Behavioral effects of different attractants on adult male and female oriental fruit moths, Grapholita molesta

A meta-analytic investigation of the potential for plant volatiles and sex pheromones to enhance detection and management of Lepidopteran pests

Effective early detection, monitoring and management methods are critical for reducing the impacts of insect pests in agriculture and forestry. Combining host plant volatiles with sex pheromones could enhance trapping methodologies, whilst the use of non-host volatiles could improve the effectiveness of pest management through repellency effects. In this meta-analysis approach, we analysed 51 studies that used electroantennograms (EAG), wind tunnels and/or field traps to evaluate the antennal and behavioural responses of Lepidoptera to sex pheromones combined with attractant or repellent plant volatiles. Proposed attractant plant volatiles had a positive association with female Lepidoptera responses to sex pheromone, but effects on males were highly variable, with unexpected repellency reported in some studies. Proposed repellent plant volatiles were significantly or near-significantly negatively associated with male attraction to sex pheromones but were scarcely studied. Sub-group analysis identified that male responses to sex pheromone were reduced when the dose of attractant plant volatile relative to sex pheromone was increased. Green-leaf volatiles were associated with the strongest positive effects for males in field traps. Multiple-compound attractant plant volatile blends were less effective than single compounds in field studies. Our analysis demonstrates, (i) the potential value of combining host plant volatiles with sex pheromones to capture females rather than only males, (ii) the importance of identifying appropriate host plant volatiles and optimal relative doses, and (iii) the potential for non-host plant volatile use in pest management strategies.

Male and Female Tortricid Moth Response to Non-Pheromonal Semiochemicals

In eastern North America, apple orchards are often attacked by several species of tortricid moths (Lepidoptera), including Cydia pomonella, Grapholita molesta, Argyrotaenia velutinana, and Pandemis limitata. Sex pheromones are routinely used to monitor male moth populations. Adding plant volatiles to monitoring traps could increase the capture of moths of both sexes and improve the effectiveness of mating disruption systems. This study sought to quantify the attraction of adults of four tortricid moth species to five olfactory treatments, namely (1) Pherocon® CM L2-P, (2) Pherocon Megalure CM 4K Dual® (=Megalure), (3) Megalure + benzaldehyde, (4) TRE 2266 (linalool oxide + (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT)), and (5) TRE 2267 (linalool oxide + DMNT + benzaldehyde), in non-mating disrupted commercial apple orchards in Massachusetts. The commercial lure Megalure was attractive to both sexes of G. molesta and C. pomonella. The addition of benzaldehyde to TRE 2266 or to Megalure significantly increased the capture of male G. molesta during the mid and late season of 2021. Only when benzaldehyde was added to TRE 2266 did the latter lure attract P. limitata in 2020 and 2021. The greatest number of tortricid moths (all four species combined) was captured by TRE 2267. This finding highlights the opportunity to enhance the attractiveness of a commercial lure through the addition of benzaldehyde, an aromatic compound, to Megalure. The potential of these additional volatiles to detect moths in a mating-disrupted orchard and/or remove female moths as a component of a management system is discussed.

Spodoptera litura larvae are attracted by HvAV-3h-infected S. litura larvae-damaged pepper leaves

BACKGROUND

Herbivore-induced plant volatiles (HIPVs) are important self-defense outputs of pepper plants to resist insect pests. Ascoviruses are pathogenic to the larvae of most lepidopteran vegetable pests. However, whether Heliothis virescens ascovirus 3h (HvAV-3h)-infected Spodoptera litura larvae can change pepper leaf HIPVs is not well understood.

RESULTS

Spodoptera litura larvae preferred S. litura-infested leaves, and this preference was stronger with longer duration of S. litura infestation. In addition, S. litura larvae significantly chose pepper leaves damaged by HvAV-3h-infected S. litura over the healthy pepper leaves. Results also showed that S. litura larvae preferred leaves mechanically damaged and treated with oral secretions from HvAV-3h infected-S. litura larvae in a simulation test. We captured the volatiles emitted by leaves under six treatments. Results showed that the volatile profile changed with the different treatments. Testing of volatile blends, prepared to the proportion released showed that the blend from simulated HvAV-3h-infected S. litura larvae-damaged plants was the most attractive to S. litura larvae. Further, we also found that some of the compounds significantly attracted S. litura larvae at specific concentrations.

CONCLUSION

HvAV-3h-infected S. litura can alter the release of HIPVs in pepper plants and thus become more attractive to S. litura larvae. We speculate that this may be due to alterations in the concentration of some compounds (such as geranylacetone and prohydrojasmon) affecting the behavior of S. litura larvae. © 2023 Society of Chemical Industry.

Repellence or attraction: secondary metabolites in pepper mediate attraction and defense against Spodoptera litura

BACKGROUND

Resistance to insect pests is an important self-defense characteristic of pepper plants. However, the resistance of different pepper cultivars to Spodoptera litura larvae, one of the main insect pest species on pepper, is not well understood.

RESULTS

Among seven pepper cultivars evaluated, cayenne pepper 'FXBX' showed the highest repellency to third instar S. litura larvae, Chao tian chili pepper 'BLTY2' showed the lowest repellency. Plant volatiles (1-hexene, hexanal, β-ionone, (E,E)-2,6-nonadienal, and methyl salicylate) affected host selection by S. litura. Among these, 1-hexene, hexanal, and β-ionone at concentrations naturally-released by pepper leaves were found to repel S. litura. Interestingly, S. litura larvae fed on the larva-attracting pepper cultivar, (BLTY2) had an extended developmental period, which was about 13 days longer than larvae fed on FXBX. Besides, the survival rate of larvae fed on BLTY2 was 22.5 ± 0.0%, indicating that the leaves of BLTY2 can kill S. litura larvae. Correlation analysis showed that larval survival rate, emergence rate, female adult longevity, and pupal weight were positively correlated with the vitamin C, amino acids, protein, cellulose, and soluble sugar contents, but were negatively correlated with wax and flavonoids contents.

CONCLUSION

We identified two different modes of direct defense exhibited by pepper cultivars against S. litura. One involves the release of repellent volatiles to avoid been fed on (FXBX cultivar). The other involves the inhibition of the growth and development or the direct killing of S. litura larvae which feeds on it (BLTY2 cultivar). © 2022 Society of Chemical Industry.

Antibiotic Treatment Reduced the Gut Microbiota Diversity, Prolonged the Larval Development Period and Lessened Adult Fecundity of Grapholita molesta (Lepidoptera: Tortricidae)

Grapholita molesta, the oriental fruit moth, is a serious pest of fruit trees with host transfer characteristics worldwide. The gut microbiota, which plays a crucial part in insect physiology and ecology, can be influenced by many elements, such as antibiotics, temperature, diet, and species. However, the effects of antibiotics on G. molesta gut microbiota are still unclear. In this study, we selected five common antibiotic agents to test the inhibition of G. molesta gut microbiota, and found ciprofloxacin shown the best antibacterial activity. After feeding 1 μg/mL of ciprofloxacin, the relative abundance of Actinobacteria and Cyanobacteria decreased significantly, while that of Firmicutes and Bacteroidetes increased. PICRUSt2 analysis indicated that most functional prediction categories were enriched in the G. molesta gut, including amino acid transport and metabolism, translation, ribosomal structure and biogenesis, carbohydrate transport and metabolism, transcription, cell wall/membrane/envelope biogenesis, and energy production and conversion. Finally, ciprofloxacin feeding significantly affected larval growth, development, and reproduction, resulting in prolonged larval development duration, shortened adult longevity, and significantly decreased single female oviposition and egg hatchability. In addition, we isolated and purified some culturable bacteria belonging to Proteobacteria, Firmicutes, Actinobacteria, and cellulase-producing bacteria from the G. molesta midgut. In brief, our results demonstrate that antibiotics can have an impact on G. molesta gut bacterial communities, which is beneficial for host growth and development, as well as helping female adults produce more fertile eggs. These results will thus provide a theoretical reference for developing new green control technology for G. molesta.

Plant Volatile Compounds of the Invasive Alligatorweed, Alternanthera philoxeroides (Mart.) Griseb, Infested by Agasicles hygrophila Selman and Vogt (Coleoptera: Chrysomelidae)

Plants release a variety of volatiles and herbivore-induced plant volatiles (HIPVs) after being damaged by herbivorous insects, which play multiple roles in the interactions with other plants and insects. Agasicles hygrophila Selman and Vogt (Coleoptera: Chrysomelidae) is a monophagous natural enemy and an effective biocontrol agent for Alternanthera philoxeroides (Mart.) Griseb. Here, we reported differences among the volatiles of A. philoxeroides by solid phase microextraction (SPME) using a gas chromatography-mass spectrometer (GC-MS). We compared the volatile emission of: (1) clean plants (CK); (2) A. philoxeroides plants with mechanical damage treatment (MD); and (3) A. philoxeroides plants infested with A. hygrophila 1st, 2nd, and 3rd larvae and female and male adults. A total of 97 volatiles were recorded, of which 5 occurred consistently in all treatments, while 61 volatiles were only observed in A. philoxeroides infested by A. hygrophila, such as trans-nerolidol, (E)-β-farnesene, and (3E,7E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (E, E-TMTT), etc. Among the 97 volatile compounds, 37 compounds belong to alkenes, 29 compounds belong to alkanes, and there were 8 esters, 8 alcohols and 6 ketones. Orthogonal partial least squares-discrimination analysis (OPLS-DA) showed that the different treatments were separated from each other, especially insect feeding from CK and MD treatments, and 19 volatiles contributed most to the separation among the treatments, with variable importance for the projection (VIP) values > 1. Our findings indicated that the alligatorweed plants could be induced to release volatiles by different stages of A. hygrophila, and the volatile compounds released differ quantitatively and qualitatively. The results from this study laid an important foundation for using volatile organic compounds (VOCs) and HIPVs of alligatorweed to improve the control effect of A. hygrophila on A. philoxeroides.

Corazonin signaling modulates the synthetic activity of male accessory gland in Grapholita molesta

Although neuropeptide corazonin (Crz) has been identified in numerous insect species, the research about its function in regulation of reproduction is still in its infancy. Herein, we characterized the Crz (GmolCrz) and its receptor (GmolCrzR) to investigate their reproductive function in Grapholita molesta. Both molecular docking result and cell-based receptor activity assay showed that GmolCrz could interact with GmolCrzR. Additionally, spatial expression patterns of GmolCrz and GmolCrzR in males were evaluated. Knockdown of GmolCrz or GmolCrzR significantly lengthened copulation duration and decreased fertility in males. In these males, we found that the production of sperm was normal, while the content of accessory gland proteins (Acps) in the accessory gland (AG) was strongly diminished. Furthermore, knockdown of GmolCrz or GmolCrzR in males had no effect on sperm and Acps transfer to females. RNA-seq and gene expression analyses further confirmed that genes involved in serine-type endopeptidase activity were significantly downregulated in the AG upon GmolCrzR knockdown. Finally, sperm activation assays demonstrated that this process was disrupted in the spermatophore of females mated with GmolCrz or GmolCrzR knockdown males, which may cause the decreased fertility in males. Our findings provide new insights into the functions of Crz signaling in a Lepidopteran insect.

A closer look at sex pheromone autodetection in the Oriental fruit moth

Female moths emit sex pheromone to attracts males, and although they are not attracted to their own sex pheromone, they appear to detect it as it affects their behavior. In order to elucidate the mechanism of pheromone "autodetection" we compared responses of olfactory receptor neurons (ORNs) of male and female Grapholita molesta, a species with reported pheromone autodetection. Two concentrations of the major (Z8-12:Ac) and minor (E8-12:Ac) sex pheromone components, a plant-volatile blend containing methyl salicylate, terpinyl acetate and (E)-β-farnesene, and the male-produced hair-pencil (i.e., courtship) pheromone (ethyl trans-cinnamate) were tested in 45 male and 305 female ORNs. Hierarchical cluster analysis showed radically different peripheral olfactory systems between sexes that could be linked to their specific roles. In males 63% of the ORNs were tuned specifically to the major or minor female sex pheromone components, and 4% to the plant volatile blend, while the remaining 33% showed unspecific responses to the stimulus panel. In females 3% of the ORNs were specifically tuned to the male hair-pencil pheromone, 6% to the plant volatile blend, 91% were unspecific, and no ORN was tuned their own sex pheromone components. The lack of sex pheromone-specific ORNs in females suggests that they are not able to discriminate pheromone blends, and thus pheromone autodetection is unlikely in this species. We discuss our results in the context of the methodological limitations inherent to odor stimulation studies.

Chinese Cabbage Changes Its Release of Volatiles to Defend against Spodoptera litura

Simple Summary

Biological control is an important direction for pest control in the future, and chemical ecology is an indispensable part of biological control. Therefore, we tested the selection of Spodoptera litura and parasitic wasps on the volatiles of different treatments of cabbage and collected and analyzed the volatiles of different treatments of cabbage. This study found that cabbage was fed by Spodoptera litura to produce volatiles to avoid Spodoptera litura while also attracting Microplitis similis. As a result, some compounds were found to be related to the behavior of Spodoptera litura and Microplitis similis. These results provide a theoretical basis for searching for biological control resources and chemical control.

Abstract

Plants respond to herbivorous insect attacks by releasing volatiles that directly harm the herbivore or that indirectly harm the herbivore by attracting its natural enemies. Although the larvae of Spodoptera litura (the tobacco cutworm) are known to induce the release of host plant volatiles, the effects of such volatiles on host location by S. litura and by the parasitoid Microplitis similis, a natural enemy of S. litura larvae, are poorly understood. Here, we found that both the regurgitate of S. litura larvae and S. litura-infested cabbage leaves attracted M. similis. S. litura had a reduced preference for cabbage plants that had been infested with S. litura for 24 or 48 h. M. similis selection of plants was positively correlated with the release of limonene; linalool and hexadecane, and was negatively correlated with the release of (E)-2-hexenal and 1-Butene, 4-isothiocyanato. S. litura selection of plants was positively correlated with the release of (E)-2-hexenal, 1-Butene, 4-isothiocyanato, and decanal, and was negatively correlated with the release of limonene, nonanal, hexadecane, heptadecane, and octadecane. Our results indicate that host plant volatiles can regulate the behavior of S. litura and M. similis.

Enantioselective Synthesis of the Sex Pheromone of Lichen Moth, Miltochrista calamine, and Its Diastereomer

The synthesis of a Miltochrista calamine sex pheromone and its diastereomer has been developed. The key steps of the synthetic approach involved Evans’ chiral auxiliaries and the addition of alkyne to aldehyde, which were firstly applied to prepare this sex pheromone and its diastereomer. The synthetic sex pheromone could be used to trap insects and study physiological and ecological questions of the lichen moth.

Effect of sublethal Spirotetramat on host locating and parasitic behavior of Encarsia formosa Gahan

BACKGROUND

The use of chemical insecticides to control Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) is widespread, although it might exert a sublethal effect on its dominant parasitoid, Encarsia formosa Gahan (Hymenoptera: Aphelinidae). To investigate the sublethal effect of spirotetramat on E. formosa, we observed the ability of E. formosa to locate and handle the host, oviposit and preen after exposure to sublethal concentrations of spirotetramat.

RESULTS

After exposure to spirotetramat at LC₅₀ , the response time of E. formosa to the volatile reached 223.40 s and was significantly prolonged. Only 56.44% of the wasps were attracted by the volatile and the insect crawled the slowest among all of the treatments. The averages of oviposition posture adopted and host handled by each E. formosa in 1 h decreased significantly to 1.79 and 1.27, respectively. At the sublethal concentration of LC₁₀ , 94.59% of the wasps were attracted by the volatile and the insect crawled the fastest. The average of host handled by each E. formosa was 3.92, and the frequency of drumming while walking and drumming the host was 12.34 times per second and 12.30 times per second, respectively, demonstrating a significant acceleration in these abilities.

CONCLUSION

These findings demonstrate that spirotetramat induced hormesis in E. formosa on exposure to its LC₁₀ concentration and accelerated its host locating, host handling and frequency of antennae drumming. These findings could assist in balancing the chemical and biological control of B. tabaci and enhancing the efficacy of E. formosa as a biocontrol agent. © 2021 Society of Chemical Industry.

Effects of operational sex ratio, mating age, and male mating history on mating and reproductive behavior in Grapholita molesta

The short-lived polygamous moth Grapholita molesta (Busck) is an important fruit pest worldwide. Trapping males by synthetic female sex pheromones is not an effective reproductive control strategy. It is important to improve this technology by understanding the mating system of G. molesta. This study investigated mating opportunities and fertile egg production by altering the operational sex ratio, mating age, and male mating history in repeated single mating and multiple mating in the two sexes. Our results showed that the mating and reproductive parameters of virgin males were affected by the number and age of virgin females. Males preferred a female number ≤three-fifths of the male number or ≤2-day-old females, while they discriminated against a female number ≥three times of the male number or ≥5-day-old females. On the other hand, the mating and reproductive parameters of virgin females were affected by repeated single mating and especially multiple mating under different male mating histories. Females preferred once-mated males and discriminated against virgin males. These results indicated that mating systems including more and older virgin females for virgin males and different virgin males for virgin females may be suitable for suppressing G. molesta populations. Hence, these results revealed that preventing mating of virgin adults by synthetic female sex pheromones should be most effective in controlling G. molesta.

Evidence of the Involvement of a Plus-C Odorant-Binding Protein HparOBP14 in Host Plant Selection and Oviposition of the Scarab Beetle Holotrichia parallela

Simple Summary

The scarab beetle Holotrichia parallela is a serious underground pest and causes serious damages in China to a variety of crops. To reduce the use of pesticides, insect olfactory proteins attract more and more attention in the development of pollution-free control agents in plant protection. In this study, we evaluate the molecular mechanism in the scarab beetle to detect oviposition cues. We clone a leg biased gene HparOBP14 which encodes for an odorant-binding protein of the scarab beetle and demonstrate its involvement in binding, electrophysiological, and behavioral responses to the oviposition chemicals by the knockdown of HparOBP14 expression using RNA interference technique. Our study provides a strong theoretical basis for the development of environmentally acceptable strategies for H. parallela control.

Abstract

Holotrichia parallela is one of the agriculturally important scarab beetle pests in China. In this study, HparOBP14 was cloned, which is the most abundantly expressed among the OBP genes in the legs of female H. parallela adults. Sequence comparison and phylogenetic analysis showed that HparOBP14 has a Plus-C structure motif. The expression profile analysis revealed that HparOBP14 expression was the highest in the female antennae and then in the legs. The fluorescence competitive binding experiment of the recombinant HparOBP14 protein showed that HparOBP14 had an affinity with 6-methyl-5-heptene-2-one (plant volatile), 3-methylindole, p-cymene, methanol, formaldehyde, α-pinene, and geraniol (organic fertilizer volatile). Knockdown HparOBP14 expression decreased significantly the EAG response of the injected female adults to p-cymene, methanol, formaldehyde, α-pinene, and geraniol. Similarly, the injected female adults were significantly less attracted to geraniol and methanol. Therefore, HparOBP14 might bind organic matter volatiles during oviposition. These results are not only helpful to analyze the olfactory recognition mechanism of female adult H. parallela when choosing suitable oviposition sites, but also to provide target genes for green prevention and control of H. parallela in the future.