EAG Responses Research Articles

Pheromone antagonism in Plu tella xylostella (Linnaeus) by sex pheromones of two sympatric noctuid moths.

Responses to sex pheromones are commonly antagonized by pheromone components of closely related species. Pheromone antagonism has not been widely explored for phylogenetically distant species that have completely different pheromone components. Yet, pheromone components of sympatrically occurring species may also interfere with each other even if these species are distantly related. Here, the effects of heterospecific pheromones on electrophysiology (electroantennogram, EAG) and behavioral responses were tested on the diamondback moth Plutella xyloslella (Plutellidae) and two sympatric noctuid moth species, Spodoptera litura and Spodoptera exigua, whose larvae also feed on Brassica crops. The sex pheromone blend of P. xyloslella, and its components, did not elicit EAG responses in males of the two noctuid species, while sex pheromone components of the noctuid moths elicited significant EAG responses in P. xyloslella males. In wind tunnel bioassays, both (Z, E)-9, 12-tetradecadienyl acetate (ZE-9,12-14:OAc) and (Z, E)-9, 11-tetradecadienyl acetate (ZE-9,11-14:OAc), sex pheromone components from the noctuid moths, inhibited the upwind flight behavior of P. xyloslella males toward an intraspecific pheromone odor source. In Brassica fields, sex pheromone lures of P. xyloslella did not influence trap catches of the noctuid moths, while P. xyloslella pheromone lures baited with either ZE-9,11-14:OAc or ZE-9,12-14:OAc decreased trap catches of P. xyloslella males in a dose-dependent manner. Trap catches of P. xylostella males were also affected by the proximity of ZE-9,11-14:OAc or ZE-9,12-14:OAc to P. xylostella lures. The uni-directional pheromone antagonism by ZE-9,11-14:OAc and ZE-9,12-14:OAc suggests innovative semiochemical-based strategies for the management of P. xyloslella and other economically important pests in Brassica fields. © 2021 Society of Chemical Industry.

Development of a Phytochemical-Based Lure for the Dried Bean Beetle Acanthoscelides obtectus Say (Coleoptera: Chrysomelidae).

The dried bean beetle, Acanthoscelides obtectus, is an economically important, worldwide pest of legume crops including dry beans, Phaseolus vulgaris. Assessment of A. obtectus infestation levels in pre-harvest field crops and post-harvest granaries is difficult to achieve because there is no effective monitoring tool for early detection so that interventions can be deployed as needed. Because A. obtectus is a generic pollen and nectar feeder, we adopted an electrophysiological (EAG) screening approach, using the antennae of female A. obtectus to identify physiologically active, volatile phytochemicals, which could then be investigated for their attractiveness to A. obtectus in laboratory behavioral assays and preliminary field tests. Of the 27 compounds tested in EAG screening, 5 compounds, i.e., methyl anthranilate, methyl eugenol, benzyl alcohol, (RS)-lavandulol, and 2-phenylethanol, elicited stronger EAG responses than the standard (1-phenylethanol). In 4-arm olfactometer bioassays, female A. obtectus preferred the olfactometer arm containing the odor of either methyl anthranilate or benzyl alcohol compared to the solvent control. In preliminary field tests using these 2 compounds as a binary mixture, at least 5 times as many beetles were caught on baited traps compared to non-baited traps. The field data also suggested that benzyl alcohol was primarily responsible for the field activity of the blend. We hypothesize that the attraction of A. obtectus to the combined benzyl alcohol/methyl anthranilate and the single benzyl alcohol baits is connected to the species` nectar- and pollen-feeding behaviour and not to its intraspecific communication. To our knowledge, this is the first evidence that A. obtectus behavior in the field can be modified by the deployment of plant-derived semiochemicals.

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

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.

Electroantennogram and behavioral responses of Agrilus mali to the volatiles from Malus sieversii trees induced by pest and disease

Objective This study aims to explore the electroantennogram and behavioral responses of Agrilus mali to the volatiles from Malus sieversii trees in different damaged states to provide reference for the research and development of highly effective attractants. Method The volatiles were collected by using dynamic headspace adsorption from branches and limbs of M. sieversii trees. Result There are total of 46 volatile compounds in 9 categories has been obtained, including alcohols, lipids, aldehydes, alkanes, alkenes, ketones, terpenes, ethers and others. Compared with healthy branches, the relative contents of eicosane and pentadecane increased in A. mali damaged branches, while the relative contents of 8 volatiles such as butenol, 2-methylacrolein, heptadecane, heneicosane, cycloheptatriene, cyclohexanone, α-pinene and chamomile decreased. Fourteen compounds were added such as cis-3-hexenol, hexanal, decanal, nonanal, (+)-limonene etc. In Valsa mali damaged branches, pentadecane, heptadecane, 3,7-dimethyldecane, eicosane and α-pinene increased, and heneicosane, cyclohexanone, cycloheptatriene, azulene decreased. Twelve compounds were added such as cis-3-hexenol, butyl butyrate, hexanal, (+)-α-pinene, (+)-limonene, etc. Compared with the volatilides released from healthy limbs, the relative contents of cis-3-hexenol, α-pinene, (−)-α-pinene and camphene were increased in A. mali damaged limbs, and hexanal, cycloheptane, β-pinene, cycloheptatriene, azulene contents decreased. Seventeen compounds were added such as 3-octene-2-alcohol, butyl butyrate, decanal pentadecane, (+)-aromadendrene, etc. In Valsa mali damaged limbs, hexanal increased, and cis-3-hexenol, acrolein, cyclohexanone, α-pinene, (−)-α-pinene, β-pinene and azulene decreased. Eleven compounds were added such as benzaldehyde, pentadecane, dipentene, etc. EAG responses and behaviour of A. mali towards volatiles released by host were tested. The results showed that strong EAG reactants could be produced in the antennae of male and female adults of A. mali, these compounds were (−)-α-pinene, nonanal, (+)-α-pinene, benzaldehyde, decanal, butyl acrylate. A. mali were attracted by (−)-α-pinene, α-pinene, (+)-β-pinene, β-pinene, decanal, nonanal in the behavior bioassay. Conclusion According to the results of EAG responses and behavioral orientation, the (−)-a-pinene, nonanal and decanal had good attraction to the adult of Agrilus mali.[Ch, 1 fig. 3 tab. 27 ref.]

An Orphan Pheromone Receptor Affects the Mating Behavior of Helicoverpa armigera.

The Lepidoptera is the second largest insect order, which has the most extensive knowledge of sex pheromones and mechanisms of pheromone communication since the identification of the first insect pheromone in Bombyx mori. In the past 15 years, pheromone receptors have been identified and functionally characterized in many moth species. HarmOR14 is a typical pheromone receptor of Helicoverpa armigera which showed no response to the tested pheromones in Xenopus oocyte expression system, but its orthologous gene in Heliothis virescens, HvirOR14 could be activated by pheromones in the same expression system. To assess the possible functions of OR14 in vivo, in this study, we knocked out this gene using CRISPR/Cas9 system and compared the mating behaviors and EAG response to pheromones between the wild type and mutant strains. Our results showed that OR14 mutants did not affect the mating rate or the EAG response to pheromones but could prolong the mating duration and change the mating time in undefined manners, which extends our understanding to this kind of pheromone receptors.

The cotton bollworm endoparasitoid Campoletis chlorideae is attracted by cis-jasmone or cis-3-hexenyl acetate but not by their mixtures

Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae) is an important larval endoparasitoid of the cotton bollworm Helicoverpa armigera (Hubner). A better understanding of herbivore-induced plant volatiles (HIPVs) employed by C. chlorideae to locate hosts will contribute towards the biological control of this notorious crop pest. In this study, we first investigated the electrophysiological and behavioral responses of C. chlorideae to 19 volatile compounds emitted by herbivore-infested plants. Eleven odorants induced EAG responses of C. chlorideae, while only two compounds, cis-jasmone and cis-3-hexenyl acetate, were attractive to the parasitoid in Y-tube olfactometer assays. Next, we used two- and four-choice tests in cage settings to investigate the parasitism rate of H. armigera larvae by C. chlorideae on tobacco plants treated with different doses of cis-jasmone, cis-3-hexenyl acetate, and their mixtures. Results showed that the parasitism rate of H. armigera was significantly higher on the plants treated with cis-jasmone or cis-3-hexenyl acetate, and their optimal dose for both compounds was 1 mg. However, the mixtures of cis-jasmone and cis-3-hexenyl acetate did not increase H. armigera parasitism rate by C. chlorideae when compared with control groups. Our results indicate that the single compounds cis-jasmone and cis-3-hexenyl acetate, at certain doses, enhance parasitic efficiency of C. chlorideae, but their mixtures negate this effect. These results will help us in the exploitation of C. chlorideae as biological control agent to reduce the populations of H. armigera.

Three Chemosensory Proteins Involved in Chemoreception of Oedaleus asiaticus (Orthopera: Acridoidea).

Chemosensory proteins (CSPs) are thought to play roles in the insect olfactory system by binding and carrying hydrophobic odorants across the aqueous sensillar lymph. The band-winged grasshopper, Oedaleus asiaticus Bei-Bienko, is one of the most important grasshopper pests in northern China, but there is little information about its olfactory system. In order to investigate the olfactory functions of CSPs in this pest, three CSP genes (OasiCSP4, OasiCSP11 and OasiCSP12) were expressed in Escherichia coli, and the binding affinities of the three recombinant CSP proteins were measured for 16 volatiles from the host plant (Stipa krylovii), fecal material and body of live adult O. asiaticus using fluorescence competitive binding assays. To further verify their olfactory functions, RNA interference (RNAi) and electrophysiological recording were conducted. The three recombinant proteins displayed different degrees of binding to various volatiles in ligand-binding assays, with OasiCSP12 having higher binding affinities for more volatiles than OasiCSP4 and OasiCSP11. OasiCSP12 exhibited strong binding affinities (Ki < 20 μΜ) for five host plant volatiles and one volatile from the live body of adult O. asiaticus. The transcript levels of the three OasiCSP genes were significantly lower after silencing the individual genes by RNAi, which in turn reduced the EAG responses in adults of both sexes to most tested compounds. Our study indicates that these three OasiCSPs are involved in the detection of volatile semiochemicals, and may play important roles in finding host plants and in aggregation in O. asiaticus.

Identification and field verification of aggregation-sex pheromone from the predaceous bug, Arma chinensis

Arma chinensis is a predaceous insect species that can effectively suppress a wide range of agricultural and forest insect pests in the orders Lepidoptera, Coleoptera, Hymenoptera and Hemiptera in Northeast Asia. Adult A. chinensis males produce an aggregation-sex pheromone from dorsal abdominal glands and artificial aggregation-sex pheromone can attract adults of both sexes. The aggregation-sex pheromone consists of (E)-2-hexenal, (E)-2-hexen-1-ol, benzaldehyde and benzyl alcohol. Both antennae and proboscises of A. chinensis females and males responded to components from male dorsal abdominal gland extracts. (E)-2-hexenal and benzaldehyde elicited significantly higher EAG responses than those with (E)-2-hexen-1-ol and benzyl alcohol. Benzyl alcohol elicited the weakest EAG responses, although benzyl alcohol was the most abundant of the four major components in male dorsal abdominal gland extracts. A field bioassay using trap catches demonstrated that (E)-2-hexenal and benzyl alcohol were key components of the pheromone for catching conspecific adults. Single pheromone components were the least attractive to A. chinensis in the field.

CRISPR/Cas9 mediated gene knockout reveals a more important role of PBP1 than PBP2 in the perception of female sex pheromone components in Spodoptera litura

Three different pheromone binding proteins (PBPs) can typically be found in the sensilla lymph of noctuid moth antennae, but their relative contributions in perception of the sex pheromone is rarely verified in vivo. Previously, we demonstrated that SlitPBP3 plays a minor role in the sex pheromone detection in Spodoptera litura using the CRISPR/Cas9 system. In the present study, the roles of two other SlitPBPs (SlitPBP1 and SlitPBP2) are further verified using the same system. First, by co-injection of Cas9 mRNA/sgRNA into newly laid eggs, a high rate of target mutagenesis was induced, 51.5% for SlitPBP1 and 46.8% for SlitPBP2 as determined by restriction enzyme assay. Then, the homozygous SlitPBP1 and SlitPBP2 knockout lines were obtained by cross-breeding. Finally, using homozygous knockout male moths, we performed electrophysiological (EAG recording) and behavioral analyses. Results showed that knockout of either SlitPBP1 or SlitPBP2 in males decreased EAG response to each of the 3 sex pheromone components (Z9,E11-14:Ac, Z9,E12-14:Ac and Z9-14:Ac) by 53%, 60% and 63% (for SlitPBP1 knockout) and 40%, 43% and 46% (for SlitPBP2 knockout), respectively. These decreases in EAG responses were similar among 3 pheromone components, but were more pronounced in SlitPBP1 knockout males than in SlitPBP2 knockout males. Consistently, behavioral assays with the major component (Z9,E11-14:Ac) showed that SlitPBP1 knockout males responded in much lower percentages than SlitPBP2 knockout males in terms of orientation to the pheromone, along with reduction in close range behaviors such as hairpencil display and mating attempt. Taken together, this study provides direct functional evidence for the roles of SlitPBP1 and SlitPBP2, as well as their relative importance (SlitPBP1 > SlitPBP2) in the sex pheromone perception. This information is valuable in understanding mechanisms of sex pheromone perception and may facilitate the development of PBP-targeted pest control techniques.

The choice between flowers of closely related plant species by generalist pollinator: identification of relevant VOCs

False blister beetles of the genus Oedemera (Coleoptera: Oedemeridae) are known as generalist pollinators of many plant species, but their mutualistic interactions are still insufficiently explored. The aim of the study was to identify the floral compounds emitted by sympatric and simultaneously co-flowering strawberry species that could serve for Oedemera beetles as olfactory cues of suitable flowers. In the test locality, flowers of Fragaria vesca and Fragaria viridis were visited by Oedemera lurida and Oedemera virescens beetles. O. lurida preferred flowers of F. viridis to those of F. vesca, whereas O. virescens tended to prefer F. vesca to F. viridis. GC-EAD analysis revealed that O. lurida perceived three compounds of F. vesca and four compounds of F. viridis flowers. Among these, nonanal, 2-phenylacetaldehyde and an unidentified compound (UC1) were common to both strawberries, while the amount of one compound (1,4-dimethoxybenzene) required to elicit an EAG response was sufficient in F. viridis, but not in F. vesca. Our results suggest that O. lurida are capable of choosing between flowers of the two strawberries based on VOCs’ with 1,4-dimethoxybenzene as a relevant key component. O. virescens responded to eight compounds present in F. vesca flowers. The flowers contained three compounds EAG-active towards O. lurida and O. virescens (nonanal, 2-phenylacetaldehyde, UC1) and five compounds EAG-active towards O. virescens only (acetic acid, decanal, (E)-non-2-enal, linalool, and UC2). In F. vesca and F. viridis flower extracts as well as headspaces, the identified compounds differed qualitatively only. (E)-Non-2-enal and acetic acid were recorded for the first time in Fragaria. Local specialization of Oedemera beetles in flower visiting was proved and relevant VOCs were identified.

A female attractant for the blue gum chalcid, Leptocybe invasa (Hymenoptera: Eulophidae), from host plant (DH 201-2: Eucalyptus grandis × Eucalyptus tereticornis)

The blue gum chalcid, Leptocybe invasa, is a severe insect pest of Eucalyptus trees leading to gall formation, stunting, leaf deformation, and death in cases, China. In the previous studies, we found that the Eucalyptus hybrid, DH 201-2 (Eucalyptus grandis × Eucalyptus tereticornis), is highly preferred to L. invasa larvae and adults, but its mechanism has not been fully understood. In the present study, we investigated the volatile organic compounds (VOCs) from DH 201-2 that attract L. invasa. Volatiles were collected from fresh young leaves and identified with gas chromatography–mass spectrometry (GC–MS) and gas chromatography–electroantennogram detection (GC–EAD). The attraction of identified volatiles to L. invasa was then measured under laboratory and field conditions. Two EAD-active compounds, gamma-terpinene and Limonene, were identified. In the dose–response experiments, we found that the EAG response to L. invasa was enhanced with the increased concentration of EAD-active compounds, and gamma-terpinene showed the stronger EAG response than Limonene. Both four-arm olfactometer bioassays and field studies showed that the blend of gamma-terpinene and Limonene with a ratio of 8:2 significantly attracted more L. invasa as compared to other ratios. The potential use of these compounds in the control of L. invasa is ulteriorly discussed.

Molecular and Functional Characterization of Odorant Binding Protein 7 From the Oriental Fruit Moth Grapholita molesta (Busck) (Lepidoptera: Tortricidae).

Odorant-binding proteins (OBPs) are widely and abundantly distributed in the insect sensillar lymph and are essential for insect olfactory processes. The OBPs can capture and transfer odor molecules across the sensillum lymph to odorant receptors and trigger the signal transduction pathway. In this study, a putative OBP gene, GmolOBP7, was cloned using specific-primers, based on the annotated unigene which forms the antennal transcriptome of Grapholita molesta. Real-time PCR (qRT-PCR) analysis revealed that GmolOBP7 was highly expressed in the wings of males and the antennae of both male and female adult moths, while low levels were expressed in other tissues. The recombinant GmolOBP7 (rGmolOBP7) was successfully expressed and purified via Ni-ion affinity chromatography. The results of binding assays revealed that rGmolOBP7 exhibited a high binding affinity to the minor sex pheromone 1-dodecanol containing Ki of 7.48 μM and had high binding capacities to the host-plant volatiles, such as pear ester, lauraldehyde and α-ocimene. RNA-interference experiments were performed to further assess the function of GmolOBP7. qRT-PCR showed that the levels of mRNA transcripts significantly declined in 1 and 2 day old male and female moths, treated with GmolOBP7 dsRNA, compared with non-injection controls. The EAG responses of dsRNA-injected males and females to pear ester, as well as the EAG responses of dsRNA-injected males to 1-dodecanol, were significantly reduced compared to the GFP-dsRNA-injected and non-injected controls. We therefore infer that GmolOBP7 has a dual function in the perception and recognition of the host-plant volatiles and sex pheromones.

Electrophysiological Response of Dysdercus cingulatus (Fabricius) (Hemiptera: Pyrrhocoridae) to Cotton Plant Extracts and Other Host Related Compounds

Electroantennogram response from antennae of male and female, Dysdercus cingulatus (Fabricius) a cotton pest was recorded against hexane extracts of cotton plant (leaves, squares and bolls) as well as with identified synthetic volatile compounds. Different volatile compounds were identified from cotton plant part by gas chromatography–Mass spectrometer techniques. The males and females of D. cingulatus showed its characteristic EAG response to cotton extracts and to fifteen other synthetic (docosane, pentacosane, tetracontane, tricosane, hexatricontane, hexacosane, octatricontane, heneicosane, triacontane, hentriacontane, octadecane, dotriacontane, tetracosane, octacosanoic acid, eiocosanic acid) compounds. Statistically significant differences in EAG response were observed between both sexes. The responses were found to be dose-depended and maximum peak amplitude were recorded by heneicosane, hentriacontane, tricosane and hexatricontane. In female, the largest peak amplitudes were obtained from heneicosane, hentriacontane, tricosane and octatricontane, whereas heneicosane, triacontane, and octatricontane were found to evoke significantly different responses among males. Electroantennogram study of D. cingulatus has manifested the differential sensitivity of antennal receptors to these compounds.

Conspecific and Heterogeneric Lacewings Respond to (Z)-4-Tridecene Identified from Chrysopa formosa (Neuroptera: Chrysopidae).

Green lacewings (Chrysopidae) are predators of soft-bodied pest insects and are among the most important biological control agents in crop protection. Chrysopa spp. are of special importance since, unlike most green lacewing species, adults are also predatory. The current study was undertaken in search of Chrysopa formosa compounds with semiochemical activity. Using coupled gas chromatography-electroantennography (GC-EAG), head and thorax extracts of C. formosa elicited EAG responses to a compound subsequently identified by coupled GC/mass spectrometry, microchemistry, chemical synthesis and GC peak enhancement as (Z)-4-tridecene. In field experiments, this compound decreased attraction of adult C. formosa to (1R,4aS,7S,7aR)-nepetalactol and that of Chrysoperla carnea species-complex to a ternary floral lure, with the inhibitory effect found to be dose-dependent. Our results suggest that (Z)-4-tridecene may serve as a general warning signal among multiple green lacewing species. Perspectives for potential practical applications are discussed.

Elecroantennogram Responses of the Cherry Fruit Fly Rhαgoletis cerαsi (Diptera: Tephritidae) to Naturally Occurring Volatiles

EAG responses of the cherry fruit fly, Rhagoletis cerasi (Linne) (Diptera: Tephritidae) were recorded in response to seventy-eight generally occurring plant volatiles and male cherry fruit fly volatiles. The test compounds are representatives of three major classes of organic compounds, aldehydes, ketones, and monoterpenes. No differences were observed in the degree of response between males and females, Carbon-chain length, unsaturation, and position of functional groups all have significant effect on the magnitude of EAG response.

Electroantennogram responses from olfactory receptors in Dαcus oleαe

Substances found in Dacus oleae (Gmelin) (Diptera: Tephritidae) male or female flies which have been reported as pheromones, i.e. elicit some form of biological activity in laboratory or field bioassays, were tested with the electroantennogram technique (EAG). Substances of non-insect origin were also tested as possible pheromone candi­dates. All substances of insect or non-insect origin elicited an EAG response to both sexes of lab-cultured or wild insects but 1,7 dioxaspiro [5,5] undecane, the major pheromone component, has a lower response threshold value than all other compounds. At the maximum stimulus concentration the response to nonanal reaches a value higher than that elicited by all other compounds. EAG responses to various compounds, after receptor adaptation to the major pheromone compound and nonanal, showed that these two compounds are detected by different sets of receptors. Other comments on the sensitivity and specificity of antennal receptors are also presented.

What signals do herbivore-induced plant volatiles provide conspecific herbivores?

Herbivore-induced plant volatiles (HIPVs) have been opined as ‘indirect or direct defenses’ of plants and are extensively studied. In contrast, HIPVs may also indicate that plant defenses have been overcome by herbivores infesting the plant; however, studies on this aspect have so far received little attention. Using the interaction of Capsicum annum (Bell pepper) with its pest Scirtothrips dorsalis (Chilli thrips) as a model system, we studied the role of HIPVs in this selected insect–plant interaction. Multiple-choice olfactometer assays with headspace volatiles collected from different growth stages of un-infested C. annum plants represented by pre-flowering (PF), flowering (FL) and fruiting stages (FR) proved FR volatiles to be highly attractive to S. dorsalis. Further, FR plants were infested with S. dorsalis adults and HIPVs released by infested plants were collected and subjected to multiple-choice olfactometer bioassays. Thrips were significantly attracted to HIPVs than to headspace volatiles of un-infested FR plants or thrips body odour. Coupled GC-EAG with S. dorsalis and HIPVs or FR plant volatile revealed specific compounds that elicited an EAG response. Individual EAG-active compounds were less attractive to thrips, however, synthetic blends of EAG-active compounds at the ratio similar to headspace samples were found to be highly attractive. However, when given a choice between synthetic blends of HIPVs and FR, thrips were significantly attracted to synthetic blend of HIPVs. Our study provides empirical data on signals HIPVs may provide to conspecific herbivores and suggests that the role of HIPVs, mostly generalized as defense, may vary based on the interaction and must be studied closely to understand their ecological functions.

Antennal responses to volatile organic compounds in a stonefly

Notwithstanding their long antennae, especially in the adult stage, Plecoptera represent a poorly studied group as regards their sensory structures and their ability to perceive olfactory stimuli is so far totally unknown. A recent investigation on the antenna of Dinocras cephalotes revealed two kinds of putative olfactory sensilla (multiporous single walled sensilla and digitated double walled sensilla). The present electrophysiological study (electroantennography, EAG), in which male and female antennae of D. cephalotes (Plecoptera, Perlidae) have been stimulated with a set of generic odours belonging to different functional groups, shows that Plecoptera can perceive olfactory cues through their antennal sensilla. Indeed, although many chemicals did not elicit any response, high EAG activity has been recorded in response to pentanoic acid, propanal, butyric acid, propionic acid, isoamylamine and ammonia. The response was very similar in both sexes even if propanal elicited a response only in males. EAG dose-responses curves in both males and females showed that EAG responses were similar in males and females and generally increased in amplitude with increasing doses of the chemicals. Behavioural, neuroanatomical and molecular investigations on Plecoptera olfaction, could be particularly interesting not only to increase the knowledge of the adult stonefly behaviour but also to better understand the adaptation of the olfactory sensory system in aquatic insects moving from land to water.

Age influences the olfactory profiles of the migratory oriental armyworm mythimna separate at the molecular level

BackgroundThe oriental armyworm Mythimna separata (Walk) is a serious migratory pest; however, studies on its olfactory response and its underlying molecular mechanism are limited. To gain insights to the olfactory mechanism of migration, olfactory genes were identified using antennal transcriptome analysis. The olfactory response and the expression of olfactory genes for 1-day and 5-day-old moths were respectively investigated by EAG and RT-qPCR analyses.ResultsPutative 126 olfactory genes were identified in M. separata, which included 43 ORs, 13 GRs, 16 IRs, 37 OBPs, 14 CSPs, and 3 SNMPs. RPKM values of IR75d and 10 ORs were larger than co-receptors IR25a and ORco, and the RPKM value of PR2 was larger than that of other ORs. Expression of GR1 (sweet receptor) was higher than that of other GRs. Several sex pheromones activated evident EAG responses where the responses of 5-day-old male moths to the sex pheromones were significantly greater than those of female and 1-day old male moths. In accordance with the EAG response, 11 pheromone genes, including 6 PRs and 5 PBPs were identified in M. separate, and the expression levels of 7 pheromone genes in 5-day-old moths were significantly higher than those of females and 1-day-old moths. PR2 and PBP2 might be used in identifying Z11-16: Ald, which is the main sex pheromone component of M. separata. EAG responses to 16 plant volatiles and the expression levels of 43 olfactory genes in 1-day-old moths were significantly greater than that observed in the 5-day-old moths. Heptanal, Z6-nonenal, and benzaldehyde might be very important floral volatiles for host searching and recognized by several olfactory genes with high expression. Some plant volatiles might be important to male moths because the EAG response to 16 plant volatiles and the expression of 43 olfactory genes were significantly larger in males than in females.ConclusionsThe findings of the present study show the effect of adult age on olfactory responses and expression profile of olfactory genes in the migratory pest M. separate.

Response of egg-pupal parasitoid Fopius arisanus (Sonan) to infochemicals from the host eggs' surface of Bactrocera dorsalis (Hendel)

To determine host-related infochemicals that facilitate contact between the egg-pupal parasitoid, Fopius arisanus (Sonan), and its host, Bactrocera dorsalis (Hendel), we analyzed the volatiles on the surface of B. dorsalis eggs by hydrocarbon profiling of the hexane extracts using Gas Chromatography–Mass Spectrometry (GC–MS). These analyses resulted in the identification of 12 components from the egg surface. Among these 6 were alkanes (Dodecane, Heneicosane, Docosane, Tricosane, Tetracosane and Pentacosane) and the proportion was 42.79%, 1 was a fatty acid (Palmitic acid) and the proportion was 3.88%, 3 were fatty acid derivatives (Dodecanoic acid methylester, Lauric acid ethyl ester and Ethyl tetradecanoate) and the proportion was 45.92%, and 2 were alcohols (Tetradecanol and Hexadecanol) and the proportion was 7.41%. 9 chemicals were chosen from the above 12 components to study the EAG and behavioral responses of male and female F. arisanus. The results showed that the EAG and behavioral responses of F. arisanus to same chemical had similar trends, and both EAG relative values and lure rates of females were higher than males' generally. However, for Dodecane and Tetracosane the EAG relative values and lure rates showed extremely significant differences between males and females respectively, for Tricosane there was significant difference, for Ethyl tetradecanoate there was no significant difference between males and females of the relative EAG values but of the lure rates there was significant difference. The results maybe provide new insights from the chemical relationship between parasitoid and host to biocontrol B. dorsalis using F. arisanus.