant volatiles in the development of effective, eco-friendly lure formulations for use in the monitoring and management of thrips.

Abstract

The stick tea thrip (Dendrothrips minowai Priesner) is the main pest thrip in tea (Camellia sinensis) plantations in China, and seriously affects the quality and yield of tea. Plant-derived semiochemicals provide an alternative to pheromones as lures and these compounds possess powerful attractiveness. In this study, we selected 20 non-pheromone semiochemicals, including compounds that have been reported to attract other thrips and some volatiles emitted from tea plants as the potential attractant components for D. minowai. In electroantennogram (EAG) assays, 10 synthetic compounds (p-anisaldehyde, 3-methyl butanal, (E)-β-ocimene, farnesene, nonanal, eugenol, (+)-α-pinene, limonene, (−)-α-pinene, and γ-terpinene) elicited significant antennal responses in female D. minowai. In addition, a two-choice H-tube olfactometer bioassay showed that D. minowai displayed significant positive responses to eight compound dilutions (p-anisaldehyde, eugenol, farnesene, methyl benzoate, 3-methyl butanal, (E)-β-ocimene, (−)-α-pinene, and (+)-α-pinene) when compared with the solvent control at both 1 and 2 h. Moreover, γ-terpinene exhibited a significantly deterrent effect on D. minowai. Finally, trap catches of four compounds (p-anisaldehyde, eugenol, farnesene, and 3-methyl butanal, respectively) significantly increase in tea plantations. Among these, the maximum number of D. minowai collected by blue sticky traps baited with p-anisaldehyde was 7.7 times higher than the control. In conclusion, p-anisaldehyde, eugenol, farnesene, and 3-methyl butanal could significantly attract D. minowai in the laboratory and under field conditions, suggesting considerable potential as commercial attractants to control D. minowai populations.

Reproductive Isolation in the Cryptic Species Complex of a Key Pest: Analysis of Mating and Rejection Behaviour of Onion Thrips (Thrips tabaci Lindeman)

Simple Summary

The onion thrips (Thrips tabaci), which is a key pest worldwide, includes three characteristic, distinct groups (i.e., lineages) under the same species name. In the current report, we addressed the question of whether individuals from these lineages recognize and assess each other as potential mating partners. We demonstrated that at least two of these lineages do not belong to the same species, since under our laboratory conditions no mating occurred between them. Moreover, specimens from these cross pairings often exhibited an escape response upon contact with the other thrips, while most of the pairs from the same lineages readily mated at their first interaction. The behaviour of males clearly indicated that they can assess the mating status of a female and usually only try to copulate with virgins. Our findings are important not only because in agriculture it is vital to know whether morphologically similar entities belong to the same species, but also because knowledge about the communication of insects and the possible role of the cues involved can help the development of new plant protection techniques.

Abstract

Thrips tabaci Lindeman is a serious pest of various cultivated plants, with three, distinct lineages within a cryptic species complex. Despite the well-known significance of this pest, many attributes of these lineages are not yet fully understood, including their reproductive behaviour. We performed no-choice-design cross-mating experiments under a controlled laboratory environment with virgin adult individuals from all three lineages. The behaviour of thrips was recorded with a camera mounted on a stereomicroscope, and the recordings were analysed in detail. We found that the so-called leek-associated lineages of this cryptic species complex are reproductively isolated from the tobacco-associated lineage; therefore, they represent different species. Divergence in the behaviour of conspecific and heterospecific pairs became evident only after contact. There were no marked differences between the lineages in their precopulatory and copulatory behaviour, except in the duration of the latter. We confirmed mating between thelytokous females and arrhenotokous males; however, we assume some form of loss of function in the sexual traits of asexual females. The post-mating behaviour of males indicated the presence and role of an anti-aphrodisiac pheromone. We also demonstrated differences between lineages regarding their activity and their propensity for exhibiting an escape response upon interaction with heterospecific thrips.

Mating behaviour, mate choice and female resistance in the bean flower thrips (Megalurothrips sjostedti)

Many species of thrips (Thysanoptera) in the family Thripidae form mating aggregations, but the adaptive significance of these aggregations and the extent of male and female mate choice is poorly understood. We studied the mating behaviour of the bean flower thrips Megalurothrips sjostedti (Trybom) (Thysanoptera: Thripidae), which forms male aggregations and occurs across sub-Saharan Africa. We tested whether males choose mates by female age or mating status. No-choice mating bioassays with one male and one female were used to simulate the way males usually encounter only one female at a time in aggregations in the field. Virgin females violently resisted mating attempts by males, but we found no compelling evidence to establish whether this was indiscriminate or was screening suitable males. Younger males (1–2 days old) did not discriminate females by age (1–2 or 7–10 days old), but older males (7–10 days old) avoided mating with older females. Any male choice by female mating status (virgin or mated) was weak or absent. The mating behaviour of M. sjostedti shows broad similarities with that of other thrips species that form aggregations, but also shows some distinct and novel differences, which can help our understanding of the adaptive significance of aggregations.