Responses to sex pheromone and plant odours by olfactory receptor neurons housed in sensilla auricillica of the codling moth, Cydia pomonella (Lepidoptera: Tortricidae)

Morphological characterization and distribution of antennal sensilla of Spodoptera frugiperda (Lepidoptera: Noctuidae) using scanning electron microscopy

The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is a globally significant agricultural pest, causing severe damage to corn production in China. Chemical odor-based trapping is a major approach for FAW control, making it essential to understand the FAW antennal sensillum types to enhance development of effective chemical odor attractants. In this study, we comprehensively examined the antennal sensilla types of FAW, identifying eight types and two subtypes, including Böhm's bristles, sensilla trichoidea, sensilla chaetica (I and II), sensilla coeloconica, sensilla styloconica, sensilla squamiformia (I and II), sensilla auricillica, and sensilla basiconica. Sensilla chaetica II, and sensilla squamiformia II are reported for the first time for FAW in this study. Detailed low-voltage field emission scanning electron microscope (LVSEM) images and descriptions are provided for each sensillum type. This study provides the morphological information to aid in conducting antennal sensillum neurophysiological tests on FAW. RESEARCH HIGHLIGHTS: The types of sensilla of fall armyworm were examined, identifying eight types and two subtypes, including Böhm's bristles, sensilla trichoidea, sensilla chaetica (I and II), sensilla coeloconica, sensilla styloconica, sensilla squamiformia (I and II), sensilla auricillica, and sensilla basiconica. Detailed low-voltage field emission scanning electron microscope images and descriptions were provided for each sensillum type.

Ultrastructural and Descriptive Study on the Adult Body Surface of Heortia vitessoides (Lepidoptera: Crambidae)

Heortia vitessoides Moore, 1885 (Lepidoptera: Crambidae) is an economically important lepidopteran pest that caused severe damage to the plantation area of Aquilaria sinensis (Lour.) Gilg, 1825 (Thymelaeaceae), resulting in extensive defoliation of the trees during an epidemic. In this study, we used scanning electron microscopy (SEM) to analyze the external morphology and ultrastructure of sensilla on various body parts of H. vitessoides. Specifically, seven, four, four, and five types of sensilla were found, respectively, on the antennae, proboscis, labial palps, and legs. We described the types, distributions, and sexual dimorphism of these sensilla on antennae, and found that the number and size of sensilla differed significantly between males and females. This study provides crucial information for future investigations into the function of these sensilla in H. vitessoides.

Functional Characterization of Pheromone Receptors in the Beet Webworm, Loxostege sticticalis (Lepidoptera: Pyralidae)

Lepidopteran insects mainly rely on sex pheromones to complete sexual communications. Pheromone receptors (PRs) are expressed on the olfactory receptor neurons (ORNs) of the sensilla trichodea and play an essential role in sexual communication. Despite extensive investigations into the mechanisms of peripheral recognition of sex pheromones in Lepidoptera, knowledge about these mechanisms in L. sticticalis remains limited. In this study, five candidate LstiPRs were analyzed in a phylogenetic tree with those of other Lepidopteran insects. Electroantennography (EAG) assays showed that the major sex pheromone component E11-14:OAc elicited a stronger antennal response than other compounds in male moths. Moreover, two types of neurons in sensilla trichodea were classified by single sensillum recordings, of which the "a" neuron specifically responded to E11-14:OAc. Five candidate PRs were functionally assayed by the heterologous expression system of Xenopus oocytes, and LstiPR2 responded to the major sex pheromone E11-14:OAc. Our findings suggest that LstiPR2 is a PR sensitive to L. sticticalis's major sex pheromone compound, E11-14:OAc. Furthermore, this study offers valuable insights into the sexual communication behavior of L. sticticalis, forming a foundation for further analysis of the species' central nervous system.

Scanning electron microscopy study of the antennal sensilla of cob borer, Stenachroia elongella (Lepidoptera: Pyralidae)

Stenachroia elongella is an important pest of maize in Meghalaya, India. To understand the roles of sensory organs in the biological behaviors of this insect, we determined the structure and distribution of sensilla found on the antenna of both male and female S. elongella by scanning electron microscope. The antenna of both sexes is a filiform type, and the overall length of the female antenna is significantly longer than the male antenna. In both sexes, seven types and two subtypes of antennal sensilla are identified; sensilla trichodea, sensilla chaetica, sensilla styloconica, sensilla coeloconica, sensilla auricillica (I, II), sensilla squamiformia and Böhm sensilla. No sexual dimorphism on the specific occurrence of sensilla is observed. Probable functions are discussed based on their external morphology. These results would be helpful for further studies on TEM investigations, electrophysiological recordings, and behavioral studies. RESEARCH HIGHLIGHTS: Seven types and two subtypes of antennal sensilla were observed in both male and female Stenachroia elongella. Morphology and distribution of the antennal sensilla were discussed. Sexual dimorphism was observed on the overall length of the antenna where the female antenna is longer than the male antenna. No sexual dimorphism was observed on specific occurrences of antennal sensilla.

Ultrastructure Characteristics and Sexual Dimorphism of Antennal Sensilla in Tirathaba rufivena (Lepidoptera: Pyralidae)

Tirathaba rufivena Walker, a major insect pest of Areca catechu L., has severely threatened areca nut cultivation in Hainan, China. To improve our understanding of the communication mechanism in host plant seeking and mate-finding for T. rufivena, we described and further characterized the external morphology and internal sensilla structures using scanning electron microscopy and transmission electron microscopy in this study. The antennal morphology was similar between males and females, and there was no significant difference in length between the two sexes. In total, nine sensilla types were identified: sensilla trichodea (Str), sensilla chaetica (Sch), sensilla basiconica (Sba), sensilla auricillica (Sau), sensilla coeloconica (Sco), sensilla styloconica (Sst), Böhm sensilla (Bs), uniporous peg sensilla (Ups) and sensilla squamiformia (Ssq). Sexual dimorphism mainly occurs in variation in the length of Sba, Sch, Sco1 and Bs, and the abundance of Sba, Sau1 and Sau2. The Sba had larger size and numbers on female antennae than that on males, suggesting that these sensilla might have important roles in locating host plants. Both Sau1 and Sau2 were significantly more abundant in females and were probably associated with the detection of mates and host plant for oviposition. These data were important for ongoing studies on host plant seeking and mate-finding behavior in T. rufivena and provided a theoretical foundation to further studies of semiochemical control for this pest.

Electroantennographic activity of 21 aliphatic compounds that bind well to a locust odorant-binding protein

Odorants that bind well to odorant-binding proteins (OBPs) often trigger olfactory responses and have important biological significance. The locust Locusta migratoria (Meyen) (Orthoptera: Acrididae) is a serious agricultural pest. Twenty-one saturated aliphatic compounds with carbon-oxygen bonds and straight chains of 10-17 carbon atoms bind well to an L. migratoria OBP. In this study, olfactory activities of these aliphatic compounds on L. migratoria adult males were tested by electroantennography (EAG) and comparatively analyzed. Four alcohols (undecanol, dodecanol, tridecanol, and tetradecanol), two ketones (2-dodecanone and 2-tridecanone), and two esters (ethyl octanoate and ethyl nonanoate) triggered strong EAG responses, and there was no significant difference between them. The results suggest that the eight compounds are more likely to have important biological significance than the other compounds. Moreover, we found that there is not necessarily a positive correlation between the olfactory activity of odorants and their binding ability with OBP. The study contributes to understanding the odorants with biological significance for L. migratoria and the molecular mechanism of the locust's olfaction.

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.

Morphology and distribution of antennal sensilla in adults of Xylotrechus quadripes

Xylotrechus quadripes (Chevrolat) is the serious woodborer pest of arabica coffee (Coffea arabica L.). To further elucidate the behavior mechanism of the insect based on chemical odorant and to advance effective trapping methods, the typology, distribution, and abundance of antennal sensilla were investigated meticulously in both sexes of X. quadripes by scanning electron microscopy. The filiform antennae of both sexes are composed of 11 segments, namely the scape, pedicel, and nine flagellomeres (f1-9). Ten types (14 subtypes) of sensilla were identified morphologically: sensilla chaetica (three subtypes, Ch.1-3), sensilla basiconica (three subtypes, Ba.1-3), Böhm bristles (Bb), sensilla dentiform (De), sensilla trichodea (Tr), sensilla auricillica (Au), sensilla campaniformia (Ca), grooved peg sensilla (Gp), cuticular pores (Cp), and a newly observed sensillum, named sensilla cone (Cone). The sensilla were mainly distributed in flagellomeres, and the types and amounts increased in frequency from scape to the ninth flagellomere. The numbers of sensilla were the highest on the antennal dorsal side, while the lowest on the ventral side. The types of sensilla were the most abundant on the lateral side, and two sensilla basiconica (Ba.1-2) were found exclusively. The average number of Tr, Ba, and Au on the antenna of the males was significantly greater than females, while the Gp and Cp on the antenna of the females were significantly greater than males. Ca was exclusively occurred on the male antennae but was absent in females. This study discusses the putative functions of the antennal sensilla in adults of X. quadripes based on their characteristics in related species' sensilla, and these results provide an important foundation to clarify the ecological adaption, olfactory recognition mechanism, and to develop the chemical ecology control of X. quadripes.

Morphological characterization and distribution of antennal sensilla of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) using scanning electron microscopy

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a serious polyphagous pest of various field and horticultural crops. A complete knowledge on the morphological features of antennal sensory structures is essential for efficient semiochemical-based control methods. The external structure and distribution of antennal sensilla in male and female adults of H. armigera were investigated using scanning electron microscopy. Eight distinct morphological types of sensilla were identified in both sexes: sensilla trichodea, sensilla basiconica, sensilla auricillica, sensilla coeloconica (multiporous), sensilla chaetica (uniporous), sensilla styloconica, sensilla squamiformia, and Böhm sensilla (aporous) in varying numbers and distribution along the length of the antennae. Of these sensilla, the most widespread are sensilla trichodea and sensilla basiconica on the antennae of both sexes. Female antennae have comparatively greater number of sensilla trichodea than male antennae. Among eight types of sensilla, sensilla basiconica, auricillica, styloconica type II, squamiformia, and Böhm sensilla were identified and reported for the first time in H. armigera. Sexual dimorphism in H. armigera was mainly detected as the variations in sensilla shape, numbers, and distribution of each type of sensilla. The sexual difference was observed in the numbers of sensilla coeloconica, chaetica, styloconica, and squamiformia per flagellomere. The possible functions of these sensilla were discussed in view of previously reported lepidopteran insects. The findings provide fundamental information on the morphology and distribution of antennal sensory structures in H. armigera. It would be useful for further detailed studies on physiological and behavioral function of each sensillum type and helpful for formulating related pest control methods.

Sensilla of the antenna and proboscis of Athetis lepigone (Möschler) (Lepidoptera: Noctuidae)

Sensory structures on the antennae and mouthparts of insects are associated with various activities, such as host location, feeding, attracting a mate, and identifying a suitable oviposition site. Athetis lepigone (Möschler) is an important polyphagous Eurasian pest with more than 30 species of host plants. The larvae target bud leaves, prop roots, and tender stems of many agricultural crops, but the feeding habits of the adults remain poorly known. Aiming to understand the feeding behavior of the species, we investigated the fine morphology of its antennae and proboscis using scanning electron microscopy. The antennae of both sexes are filiform, and bear eight types of sensilla: Böhm's bristles, sensilla squamiformia, trichodea, chaetica, basiconica, coeloconica, styloconica, and auricillica. Sensilla trichodea are the most abundant among these sensillum types. The proboscis consists of two elongated, interlocked maxillary galeae that enclose the food canal by dorsal and ventral legulae. The external galeal surface is covered with numerous triangular microtrichia on Zone 1 and abundant blunt microbumps on Zone 2. The surface of the food canal bears closely connected and smooth semicircular ridges, gradually tapering toward the proboscis tip. Three types of sensilla are noticeable on the proboscis: sensilla trichodea, basiconica, and styloconica. We briefly discuss the putative functional significance of the antennal and proboscis sensilla and, based on the specific structural modifications of the proboscis, predict a flower-visiting habit for A. lepigone.

Ultrastructure of Antennal Morphology and Sensilla of Teak Skeletonizer, Eutectona machaeralis Walker (Lepidoptera: Crambidae)

The leaf skeletonizer, Eutectona machaeralis (Walker) (Lepidoptera: Crambidae), is a severe insect pest of teak trees (Tectona grandis L.f.) in China. To provide some basic evidence for future semiochemical-based management strategies of E. machaeralis, the morphology, ultrastructure, and distribution of antennal sensilla of adults were observed under scanning and transmission electron microscopy. The shape and structure of antenna were similar between males and females, both being filiform. However, the antennal length of males was significantly longer than that of females. Eight morphological sensilla types were observed in both sexes: Böhm's bristles, sensilla trichodea, sensilla basiconica, sensilla chaetica, sensilla styloconica, sensilla coeloconica, sensilla auricillica, and sensilla squamiformia. Significant sexual dimorphism of the sensilla dimensions was found, especially in sensillar length. The putative and potential functions of the different sensilla types are discussed based on the fine structures of the cuticular walls and dendrites of the different sensilla types. We expect these results to help lay a solid foundation for future functional research and develop further investigations of E. machaeralis.

Scanning Electron Microscopy Reveals the Antennal Micromorphology of Lamprodila (Palmar) festiva (Coleoptera: Buprestidae), an Invasive Pest of Ornamental Cupressaceae in Western Palaearctic

Simple Summary

The jewel-beetles, Buprestidae, comprise some economically important invasive pest species. The Cypress jewel beetle, Lamprodila (Palmar) festivafestiva (Linnaeus, 1767), is a new invasive pest of ornamental Cupressaceae, which has recently expanded its range from the Mediterranean region northwards to central and eastern Europe, and to the Russian Black Sea coast. In this study, we used scanning electron microscopy to examine the morphology, numbers, distribution and possible functions of antennal sensilla in both sexes of L. festiva. In total, we identified 15 different (sub)types of sensilla, of which two are present only in females. We discuss possible functions of all examined sensilla and compare them with those in other Buprestidae or other insects. Our study should serve as background information for subsequent chemical ecology research focused mainly on the olfactory sensory system of this rapidly spreading invasive pest.

Abstract

The Cypress jewel beetle, Lamprodila (Palmar) festiva festiva (Linnaeus, 1767), is a serious invasive pest of ornamental Cupressaceae, which has recently expanded its range from the Mediterranean region northwards to central and eastern Europe, and to the Russian Black Sea coast. In this study, we conducted a scanning electron microscopy study of the micromorphology of the male and female antennae of L. festiva to examine the morphology, numbers, distribution, and possible functions of antennal sensilla. Most sensilla are located in the sensory fields within the apical depressions on antennomeres IV–XI. We identified four main types of antennal sensilla in L. festiva: sensilla chaetica (seven subtypes, of which two occur only in females), sensilla basiconica (five subtypes), multiporous grooved pegs (two subtypes), and Böhm sensilla. Females have relatively more sensilla chaetica and multiporous grooved pegs, whereas males have more sensilla basiconica. We discuss possible functions of all examined sensilla and compare them with those in other Buprestidae or other insects. Our study should serve as background information for advanced electrophysiological and behavioral experiments to better understand the functions of different sensilla and mechanisms related to semiochemically based pest control strategies.

Odorant receptor phylogeny confirms conserved channels for sex pheromone and host plant signals in tortricid moths

The search for mates and food is mediated by volatile chemicals. Insects sense food odorants and sex pheromones through odorant receptors (ORs) and pheromone receptors (PRs), which are expressed in olfactory sensory neurons. Molecular phylogenetics of ORs, informed by behavioral and functional data, generates sound hypotheses for the identification of semiochemicals driving olfactory behavior. Studying orthologous receptors and their ligands across taxa affords insights into the role of chemical communication in reproductive isolation and phylogenetic divergence. The female sex pheromone of green budworm moth Hedya nubiferana (Lepidoptera, Totricidae) is a blend of two unsaturated acetates, only a blend of both elicits male attraction. Females produce in addition codlemone, which is the sex pheromone of another tortricid, codling moth Cydia pomonella. Codlemone also attracts green budworm moth males. Concomitantly, green budworm and codling moth males are attracted to the host plant volatile pear ester. A congruent behavioral response to the same pheromone and plant volatile in two tortricid species suggests co-occurrence of dedicated olfactory channels. In codling moth, one PR is tuned to both compounds, the sex pheromone codlemone and the plant volatile pear ester. Our phylogenetic analysis finds that green budworm moth expresses an orthologous PR gene. Shared ancestry, and high levels of amino acid identity and sequence similarity, in codling and green budworm moth PRs offer an explanation for parallel attraction of both species to the same compounds. A conserved olfactory channel for a sex pheromone and a host plant volatile substantiates the alliance of social and habitat signals in insect chemical communication. Field attraction assays confirm that in silico investigations of ORs afford powerful predictions for an efficient identification of behavior-modifying semiochemicals, for an improved understanding of the mechanisms of host plant attraction in insect herbivores and for the further development of sustainable insect control.

Botanical Volatiles Selection in Mediating Electrophysiological Responses and Reproductive Behaviors for the Fall Webworm Moth Hyphantria cunea

Host-plant volatiles play vital roles for insects to locate foraging, mating, and oviposition sites in the environment. As one of the devastating invasive forestry pests, Hyphantria cunea causes a great annual loss in China, and understanding its chemical ecology is an important task. The current research was done in terms of chemical analysis, electrophysiology, and behavioral assays on H. cunea to assess its olfactory reception toward host-plant volatiles. A screen of possible common host volatiles was done, targeting on five favored hosts of H. cunea, harvesting six potential bioactive compounds from a total of 78 odorant components. Six types of antennal sensilla were investigated on their distributions on the antennae, and sexual dimorphism was described. H. cunea showed responses to all selected host-related volatiles in electroantennogram tests, and linalyl butyrate elicited the strongest responses. Furthermore, mating rates in adult pairs that are exposed to dibutyl phthalate and phytol have been significantly increased, while oviposition rates and female fecundity were not influenced. The results of the current study provide initial evidence showing that universal host-derived volatile cues are essential for H. cunea moth in terms of mating, which can also provide insights into the development of botanical attractants.

Morphology and distribution of antennal sensilla in a parasitoid fly, Gymnosoma rotundatum (Diptera: Tachinidae)

Morphology of antennal sensilla and their distribution were investigated in male and female adults of the parasitoid fly Gymnosoma rotundatum (Diptera: Tachinidae) using scanning electron microscopy (SEM). The overall length and shape were not different between males and females from each other. Three basic types of sensilla (sensilla basiconica, s. chaetica, and s. coeloconica) were identified from both sexes, but with variations in numbers and distribution along the antennae. The s. basiconica and s. chaetica could be divided further into subtypes; s. basiconica into three subtypes and s. chaetica into two subtypes. All the basiconica subtypes 1, 2, and 3 were multiporous, indicating that their primary function was olfactory. The sensilla basiconica was most abundant on the antennae of both sexes. The abundance of s. basiconica subtype 1 was different, but other subtypes 2 and 3 were similar between males and females. There was no pore on the cuticular surface of the s. chaetica and s. coeloconica, suggesting that they are likely to be a mechanosensory or a thermohygroreceptory function. The abundance of the two sensillum types was similar between males and females. The morphological information obtained in our study provides a basis for future investigations into the sensory physiological function, and associated behaviors, of each type of sensilla in this parasitoid fly.

A chromosome-level genome assembly of Cydia pomonella provides insights into chemical ecology and insecticide resistance

The codling moth Cydia pomonella, a major invasive pest of pome fruit, has spread around the globe in the last half century. We generated a chromosome-level scaffold assembly including the Z chromosome and a portion of the W chromosome. This assembly reveals the duplication of an olfactory receptor gene (OR3), which we demonstrate enhances the ability of C. pomonella to exploit kairomones and pheromones in locating both host plants and mates. Genome-wide association studies contrasting insecticide-resistant and susceptible strains identify hundreds of single nucleotide polymorphisms (SNPs) potentially associated with insecticide resistance, including three SNPs found in the promoter of CYP6B2. RNAi knockdown of CYP6B2 increases C. pomonella sensitivity to two insecticides, deltamethrin and azinphos methyl. The high-quality genome assembly of C. pomonella informs the genetic basis of its invasiveness, suggesting the codling moth has distinctive capabilities and adaptive potential that may explain its worldwide expansion.

The codling moth, Cydia pomonella, is one of the major pests of pome fruit (apples and pears) and walnuts. Here, the authors sequence and analyze its genome, providing insights on olfactory and detoxification processes that may underlie its worldwide expansion.

EAG Responses of Adult Lobesia botrana Males and Females Collected from Vitis vinifera and Daphne Gnidium to Larval Host-Plant Volatiles and Sex Pheromone

We analysed electroantennogram (EAG) responses of male and female adults of the European grapevine moth Lobesia botrana (Denis et Schiffermüller) (Lepidoptera: Tortricidae) collected as larvae from grapevine (Vitis vinifera L.) and flax-leaved daphne (Daphne gnidium L.). The host-plant odorants tested were either V. vinifera-specific [1-octen-3-ol, (E)-β-farnesene, (E)-4,8-dimethyl-1,3,7-nonatriene], D. gnidium-specific (2-ethyl-hexan-1-ol, benzothiazole, linalool-oxide, ethyl benzanoate), or were shared by both host-plants (linalool, methyl salicylate). Sex pheromone compounds were also tested. The male response to the major pheromone component (E7,Z9-12:Ac) was higher than to any other stimuli, whereas the response to the minor pheromone components (E7,Z9-12:OH and Z9-12:Ac) was not different from the response to the plant odorants. The female response to pheromone was lower or not different from that to plant odorants. Methyl salicylate elicited a higher response in females and (E)-β-farnesene elicited a higher response than several other plant odorants in both sexes. Non-significant interactions between host-plant odorant and sex indicated an absence of sex specialization for host-plant volatile detection. The lack of a significant interaction between plant volatiles and larval host-plants suggested that there was no specialization for plant-volatile detection between V. vinifera and D. gnidium individuals.

Antennal Morphology and Localization of a Pheromone-Binding Protein of Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae)

In the sensory system of insects, olfactory sensilla constitute important functional elements for discriminating odors. Therefore, we used light microscopy and scanning electron microscopy to investigate the morphology and distribution of sensilla in the antennae of Lobesia botrana (Denis & Schiffermüller). In addition, we studied the expression of the gene encoding for pheromone-binding protein 1 (LbotPBP1) by in situ hybridization. Lobesia botrana antennae are filiform and are subdivided into three segments: scape, pedicel, and flagellum. The number of flagellum and their overall length were significantly higher and longer in males than in females. Six morphological types of sensilla (trichodea, chaetica, coeloconica, auricillica, basiconica, and styloconica) were identified on the antennae of both sexes. Trichodea sensilla were the most abundant on the antennae of L. botrana, and three subtypes, discerned by their lengths, were observed. However, sensilla trichodea subtype III was only present in male antennae. Moreover, LbotPBP1 expression was restricted to this type of sensilla, thus confirming its olfactory role, specifically under the context of sexual pheromone perception.

Ultrastructure of antennal sensilla of three fruit borers (Lepidoptera: Crambidae or Tortricidae)

Three fruit borers Conogethes punctiferalis (Guenée) (Crambidae), Grapholita molesta Busck (Tortricidae), and Spilonota albicana Motschulsky (Tortricidae) are serious pests of fruit trees. In this study, their antennal morphology, types of sensilla, and distributions were observed by using SEM (Scanning Electron Microscope). Nine types of sensilla were found on the antennae of C. punctiferalis, while eight types of sensilla were presented on each of G. molesta and S. albicana. The sensilla trichodea with two subtypes were the most abundant sensilla among three fruit borers. Two subtypes of sensillum coeloconica (type I with spines and type II without spines) were observed on the antennae of C. punctiferalis and G. molesta. However, sensilla coeloconica (type I) were only found in S. albicana. Although the sensilla campaniformia were only found on the antennae of C. punctiferalis, our observations confirm sensilla campaniformia presence in the moths. In addition, the functions of these sensilla were discussed based on previously reported lepidopteran insects. As a result, our study may provide useful information for advanced electrophysiological and behavioral experiments to better understand the mechanisms related to pests control.

Diversity of olfactory structures: A comparative study of antennal sensilla in Trichoptera and Lepidoptera

The antenna is the main sensory organ of insects, housing different types of sensilla dedicated to detect chemical cues, motion, humidity and temperature. Sensilla are divided into different types based on their wall structure and morphology. Among the olfactory sensilla, there is an enormous variation in the numbers and morphological types present in different insect taxa. The reasons for this variation remain obscure, though there may be a correlation between sensillum morphology and the characteristics of the stimulus that the olfactory sensory neurons inside the sensillum detect. Here, we report the first comparative analysis of the morphology and ultrastructure of sensilla from Rhyacophila nubila (Rhyacophilidae: Trichoptera) and three species of Lepidoptera, Eriocrania semipurpurella (Eriocraniidae), Lampronia capitella (Prodoxidae), and Bicyclus anynana (Nymphalidae), which use different chemical types of pheromones. Our results, together with a thorough literature review, suggest a shift in major types of olfactory sensilla, from a high proportion of sensilla placodea or auricillica in Trichoptera and the most basal moth lineages (including Eriocraniidae), respectively, to sensilla trichodea in the more derived Lepidoptera (including Prodoxidae and the Ditrysia clade), which parallels the change in the types of sex pheromones used.

Sex Pheromone Dosages and Release Point Densities for Mating Disruption of Ostrinia furnacalis (Lepidoptera: Crambidae) in NE China Corn Fields

Mating disruption of Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae) with its sex pheromone has not been commonly used in NE China due to a lack of information about optimal sex pheromone dosages and the density of release points required in the field. During 2014-2016, first, the two active pheromone ingredients were evaluated in the laboratory alone at ca. 2.5-5.0 mg, or in combination at 0.2-6.0 mg, to disrupt male O. furnacalis mating behaviors. Then, mating disruption areas, with radii of <8.0 m, were determined with those same dosages in corn, an orchard, and soybean fields by comparing male captures in sentinel traps in the control plots with those in corresponding disruption treatments. Finally, 6.0 (F30) and 0.2 mg (Fs) dosages were used in fields at 20-640 and 200-6,400 release points/ha. We found that ≧6.0 mg of the binary pheromone mixture, or ca. 5.0 mg of either of the two single components, completely disrupted mating behaviors, and F30 of the binary mixture provided a 200-m2 disruption area, with at least 50% capture reductions. At a density of 60-640 and 600-6,400 points/ha in a corn field, F30 and Fs dosages provided >90% mating disruption, leaf protection, and ear protection. The dispenser densities and inverse male catches in traps tended to follow a noncompetitive mechanism of mating disruption. Since 85% disruption of mating with 200-400 0.02 mg release points/ha was obtained, that level is recommended as the choice in future NE China O. furnacalis IPM programs.

Addition of Pear Ester With Sex Pheromone Enhances Disruption of Mating by Female Codling Moth (Lepidoptera: Tortricidae) in Walnut Orchards Treated with Meso Dispensers

We evaluated the low-density application of 50 dispensers per hectare, in contrast to the traditional >800 dispensers per hectare in apple orchards, to achieve disruption of communication of adult codling moth, Cydia pomonella (L.), in walnuts, Juglans regia (L.), using several methods. These methods included cumulative catches of male moths in traps baited with sex pheromone (Ph) or codlemone, (E,E)-8,10-dodecadien-1-ol, or a combination of codlemone, pear ester (PE), ethyl (E,Z)-2,4-decadienoate, and acetic acid, and by examining the mating status of females. These data were collected from 2011-2014 in nontreated plots and in similar plots treated with Meso dispensers loaded with codlemone (Ph Meso) or codlemone and PE (Ph + PE Meso). Male moth captures in both the Ph and combination lure traps reduced by 88-96% and 72 to 77%, respectively, compared with traps in the nontreated plots. A significantly higher proportion of female moths were nonmated in plots treated with Ph + PE Meso dispensers (33%) than in plots treated with Ph Meso (18-26%), or left nontreated (13%). In addition, significantly fewer multiple-mated females were trapped in the Ph + PE Meso-treated plots (6%) than in either Ph Meso-treated (13-18%) or nontreated plots (23%). These data suggest that the addition of PE can effectively improve Ph-based disruption of C. pomonella in walnut orchards. In addition, these data suggest that the use of low-density hand-applied dispensers can be an effective and lower-cost approach to manage this pest in the large canopy presented by walnut orchards.

Control and Monitoring of Codling Moth (Lepidoptera: Tortricidae) in Walnut Orchards Treated With Novel High-Load, Low-Density "Meso" Dispensers of Sex Pheromone and Pear Ester

Low-density per ha "meso" dispensers loaded with pear ester, ethyl (E,Z)-2,4-decadienoate, kairomone and codlemone, (E,E)-8,10-dodecadien-1-ol, pheromone of codling moth, Cydia pomonella (L)., were evaluated versus meso dispensers loaded with pheromone alone for mating disruption control in walnut orchards receiving no insecticide sprays. Meso dispensers loaded with codlemone alone (Ph meso) were applied at 50 ha-1 and compared with mesos combining codlemone and pear ester (Ph + PE meso) at 25 and 50 ha-1. Various lures containing pear ester (PE), Ph-PE combo, and an experimental codlemone plus (E)-4,8-dimethyl-1,3,7-nonatriene lure were tested alone and with acetic acid (AA) lures for moth capture efficacy. Male moth capture in pheromone traps was significantly reduced by 88% in Ph meso plots and 96% in Ph + PE meso plots versus control plots. Moth capture in Ph-PE combo traps was significantly reduced for both sexes in all meso plots. Harvest damage by both the codling moth and the secondary pest, navel orangeworm, Amyelois transitella (Walker), was significantly lower in all meso treatment plots compared with damage in control plots. Nut injury level with the Ph + PE meso treatment (50 ha-1) was significantly lower than in Ph meso plots for both codling moth and combined pest injury. Regression analysis suggested that nut infestation levels by navel orangeworm were influenced by codling moth levels. In all meso plots, the most effective lures attracting both codling moth sexes were PE & AA or Ph-PE combo & AA. Demonstrated disruption and control efficacy of these pheromone plus PE-meso dispensers applied at low densities supports development of the meso dispenser tactic for practical pest management use in walnut orchards with inherent low planting densities.

Pheromone Autodetection: Evidence and Implications

Olfactory communication research with insects utilizing sex pheromones has focused on the effects of pheromones on signal receivers. Early pheromone detection studies using the silkworm moth, Bombyx mori L., and Saturniids led to the assumption that emitters, especially females, are unable to detect their own pheromone. Pheromone anosmia, i.e., the inability of females to detect their conspecific sex pheromone, was often assumed, and initially little attention was paid to female behaviors that may result from autodetection, i.e., the ability of females to detect their sex pheromone. Detection of conspecific pheromone plumes from nearby females may provide information to improve chances of mating success and progeny survival. Since the first documented example in 1972, numerous occurrences of autodetection have been observed and verified in field and laboratory studies. We summarize here a significant portion of research relating to autodetection. Electrophysiological and behavioral investigations, as well as expression patterns of proteins involved in pheromone autodetection are included. We discuss problems inherent in defining a boundary between sex and aggregation pheromones considering the occurrence of autodetection, and summarize hypothesized selection pressures favoring autodetection. Importance of including autodetection studies in future work is emphasized by complications arising from a lack of knowledge combined with expanding the use of pheromones in agriculture.

Identification of biotransformation enzymes in the antennae of codling moth Cydia pomonella

Biotransformation enzymes are found in insect antennae and play a critical role in degrading xenobiotics and odorants. In Cydia pomonella, we identified 26 biotransformation enzymes. Among these enzymes, twelve carboxylesterases (CXEs), two aldehyde oxidases (AOXs) and six alcohol dehydrogenases (ADs) were predominantly expressed in antennae. Each of the CpomCXEs presents a conserved catalytic triad "Ser-His-Glu", which is the structural characteristic of known insect CXEs. CpomAOXs present two redox centers, a FAD-binding domain and a molybdenum cofactor/substrate-binding domain. The antennal CpomADs are from two protein families, short-chain dehydrogenases/reducetases (SDRs) and medium-chain dehydrogenases/reducetases (MDRs). Putative catalytic active domain and cofactor binding domain were found in these CpomADs. Potential functions of these enzymes were determined by phylogenetic analysis. The results showed that these enzymes share close relationship with odorant degrading enzymes (ODEs) and resistance-associated enzymes of other insect species. Because of commonly observed roles of insect antennal biotransformation enzymes, we suggest antennal biotransformation enzymes presented here are candidate that involved in degradation of odorants and xenobiotics within antennae of C. pomonella.

Olfactory receptor neuron responses of a longhorned beetle, Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae), to pheromone, host, and non-host volatiles

Longhorn wood-boring beetles (Coleoptera: Cerambycidae) use olfactory cues to find mates and hosts for oviposition. Tetropium fuscum (Fabr.) is an invasive longhorned wood-boring beetle originating from Europe that has been established in Nova Scotia, Canada, since at least 1990. This study used single sensillum recordings (SSR) to determine the response of olfactory receptor neurons (ORNs) in the antennal sensilla of male and female T. fuscum to different kinds of olfactory cues, namely host volatiles, non-host volatiles, the aggregation pheromone of T. fuscum (fuscumol), and an aggregation pheromone emitted by other species of longhorn beetles (3-hydroxyhexan-2-one). Each compound had been previously shown to elicit antennal activity in T. fuscum using electroantennography or had been shown to elicit behavioral activity in T. fuscum or other cerambycids. There have been very few SSR studies done on cerambycids, and ours is the first to compare response profiles of pheromone components as well as host and non-host volatiles. Based on SSR studies with other insects, we predicted we would find ORNs that responded to the pheromone alone (pheromone-specialists), as well as ORNs that responded only to host or non-host volatiles, i.e., separation of olfactory cue perception at the ORN level. Also, because male T. fuscum emerge earlier than females and are the pheromone-emitting sex, we predicted that the number of pheromone-sensitive ORNs would be greater in females than males. We found 140 ORNs housed within 97 sensilla that responded to at least one of the 13 compounds. Fuscumol-specific ORNs made up 15% (21/140) of all recordings, but contrary to our prediction, an additional 22 ORNs (16%) responded to fuscumol plus at least one other compound; in total, fuscumol elicited a response from 43/140 (31%) of ORNs with fuscumol-specific ORNs accounting for half of these. Thus, our prediction that pheromone reception would be segregated on specialist ORNs was only partially supported. Our prediction that females would have more ORNs that responded to fuscumol than would males was also not supported, as there was no difference. The stressed-host volatile linalool elicited the most responses of any compound tested, 43% of all recordings.

Interference of plant volatiles on pheromone receptor neurons of male Grapholita molesta (Lepidoptera: Tortricidae)

In moths, sex pheromone components are detected by pheromone-specific olfactory receptor neurons (ph-ORNs) housed in sensilla trichodea in the male antennae. In Grapholita molesta, ph-ORNs are highly sensitive and specific to the individual sex pheromone components, and thus help in the detection and discrimination of the unique conspecific pheromone blend. Plant odors interspersed with a sub-optimal pheromone dose are reported to increase male moth attraction. To determine if the behavioral synergism of pheromone and plant odors starts at the ph-ORN level, single sensillum recordings were performed on Z8-12:Ac and E8-12:Ac ph-ORNs (Z-ORNs and E-ORNs, respectively) stimulated with pheromone-plant volatile mixtures. First, biologically meaningful plant-volatile doses were determined by recording the response of plant-specific ORNs housed in sensilla auricillica and trichodea to several plant odorants. This exploration provided a first glance at plant ORNs in this species. Then, using these plant volatile doses, we found that the spontaneous activity of ph-ORNs was not affected by the stimulation with plant volatiles, but that a binary mixture of sex pheromone and plant odorants resulted in a small (about 15%), dose-independent, but statistically significant, reduction in the spike frequency of Z-ORNs with respect to stimulation with Z8-12:Ac alone. The response of E-ORNs to a combination of E8-12:Ac and plant volatiles was not different from E8-12:Ac alone. We argue that the small inhibition of Z-ORNs caused by physiologically realistic plant volatile doses is probably not fully responsible for the observed behavioral synergism of pheromone and plant odors.

A Binary Host Plant Volatile Lure Combined With Acetic Acid to Monitor Codling Moth (Lepidoptera: Tortricidae)

Field studies were conducted in the United States, Hungary, and New Zealand to evaluate the effectiveness of septa lures loaded with ethyl (E,Z)-2,4-decadienoate (pear ester) and (E)-4,8-dimethyl-1,3,7-nonatriene (nonatriene) alone and in combination with an acetic acid co-lure for both sexes of codling moth, Cydia pomonella (L.). Additional studies were conducted to evaluate these host plant volatiles and acetic acid in combination with the sex pheromone, (E,E)-8,10-dodecadien-1-ol (codlemone). Traps baited with pear ester/nonatriene + acetic acid placed within orchards treated either with codlemone dispensers or left untreated caught significantly more males, females, and total moths than similar traps baited with pear ester + acetic acid in some assays. Similarly, traps baited with codlemone/pear ester/nonatriene + acetic acid caught significantly greater numbers of moths than traps with codlemone/pear ester + acetic acid lures in some assays in orchards treated with combinational dispensers (dispensers loaded with codlemone/pear ester). These data suggest that monitoring of codling moth can be marginally improved in orchards under variable management plans using a binary host plant volatile lure in combination with codlemone and acetic acid. These results are likely to be most significant in orchards treated with combinational dispensers. Significant increases in the catch of female codling moths in traps with the binary host plant volatile blend plus acetic acid should be useful in developing more effective mass trapping strategies.

Fine Structure of Antennal Sensilla of Paysandisia archon and Electrophysiological Responses to Volatile Compounds Associated with Host Palms

Paysandisia archon (Lepidoptera: Castniidae) is a serious pest of palm trees. A comprehensive knowledge of the insect olfactory system is essential for the development of efficient semiochemical-based control methods. The olfactory sensilla are located particularly on the antennae, and these can detect plant volatiles that provide important cues for the insects in the search for their host plants. To date, the fine structure of P. archon antennal sensilla studies and their role in host-plant perception have not been investigated in great detail. Using light microscopy and scanning and transmission electron microscopy, the antennae of both sexes of P. archon are described here in detail, according to the different types, quantities and distributions of the sensilla. Six types of sensilla were identified. The most widespread are sensilla trichoidea, sensilla basiconica and sensilla auricilica, which are associated with olfactory function. These have cuticular shafts characterised by numerous pores, and they are innervated by two or three sensory neurons. Sensilla coeloconica, sensilla chaetica and sensilla ampullacea are associated with olfactory or olfactory-thermoreception, mechano-gustatory, and thermo-hygroreception functions, respectively. Moreover, the role of P. archon antennae in locating of the host palms was evaluated using electroantennograms, to monitor responses to ester and terpene compounds previously identified as volatiles of damaged/fermenting palm tissues. P. archon showed responses to all of the synthetic chemicals tested, with greater responses in the females, providing a significant sex*dose effect. Among the compounds tested, ethyl isobutyrate elicited the strongest antenna responses. The fine structure of the cuticular and cellular components of the P. archon antenna sensory equipment is described for the first time. The results of this study form an important starting point and complement physiological and behavioural studies, to provide valuable information of practical importance for the development of efficient semiochemical-based control methods.

Response profile of pheromone receptor neurons in male Grapholita molesta (Lepidoptera: Tortricidae)

The response profile of olfactory receptor neurons (ORNs) of male Grapholita molesta (Busck) to the three female sex pheromone components [(Z)-8-dodecenyl acetate (Z8-12:Ac), (E)-8-dodecenyl acetate (E8-12:Ac), and (Z)-8-dodecenyl alcohol (Z8-12:OH)] was tested with single sensillum electrophysiology. Sensilla trichodea housed normally one, but sometimes two or three ORNs with distinct action potential amplitudes. One third of the sensilla contacted contained ORNs that were unresponsive to any of the pheromone components tested. The remaining sensilla contained one ORN that responded either to the major pheromone component, Z8-12:Ac ("Z-cells", 63.7% of sensilla), or to its isomer E8-12:Ac ("E-cells", 7.4% of sensilla). 31% of Z- and E-sensilla had 1 or 2 additional cells, but these did not respond to pheromone. None of the 176 sensilla contacted hosted ORNs that responded to Z8-12:OH. The proportion of Z- and E-cells on the antennae (100:11.6, respectively) is similar to the proportion of these compounds in the blend (100:6, respectively). The response of Z-cells was very specific, whereas E-cells also responded to the Z isomer, albeit with lower sensitivity.

Intraspecific Variation in Female Sex Pheromone of the Codling Moth Cydia pomonella

The codling moth, Cydia pomonella L. (Lepidoptera, Tortricidae), is a major pest of apple, pear and walnut orchards worldwide. This pest is often controlled using the biologically friendly control method known as pheromone-based mating disruption. Mating disruption likely exerts selection on the sexual communication system of codling moth, as male and female moths will persist in their attempt to meet and mate. Surprisingly little is known on the intraspecific variation of sexual communication in this species. We started an investigation to determine the level of individual variation in the female sex pheromone composition of this moth and whether variation among different populations might be correlated with use of mating disruption against those populations. By extracting pheromone glands of individual females from a laboratory population in Canada and from populations from apple orchards in Spain and Italy, we found significant between- and within-population variation. Comparing females that had been exposed to mating disruption, or not, revealed a significant difference in sex pheromone composition for two of the minor components. Overall, the intraspecific variation observed shows the potential for a shift in female sexual signal when selection pressure is high, as is the case with continuous use of mating disruption.

Responses to Pheromones in a Complex Odor World: Sensory Processing and Behavior

Insects communicating with pheromones, be it sex- or aggregation pheromones, are confronted with an olfactory environment rich in a diversity of volatile organic compounds of which plants are the main releaser. Certain of these volatiles can represent behaviorally relevant information, such as indications about host- or non-host plants; others will provide essentially a rich odor background out of which the behaviorally relevant information needs to be extracted. In an attempt to disentangle mechanisms of pheromone communication in a rich olfactory environment, which might underlie interactions between intraspecific signals and a background, we will summarize recent literature on pheromone/plant volatile interactions. Starting from molecular mechanisms, describing the peripheral detection and central nervous integration of pheromone-plant volatile mixtures, we will end with behavioral output in response to such mixtures and its plasticity.

Molecular Characterization and In Silico Analysis of the Pheromone-Binding Protein of the European Grapevine Moth Lobesia botrana (Denis & Schiffermüller) (Lepidoptera, Tortricidae)

The European grapevine moth Lobesia botrana (Denis & Schiffermüller) is an economically important insect in Europe. The species invaded vineyards in Chile, Argentina, and California during 2008-2010 causing severe problems. A major component of the sex pheromone, (E,Z)-7,9-dodecadienyl acetate (E7,Z9-12:Ac), is used in a mating disruption technique when grapevine moth populations are low or to monitor pest numbers. It is thought that these sexual pheromones are blends of volatiles that typically are specific to a species and are transported in the insect antenna by pheromone-binding proteins (PBPs) across the sensillar lymph to the olfactory receptors. Currently, an increasing number of Lepidopteran PBPs are being identified and cloned. However, there are no studies of the olfactory system and of proteins involved in the olfactory perception of L. botrana at the molecular level. In the present study, we report, for the first time, the sequence of a PBP from L. botrana (LbotPBP), which was determined using reverse transcription technology. Homology modeling was used to generate the three-dimensional protein structure. The model suggests that PBP consists of six α-helices as follows: Lys2-Met23 (α1), Thr28-Phe36 (α2), Arg46-Leu59 (α3), His70-Asn80 (α4), Glu84-Asn100 (α5), and Cys108-Lys125 (α6), held together by three disulfide bridges, Cys19-Cys54, Cys50-Cys108, and Cys97-Cys117. Docking simulations based on this model suggested that Trp114 is a key residue in the recognition of acetate pheromones, such as E7,Z9-12:Ac. In silico results in this study are consistent with previous findings in which E7,Z9-12:Ac acts as the most active compound in behavioral and electroantennographic assays.

Disruption of Phthorimaea operculella (Lepidoptera: Gelechiidae) oviposition by the application of host plant volatiles

BACKGROUND

Phthorimaea operculella is a key pest of potato. The authors characterised the P. operculella olfactory system, selected the most bioactive host plant volatiles and evaluated their potential application in pest management. The electrophysiological responses of olfactory receptor neurons (ORNs) housed in long sensilla trichodea of P. operculella to plant volatiles and the two main sex pheromone components were evaluated by the single-cell recording (SCR) technique. The four most SCR-active volatiles were tested in a laboratory oviposition bioassay and under storage warehouse conditions.

RESULTS

The sensitivity of sensilla trichodea to short-chained aldehydes and alcohols and the existence of ORNs tuned to pheromones in females were characterised. Male recordings revealed at least two types of ORN, each of which typically responded to one of the two pheromone components. Hexanal, octanal, nonanal and 1-octen-3-ol significantly disrupted the egg-laying behaviour in a dose-dependent manner. Octanal reduced the P. operculella infestation rate when used under storage conditions.

CONCLUSIONS

This work provides new information on the perception of plant volatiles and sex pheromones by P. operculella. Laboratory and warehouse experiments show that the use of hexanal, octanal, nonanal and 1-octen-3-ol as host recognition disruptants and/or oviposition deterrents for P. operculella control appears to be a promising strategy.

Antenna morphology and sensilla ultrastructure of Tetrigus lewisi Candèze (Coleoptera: Elateridae)

We used scanning and transmission electron microscopy to study the typology, morphology, distributions, and ultrastructures of the antennal sensilla of Tetrigus lewisi Candèze, a predatory click beetle that feeds on longhorned beetles, such as, Monochamus alternatus (Coleoptera: Cerambycidae). We observed eight types of sensilla on the antennae, including sensilla chaetica (with three subtypes: ch.1, ch.2, ch.3), sensilla basiconica (subtypes: ba.1, ba.2, ba.3), sensilla trichodea (subtypes: tr.1, tr.2), as well as sensilla auricillica, sensilla coeloconica, sensilla campaniformia, sensilla styloconica and Böhm's bristles. Significant sexual dimorphism was found in the antenna morphology, as well as in the density of type 2 sensilla trichodea and type 1 sensilla basiconica. We observed thick cuticular walls on sensilla chaetica, sensilla trichodea and sensilla campaniformia; clear pore structures on sensilla trichodea, sensilla basiconica and sensilla auricillica; and double walls with spoke-channels on sensilla coeloconica. The chemoreception, mechanoreception and thermo-/hygro-reception functions were deduced from fine structures on the cuticular walls and the dendrites of the different sensilla types. We suggest that all these sensilla have important roles in the host location, mating and predatory behavior of T. lewisi.

Apple volatiles synergize the response of codling moth to pear ester

Codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae), is a major cosmopolitan pest of apple and other pome fruits. Ethyl (E,Z)-2,4-decadienoate (pear ester) has been identified as a host-derived kairomone for female and male codling moths. However, pear ester has not performed similarly in different fruit production areas in terms of the relative magnitude of moth catch, especially the proportion of females caught. Our work was undertaken to identify host volatiles from apples, and to investigate whether these volatiles can be used to enhance the efficacy of host kairomone pear ester for monitoring female and male codling moths. Volatiles from immature apple trees were collected in the field using dynamic headspace sampling during the active period of codling moth flight. Using gas chromatography-electroantennogram detector (GC/EAD) analysis, six compounds elicited responses from antennae of females. These compounds were identified by GC/mass spectrometry (MS) and comparisons to authentic standards as nonanal, (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, (Z,E)-α-farnesene, and (E,E)-α-farnesene. When the EAD-active compounds were tested individually in the field, no codling moths were caught except for a single male with decanal. However, addition of (E)-4,8-dimethyl-1,3,7-nonatriene, methyl salicylate, decanal, or (E,E)-α-farnesene to pear ester in a binary mixture enhanced the efficacy of pear ester for attracting female codling moths compared to pear ester alone. Addition of the 6-component blend to the pear ester resulted in a significant increase in the number of males attracted, and enhanced the females captured compared to pear ester alone; the number of males and females caught was similar to that with the pear ester plus acetic acid combination lure. Our results demonstrate that it is possible to synergize the response of codling moth to host kairomone by using other host volatiles. The new apple-pear ester host kairomone blend should be helpful for monitoring female codling moth, and may provide the basis for further improvement of codling moth kairomone.

Electrophysiological and behavioral responses of oriental fruit moth to the monoterpenoid citral alone and in combination with sex pheromone

The monoterpenoid citral synergized the electroantennogram (EAG) response of male Grapholita molesta (Busck) antennae to its main pheromone compound Z8-12:OAc. The response to a 10-μg pheromone stimulus increased by 32, 45, 54, 71 and 94% with the addition of 0.1, 1, 10, 100 and 1,000 μg of citral, respectively. There was no detectable response to 0.1, 1, or 10 μg of citral; the response to 100 and 1,000 μg of citral was 31 and 79% of the response to 10 μg of Z8-12:OAc. In a flight tunnel, citral affected the mate-seeking behavior of males. There was a 66% reduction in the number of males orientating by flight to a virgin calling female when citral was emitted at 1,000 ng/min ≍1 cm downwind from a female. Pheromone and citral induced sensory adaptation in male antennae, but citral did not synergize the effect of pheromone. The exposure of antennae to 1 ng Z8-12:OAc/m(3) air, 1 ng citral/m3 air, 1 ng Z8-12:OAc + 1 ng citral/m3 air, or to 1 ng Z8-12:OAc + 100 ng citral/m3 air for 15 min resulted in a similar reduction in EAG response of 47-63%. The exposure of males to these same treatments for 15 min had no effect on their ability to orientate to a virgin calling female in a flight tunnel. The potential for using citral to control G. molesta by mating disruption is discussed.

An attempt to increase efficacy of moth mating disruption by co-releasing pheromones with kairomones and to understand possible underlying mechanisms of this technique

Pheromone-based mating disruption is used worldwide for management of the internal fruit feeding codling moth, Cydia pomonella (L.). There has been recent interest in the potential of improving mating disruption of C. pomonella, and potentially other insect species in general, by broadcasting combinations of pheromone and attractive host-plant kairomones. Given that such kairomones are attractive by themselves (often to both sexes), and also enhance male moth response to their pheromone, it is possible that the effects of competitive attraction and potentially other mechanisms of disruption might be increased. Herein, we tested the hypothesis that mating disruption of C. pomonella could be enhanced by co-deploying pheromone with either of two kairomones: (2E, 4Z)-2, 4-decadienoate (pear ester), or (E)-β-farnesene, as compared with various pheromone blend components alone. When deployed individually, each kairomone caused a low level of synthetic lure trap disruption and (E)-β-farnesene also caused disruption of mating as measured by tethering virgin females. However, combined release of either pear ester or (E)-β-farnesene with pheromone within the same dispenser or as a co-deployed dispenser treatment, respectively, did not increase the level of mating disruption as compared with deploying pheromone alone. Disruption efficacy did not decline when reducing the amount of (E,E)-8,10-dodecadien-1-ol (codlemone) in dispensers by fourfold, when combined with pear ester. C. pomonella readily were observed briefly approaching all dispenser types (with and without pheromone) in the field. Exposure of male C. pomonella to pear ester alone in a manner mimicking observed field exposures did not reduce the number of males able to contact a female-mimic pheromone lure in flight tunnel assays. Also, reduction of male moth behavioral response to pheromone was similar after exposure to codlemone alone, and codlemone and pear ester after exposures that mimicked those observed in the field and none of the main treatments tested (pheromone versus pheromone and either kairomone) affected male moth antennal response seconds after exposure as measured by electroantenogram assays. Collectively, our data indicate that disruption of C. pomonella was not improved by co-releasing pheromone with either kairomone tested from point source devices as compared with pheromone alone at the relatively high loading dosages and associated release rates tested.