Diaphorina citri Induces Huanglongbing-Infected Citrus Plant Volatiles to Repel and Reduce the Performance of Propylaea japonica

Binding properties of olfactory proteins to host volatiles, free fatty acids and cuticular hydrocarbons in the termite Reticulitermes aculabialis

As eusocial insects prevalent in tropical and subtropical regions, termites are characterized by highly organized behaviors and exceptional adaptability, rooted in caste differentiation and chemical communication. These traits make them excellent models for studying insect social structures and ecological interactions. Investigating how termites use chemical signals to perceive and respond to their environment provides insights into their coordination and adaptation within complex ecosystems. This study delved into the chemosensory mechanisms of Reticulitermes aculabialis, examining the interactions of four olfactory proteins with 70 ligands, including host volatiles, cuticular hydrocarbons (CHCs), and free fatty acids (FFAs). Molecular docking simulations revealed varied affinities of the olfactory proteins for long-chain hydrocarbons (n-C23 to n-C28), suggesting a nuanced chemical communication system through specific hydrocarbon detection. RacuCSP1 and RacuCSP2 exhibited specific binding to linoleic acid and undecanoic acid, respectively, highlighting the significance of FFAs in the physiological and behavioral processes of termites. The four olfactory proteins showed a strong affinity for longifolene in fluorescence competitive binding experiments. Notably, RacuOBPs exhibited unique affinities for terpenoid volatiles such as β-lonone and neocembrene, while RacuCSPs specifically bound with terpenoids like 3-carene, myrtenol, α-pinene oxide and β-pinene indicating their critical roles in host detection. Behavioral observations following gene silencing revealed that RacuOBP5 was essential for recognizing longifolene and α-lonone recognition, while RacuCSP1 was key for detecting α-pinene in termites. These findings enhance our understanding of the termite chemosensory system and offer insights for developing precise pest management strategies.

Penicillium-Infected Apples Benefit Larval Development of Conogethes punctiferalis via Alterations of Their Gut Bacteria Community and Gene Expression

Pathogenic microorganisms can impact the behavior and physiology of herbivores by direct or indirect means. This study demonstrated that yellow peach moth Conogethes punctiferalis larvae feeding on Penicillium-infected apples exhibited significantly longer body length and weight parameters compared to the control group. The sequencing of gut 16S rRNA showed a significant increase in the diversity and abundance of bacteria in the larvae feeding on Penicillium-infected apples. Additionally, transcriptomic sequencing of the larval gut indicated significant upregulation of genes related to digestion and cuticle formation after consuming Penicillium-infected apples. Furthermore, enzyme activity assays revealed notable changes in the trypsin and lipase activity. Consequently, these alterations in gut microbiota structure, diversity, and gene expression levels may underlie the observed growth and developmental variations in C. punctiferalis larvae mediated by pathogenic microorganisms. This study holds theoretical significance for a deeper understanding of the tripartite interaction among microorganisms, insects, and plants as well as for the development of novel pest control measures based on gut microbiota.

Specific volatiles of tea plants determine the host preference behavior of Empoasca onukii

Empoasca onukii is a major pest that attacks tea plants. To seek effective and sustainable methods to control the pest, it is necessary to assess its host preference among different species of tea and understand the critical factors behind this behavior. In this study, the behavioral preference of E. onukii for volatile organic compounds (VOCs) of three potted tea species was evaluated. The VOCs released by the three tea species were analyzed using gas chromatography-mass spectrometry, and the major components were used to test the pest's preference. Transcriptome analysis was used to infer the key genes that affect the biosyntheses of the VOCs. The results showed that the tendency of E. onukii toward the VOCs of the three tea species was the strongest in green tea, followed by white tea, and the weakest in red tea. This behavioral preference was significantly and positively correlated with the relative levels of hexanol, linalool, and geraniol in tea volatiles. Relative hexanol was significantly and positively correlated with the expression of genes TEA009423 (LOX2.1), TEA009596 (LOX1.5), TEA008699 (HPL), TEA018669 (CYPADH), and TEA015686 (ADHIII). Relative linalool was significantly and positively correlated with the expression of genes TEA001435 (CAD) and Camellia_sinensis_newGene_22126 (TPS). Relative geraniol was significantly and positively correlated with the expression of genes TEA001435 (CAD), TEA002658 (CYP76B6), TEA025455 (CYP76T24), and Camellia_sinensis_newGene_22126 (TPS). The above findings suggested that three volatiles (hexanol, linalool, and geraniol) determined the behavioral preference of E. onukii toward tea plants, and their biosynthesis was mainly affected by nine genes (TEA009423, TEA009596, TEA008699, TEA018669, TEA015686, TEA001435, TEA002658, TEA025455, and Camellia_sinensis_newGene_22126).

Effects of Crop Resistance on the Tritrophic Interactions between Wheat Lines, Schizaphis graminum (Hemitera: Aphididae), and Propylaea japonica (Coleoptera: Coccinellidae)

Crop resistance and biological control are both considered efficient and environmentally friendly methods of sustainable pest control. In this study, we aimed at investigating the direct influence of four wheat lines with varying resistance level on the life-history traits of the greenbug, Schizaphis graminum, and the mediational effect on the functional response of a predatory ladybird, Propylaea japonica, under laboratory conditions. Results showed that the aphid fitness was the lowest for aphids that had been feeding on wheat line '98-10-19' for one year. These aphids had the longest development time, and least adult mass, minimal mean relative growth rate, and lowest reproductive fitness. In contrast, the aphids that fed on wheat line '98-10-30' were the fittest, with the shortest development time and highest levels of reproductive fitness. The predatory activities of the ladybeetle, especially the adult male significantly decreased following the consumption of aphids belonging to the '98-10-19'-acclimated population. However, there were no significant differences in predatory efficiency (net attack frequency) among the four aphid acclimated populations. Our results showed that the wheat line '98-10-19' has a relative higher resistance to S. graminum than the other three wheat lines, which could further decrease the amount of prey available for consumption. However, the ecological effect of the resistance of '98-10-19' to S. graminum posed no negative influence on the biocontrol potential of P. japonica to these aphids, as their predatory efficiency increases at the fourth instar larvae phase.

Phytopathogens Increase the Preference of Insect Vectors to Volatiles Emitted by Healthy Host Plants

Phytopathogen infections not only affect the physiology of host plants but also the preference of insect vectors; these modifications may increase the spread of infection. For this, we determined the effects of "Candidatus Liberibacter asiaticus" (CLas) infection on the preference of an insect vector (Diaphorina citri) for its uninfected or CLas-infected host (Citrus sinensis) and found that the infected vector preferred uninfected citrus, while the uninfected vector preferred infected citrus. We identified two compounds, (Z)-3 hexenyl and methyl salicylate, that were differentially abundant in the volatiles emitted by infected and uninfected citrus and two odorant-binding protein (OBP) genes differentially expressed between infected and uninfected vectors. The results of receptor-ligand binding assays indicated that CLas upregulated OBP A10 expression in the infected vector to target (Z)-3 hexenyl acetate emitted by uninfected citrus and induced citrus to emit more methyl salicylate for binding to OBP2 in the uninfected vector. Our results might be useful for the effective control of CLas infections.

Urbanization and plant pathogen infection interact to affect the outcome of ecological interactions in an experimental multitrophic system

Urbanization can change interactions in insect communities, and the few studies of tritrophic interactions in urban settings focus on interactions between plants, herbivorous insects and their mutualists and natural enemies. Plant pathogen infection is also widespread and common, and infection may also alter such interactions, but we have no understanding of whether the ecological consequences of pathogen infection vary with urbanization. Using replicated aphid colonies on experimental plants, we investigated how infection by the plant pathogen Botrytis cinerea influences interactions between plants, aphids and the aphid natural enemies and ant mutualists in highly urbanized, suburban and rural study sites. Aphid and natural enemy abundance were highest in the suburban site, while mutualist ants were most abundant in the urban site, reversing the usual positive density-dependent relationship between natural enemies and aphids. The effect of pathogen infection varied with trait and site, mediated by natural enemy preference for hosts or prey on uninfected plants. The effect of infection on aphid abundance was only seen in the suburban site, where natural enemies were most abundant on uninfected plants and aphid numbers were greatest on infected plants. In the urban site, there was no effect of infection, while in the rural site, aphid numbers were lower on infected plants. Uninfected plants were smaller than infected plants and differed between locations. This study suggests that the effects of urbanization on ecological interactions may become more complex and difficult to predict as we study ecological assemblages and communities at greater levels of structural complexity.

Behavioral Responses of Asian Citrus Psyllid (Hemiptera: Liviidae) to Salinity-Stressed Citrus

Most commercial citrus varieties are intolerant of salinity stress, but some rootstocks, such as Rangpur lime, tolerate moderately saline irrigation water. Development of salinity-tolerant citrus may allow for citriculture in semiarid and arid regions where salinity stress is problematic. Because salinity stress influences shoot growth in citrus, we compared the behavioral responses of Asian citrus psyllid, Diaphorina citri Kuwayama, to salinity-stressed versus nonstressed Rangpur lime seedlings. The effects of salinity stress on key physiological processes in the seedlings were also examined. Seedlings in the control group were fertilized with a solution having a salinity of 1.7 dS m-1 while seedlings in the salinity-stressed group were fertilized with a solution having a salinity of 10 dS m-1. The seedlings were exposed to salinity stress for increasing durations (15, 20, or 60 d). Seedlings presented differential physiological responses 15 d after the imposition of salinity stress, and differences in psyllid settling rate on control versus salinity-stressed seedlings were discernable within 1 h following the imposition of salinity stress. The levels of settling, oviposition, and egg survivorship were significantly lower on salinity-stressed versus control seedlings. Olfactometer tests showed that female psyllids preferred the odor from control seedlings, suggesting that the odors of control and salinity-stressed seedlings were different. The results showed that D. citri avoids salinity-stressed seedlings; this suggests the possibility of using moderate salinity stress as a management strategy to minimize psyllid settlement and reproduction and to reduce the spread of huanglongbing, especially in citrus grown in semiarid and arid areas.

Methyl Salicylate Fails to Enhance Arthropod Predator Abundance or Predator to Pest Ratios in Cotton

Conservation biological control is a fundamental tactic in integrated pest management (IPM). Greater biological control services can be achieved by enhancing agroecosystems to be more favorable to the presence, survival, and growth of natural enemy populations. One approach that has been tested in numerous agricultural systems is the deployment of synthetic chemicals that mimic those produced by the plant when under attack by pests. These signals may attract arthropod natural enemies to crop habitats and thus potentially improve biological control activity locally. A 2-yr field study was conducted in the cotton agroecosystem to evaluate the potential of synthetic methyl salicylate (MeSA) to attract native arthropod natural enemies and to enhance biological control services on two key pests. Slow-release packets of MeSA were deployed in replicated cotton plots season long. The abundance of multiple taxa of natural enemies and two major pests were monitored weekly by several sampling methods. The deployment of MeSA failed to increase natural enemy abundance and pest densities did not decline. Predator to prey ratios, used as a proxy to estimate biological control function, also largely failed to increase with MeSA deployment. One exception was a season-long increase in the ratio of Orius tristicolor (White) (Hemiptera: Anthocoridae) to Bemisia argentifolii Bellows and Perring (= Bemisia tabaci MEAM1) (Hemiptera: Aleyrodidae) adults within the context of biological control informed action thresholds. Overall results suggest that MeSA would not likely enhance conservation biological control by the natural enemy community typical of U.S. western cotton production systems.

Diamondback Moth Larvae Trigger Host Plant Volatiles that Lure Its Adult Females for Oviposition

The diamondback moth (DBM) is a destructive pest of crucifer crops. In this study, DBM larvae shown to herbivore induced plant volatiles (HIPVs) that were attractive to adult females exposed in a Y-tube olfactometer. Our results showed that olfactory responses of adult females to HIPVs induced by third instar larvae feeding on Barbarea vulgaris were significantly higher (20.40 ± 1.78; mean moths (%) ± SD) than those induced by first instar larvae (14.80 ± 1.86; mean moths (%) ± SD). Meanwhile, a significant concentration of Sulphur-containing isothiocyanate, 3-methylsulfinylpropyl isothiocyanate, and 4-methylsulfinyl-3-butenyl isothiocyanate were detected in HIPVs released by third instar larvae compared to those released by first instar larvae while feeding on B. vulgaris. When the DBM females were exposed to synthetic chemicals, singly and in blend form, a similar response was observed as to natural HIPVs. Our study demonstrated that the relationship between isothiocyanates acting as plant defense compounds, host plant cues emission and regulation of the DBM adult female behavior due to key volatile triggered by the DBM larvae feeding on B. vulgaris.

Host Plant Species of Bemisia tabaci Affect Orientational Behavior of the Ladybeetle Serangium japonicum and Their Implication for the Biological Control Strategy of Whiteflies

Serangium japonicum Chapin (Coleoptera: Coccinellidae) is a predominant predator with a preference for Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). To date, the orientational behavior of S. japonicum toward B. tabaci-infested plants has seldom been reported. In this study, greenhouse cage experiments and bioassays with wind tunnels, a Y-tube olfactometer and B. tabaci-induced plant volatiles were executed to clarify this behavior. In greenhouse cage experiments, B. tabaci adults significantly preferred eggplant, cucumber and tobacco to cotton and tomato, whereas S. japonicum adults preferred B. tabaci-infested eggplant, cucumber and cotton to tobacco and tomato. In wind tunnel bioassays, B. tabaci showed a clear preference for eggplant, cucumber and tobacco. Compared with B. tabaci-infested eggplant, cucumber or cotton, B. tabaci-infested tobacco was rarely visited by S. japonicum. In Y-tube bioassays, S. japonicum did not distinguish between B. tabaci-infested and uninfested eggplant. Nine common plant volatiles were detected in different plant species, suggesting that these volatiles may play an important role in the process by which S. japonicum looks for prey. In light of the current results, we discuss the implications of our findings and put forward to a new strategy—i.e., an eggplant + B. tabaci + S. japonicum system—to control B. tabaci damage in the integrated management of whitefly.

Host plants alter their volatiles to help a solitary egg parasitoid distinguish habitats with parasitized hosts from those without

When attacked by herbivores, plants emit volatiles to attract parasitoids and predators of herbivores. However, our understanding of the effect of plant volatiles on the subsequent behaviour of conspecific parasitoids when herbivores on plants are parasitized is limited. In this study, rice plants were infested with gravid females of the brown planthopper (BPH) Nilaparvata lugens for 24 hr followed by another 24 hr in which the BPH eggs on plants were permitted to be parasitized by their egg parasitoid, Anagrus nilaparvatae; volatiles from rice plants that underwent such treatment were less attractive to subsequent conspecific parasitoids compared to the volatiles from plants infested with gravid BPH females alone. Chemical analysis revealed that levels of JA and JA-Ile as well as of four volatile compounds-linalool, MeSA, α-zingiberene and an unknown compound-from plants infested with BPH and parasitized by wasps were significantly higher than levels of these compounds from BPH-infested plants. Laboratory and field bioassays revealed that one of the four increased chemicals-α-zingiberene-reduced the plant's attractiveness to the parasitoid. These results suggest that host plants can fine-tune their volatiles to help egg parasitoids distinguish host habitats with parasitized hosts from those without.

Thrips as the Transmission Bottleneck for Mixed Infection of Two Orthotospoviruses

Mixed infections provide opportunities for viruses to increase genetic diversity by facilitating genomic reassortment or recombination, and they may lead to the emergence of new virus species. Mixed infections of two economically important orthotospoviruses, Tomato spotted wilt orthotospovirus (TSWV) and Impatiens necrotic spot orthotospovirus (INSV), were found in recent years, but no natural reassortants between INSV and TSWV were ever reported. The goal of this study was to establish how vector preferences and the ability to transmit INSV and TSWV influence transmission and establishment of mixed infections. Our results demonstrate that thrips prefer to oviposit on TSWV and INSV mixed-infected plants over singly infected or healthy plants, providing young nymphs with the opportunity to acquire both viruses. Conversely, we observed that thrips served as a bottleneck during transmission and favored transmission of one of the two viruses over the second one, or over transmission of both viruses simultaneously. This constraint was relaxed in plants, when transmission of TSWV and INSV occurred sequentially, demonstrating that plants serve as orthotospovirus permissive hosts, while thrips serve as a bottleneck. Viral fitness, as measured by virus replication, transmission, and competition with other viral strains, is not well studied in mixed infection. Our study looks at the success of transmission during mixed infection of orthotopoviruses, enhancing the understanding of orthotospovirus epidemiology and evolution.

Susceptibilities of Candidatus Liberibacter asiaticus-infected and noninfected Diaphorina citri to entomopathogenic fungi and their detoxification enzyme activities under different temperatures

Some entomopathogenic fungi species, Isaria fumosorosea, and Hirsutella citriformis were found to be efficient against the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). However, the susceptibility to these fungi increases when the psyllid infected with Candidatus Liberibacter asiaticus (Las), which is transmitted by D. citri and causes citrus greening disease. In this study, we examined the Las-infected and Las-uninfected D. citri susceptibility to entomopathogenic fungi at different temperature regimes (5-40°C). When D. citri adults exposed to cold temperature (5°C), they showed less susceptibility to entomopathogenic fungi as compared with control (27°C). Irrespective of infection with Las, a significantly positive correlation was observed between temperature and percentage mortality caused by different isolates of I. fumosorosea, 3A Ifr, 5F Ifr, PS Ifr, and H. citriformis isolates, HC3D and 2H. In contrast, a significantly negative correlation was found between temperature and percentage mortality for 3A Ifr for both Las-infected and Las-uninfected psyllids. Detoxification enzymes, Glutathione S-transferase levels in D. citri showed a negative correlation, whereas cytochrome P450 and general esterase levels were not correlated with changes in temperature. These findings revealed that detoxification enzymes and general esterase levels are not correlated with altered susceptibility to entomopathogenic fungi at the different temperature regimes. Conclusively, temperature fluctuations tested appear to be a significant factor impacting the management strategies of D. citri using entomopathogenic fungi.

Imidacloprid Pesticide Regulates Gynaikothrips uzeli (Thysanoptera: Phlaeothripidae) Host Choice Behavior and Immunity Against Lecanicillium lecanii (Hypocreales: Clavicipitaceae)

We attempted to develop an efficient management strategy against gall thrips (Gynaikothrips uzeli Zimmermann (Thysanoptera: Phlaeothripidae)) via the combined application of a systemic insecticide (imidacloprid) and an entomopathogenic fungus (Lecanicillium lecanii Zimmerman (Hypocreales: Clavicipitaceae)). The attraction of G. uzeli to Ficus microcarpa volatiles after imidacloprid treatment was weaker than for untreated plants, which could be due to modulation of volatile metabolite profiles by imidacloprid. The toxicity of L. lecanii against nymph and adult thrips was much higher for those that fed on plants treated with a 50% lethal concentration (LC50) of imidacloprid than for the controls. Phenoloxidase (PO) activity was significantly inhibited in treated G. uzeli, while hemocyte abundances were not different in treated and healthy individuals. Thus, imidacloprid impacted the PO-related humoral immunity of G. uzeli, but not their cellular immunity. Overall, F. microcarpa treated with imidacloprid at LC50 concentrations exhibited volatile profiles that decreased the attraction of G. uzeli and also indirectly increased the pathogenicity of L. lecanni by inhibiting the humoral immunity of gall thrips. The results reported here suggest that combined application of imidacloprid and L. lecanii could be used as a new integrated control strategy against gall thrips.

Genomic Analysis of Terpene Synthase Family and Functional Characterization of Seven Sesquiterpene Synthases from Citrus sinensis

Citrus aroma and flavor, chief traits of fruit quality, are derived from their high content in essential oils of most plant tissues, including leaves, stems, flowers, and fruits. Accumulated in secretory cavities, most components of these oils are volatile terpenes. They contribute to defense against herbivores and pathogens, and perhaps also protect tissues against abiotic stress. In spite of their importance, our understanding of the physiological, biochemical, and genetic regulation of citrus terpene volatiles is still limited. The availability of the sweet orange (Citrus sinensis L. Osbeck) genome sequence allowed us to characterize for the first time the terpene synthase (TPS) family in a citrus type. CsTPS is one of the largest angiosperm TPS families characterized so far, formed by 95 loci from which just 55 encode for putative functional TPSs. All TPS angiosperm families, TPS-a, TPS-b, TPS-c, TPS-e/f, and TPS-g were represented in the sweet orange genome, with 28, 18, 2, 2, and 5 putative full length genes each. Additionally, sweet orange β-farnesene synthase, (Z)-β-cubebene/α-copaene synthase, two β-caryophyllene synthases, and three multiproduct enzymes yielding β-cadinene/α-copaene, β-elemene, and β-cadinene/ledene/allo-aromandendrene as major products were identified, and functionally characterized via in vivo recombinant Escherichia coli assays.