Hydrolysis of sex pheromone by antennal esterases of the cabbage looper, Trichoplusia ni

Esterases were isolated from chemosensory sensilla on the antennaeof Trichoplusia ni (Hübner). The disc gel electrophoreticpatterns of these esterases from males and females were similar;however, more bands were observed in the antennae than in 8other tissues examined. Most of the esterases detected in the100,000 g supernatant of the antennal preparation could be dissociatedfrom the 100,000 g membrane pellet. Esterases from both maleand female antennae hydrolyzed the sex attractant, (Z)-7-dodecen-l-olacetate, more rapidly than did the legs, fat body or Malpighiantubules. The enzymes primarily responsible for pheromone catabolismwere less sensitive to paraoxon, eserine and p-(hydroxymercuri)benzoatethan those hydrolyzing 1-napthyl acetate. This suggested thata major portion of the observed pheromone-hydrolytic activitywas due to acetylesterases. Measurement of pheromone hyrolysisin sections of disc gels that contained separated antennal orabdominal body wall esterases revealed 2 peaks of activity withboth tissues; however, the rate of pheromone hydrolysis by theabdominal esterases was slower than that of the antennae. Thesignificance of these findings is discussed in relation to thepossibility of antennal esterases having a functional role inthe olfactory process of males of T. ni.     

Olfactory attraction to aggregation pheromone is mediated by disti-flagellum of antennal segments in Riptortus pedestris

Riptortus pedestris (Hemiptera: Alydidae) is a serious pest of soybean and sweet persimmon and uses male produced aggregation pheromone, (E)-2-hexenyl (Z)-3-hexenoate, (E)-2-hexenyl (E)-2-hexenoate, and tetradecyl isobutyrate to facilitate food location and recognition by conspecifics. Using electroantennogram (EAG) and greenhouse bioassay, we determined which antennal segment is involved in the detection of their aggregation pheromone. In the first EAG test using individual antennal segments, significant EAG responses to 1:1:1 mixture of the aggregation pheromone were observed only from the disti-flagellum segments of both male and female antennae at both pheromone doses tested (1 µg and 100 µg). In the following EAG tests using gradually removed antennal segment(s), EAG response was still maintained when the distal half of a disti-flagellum was surgically removed, while EAG response was lost when whole segment of disti-flagellum or other whole segments were gradually removed from intact antenna of both sexes. In greenhouse experiment, removing one or both segment(s) of disti-flagellum from male or female antennae resulted in significant reduction in their attraction to the aggregation pheromone. Together, these findings support that the disti-flagellum of R. pedestris houses olfactory neurons associated with attraction to their aggregation pheromone.     

Antennal responses of Cydia pomonella (L.) exposed to surfaces treated with methoxyfenozide

Electroantennogram (EAG) measurements were recorded from the antennae of male and female codling moth, Cydia pomonella L., to determine whether adult moths exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide experience a decline in their antennal reception and thus olfactory sensitivity. Such a phenomenon would offer a possible mechanism for the previously reported decreased responsiveness from moths treated with methoxyfenozide to pheromone‐ and plant volatile‐based monitoring lures. Mean EAG data revealed that the antennae from methoxyfenozide‐treated male moths appear to be just as sensitive to various doses of synthetic codlemone as the antennae from the control and surfactant‐treated moths, but they appeared to be less sensitive to the pheromone component 12OH (collected from female effluvia) than the control male antennae. Mean male EAG responses to the pheromone components E8,E10‐12Al and codlemone collected from methoxyfenozide‐treated females were significantly less than the responses towards those two pheromone components collected from the control and surfactant‐treated females. Female moth exposure to methoxyfenozide did not negatively impact the sensitivity of female antennae to the plant volatile pear ester, but it did towards the apple volatile butyl hexanoate. Data from this study show that adult C. pomonella exposure to methoxyfenozide‐treated surfaces does appear to negatively impact, in a minor way, the (i) olfactory sensitivity (or detection) of male antennae towards some components of the female sex pheromone, (ii) the female antennal sensitivity towards a key apple volatile and (iii) the attractiveness of female pheromone effluvia.     

Comparison of male antennal morphology and sensilla physiology for sex pheromone olfactory sensing between sibling moth species: Ectropis grisescens and Ectropis obliqua (Geometridae)

Ectropis grisescens and Ectropis obliqua (Lepidoptera: Geometridae) are sibling pest species that co‐occur on tea plants. The sex pheromone components of both species contain (Z,Z,Z)‐3,6,9‐octadecatriene and (Z,Z)‐3,9‐cis‐6,7‐epoxy‐octadecadiene. E. obliqua has (Z,Z)‐3,9‐cis‐6,7‐epoxy‐nonadecadiene as an additional sex pheromone component, which ensures reproductive segregation between the two species. To ascertain the detection mechanism of olfactory organs for sex pheromone components of E. grisescens and E. obliqua, we applied scanning electron microscopy and single sensillum recording to compare antennal morphology and sensillum physiology in the two species. There was no apparent morphological difference between the antennae of the two species. Both species responded similarly to all three sex pheromone components, including, E. obliqua specific component. The distribution patterns of antennal sensilla trichodea differed between the two species. Sex pheromone olfactory sensing in these sibling species appears to be determined by the density of different types of olfactory sensing neurons. Dose‐dependent responses of sensilla trichodea type 1 to (Z,Z)‐3,9‐cis‐6,7‐epoxy‐octadecadiene, the most abundant component, showed an “all or none” pattern and the other two components showed sigmoidal dose‐response curves with a half threshold of 10^?4 (dilution equal to the concentration of 10 μg/μl). These results suggest that the major sex pheromone component functions as an on–off controller while secondary components function as modulators during olfactory transmission to the primary olfactory center.     

Structure of sensilla, olfactory perception, and behaviour of the bedbug, Cimex lectularius, in response to its alarm pheromone

When deprived of the terminal antennal segments, male and female bedbugs failed to respond to their alarm pheromone and to their assembling scent. Trans-oct-2-en-1-al or trans-hex-2-en-1-al, being the major constituents of the former, induce in adults and larvae of Cimex lectularius a typical alarm behaviour resulting in dispersal of assembled bedbugs; the rapidity of escape depends on the aldehyde concentration in the air. The behavioural threshold for adults is about 9×10¹⁴ molecules of trans-oct-2-en-1-al or 6×10¹⁵ molecules of trans-hex-2-en-1-al per ml air.The distal part of the terminal antennal segment of C. lectularius reveals the following sensilla: bristles (type A1), immersed cones (type B1), plates (type B2), grooved pegs (type C), smooth pegs (type D), hairs with even (type E1), and uneven wall thickness (type E2). The number and distribution of these sensilla is relatively constant and similar in both sexes, but differs slightly in neonate larvae. The pegs and hairs of types C, D, E1 and E2 were shown to have porous walls, a prerequisite for olfactory function.Receptor potentials were recorded from olfactory sensilla of types E1 and E2 after stimulation with trans-hex-2-en-1-al and trans-oct-2-en-1-al. The minimal concentration of trans-hex-2-en-1-al evoking a receptor potential is about 2×10¹⁰ molecules per ml air. The above olfactory sensilla were found to respond also to hexan-1-al, but almost no responses to pentan-1-al, butan-1-al, trans-hex-2-ene, and trans-oct-2-ene were observed. A minimum chain length of six carbons atoms and a terminal carbonyl group are molecular prerequisites for optimal odorant activity, while the presence of a Δ²-double bond is not essential for stimulation of the alarm pheromone receptors of the bedbug.     

Antennal sensilla of the click beetle,Melanotus villosus (Geoffroy) (Coleoptera: Elateridae)

The typology, number and placement of antennal sensilla of the click beetle Melanotus villosus (Geoffroy) (Coleoptera: Elateridae) were studied using scanning electron microscopy. On both the males and females the antennae are made up of the scape, pedicel and nine flagellomeres. Two types of basiconic sensilla, three types of trichoid sensilla, one type of styloconic sensilla, one type of chetoid sensilla, dome-shaped sensilla, grooved pegs, and Böhm sensilla all appear on the antennae of the beetles of both sexes, with the exception of trichoid sensilla type II, whose large number (average of 1635 hairs per antenna) was found only in male beetles. Sensilla trichodea type II evidently respond to the sex pheromone produced by the female beetle. Unlike the other two click beetles, studied up till now, Agriotes obscurus and Limonius aeruginosus, the trichoid and basiconic sensilla of M. villosus, whose proven or assumed function is olfactory, are located predominantly on the flagellomeres ventral extensions. It is assumed that the placement of the olfactory sensilla, mainly on the ventral side of M. villosuss antennae, and their more or less even distribution on the flagellomeres, can be seen as morphological adaptation of this species of insect, whose specific behavioural reaction of olfactory searching is flying, both before and after contact with an odour plume.     

Molecular and functional characterization of three odorant binding proteins from the oriental fruit moth Grapholita molesta (Busck) (Lepidoptera: Tortricide)

Odorant binding proteins (OBPs) act in recognizing odor molecules and their most well‐studied functions are transporting odors across the sensillum lymph to olfactory receptor neurons within the insect antennal sensillum. The adults of Grapholita molesta highly depend on olfactory cues in locating host plants and selecting oviposition sites, in which OBPs play an important role in perceiving and recognizing host plant volatiles. Exploring the physiological function of OBPs could facilitate our understanding of their importance in insects’ chemical communication. In this study, three OBP genes were cloned and named GmolOBP4, GmolOBP5, and GmolOBP10. Quantitative real‐time PCR results indicated that GmolOBP4 and GmolOBP10 were predominantly expressed in adult antennae and GmolOBP5 was expressed in multiple tissues, including head, legs, and wings in addition to antennae. The binding affinities of the three recombinant GmolOBPs (rGmolOBPs) with four sex pheromone components and twenty‐nine host plant volatiles were measured using 1‐N‐Phenyl‐naphthylamine as a fluorescence probe. The three rGmolOBPs exhibited specific binding properties to potential ligands, GmolOBP4 and GmolOBP10 bound to minor sex pheromone components, such as (Z)‐8‐dodecenyl alcohol and dodecanol, respectively. rGmolOBP4 showed intermediate binding ability with hexanal, benzyl alcohol, and pear ester, rGmolOBP5 had a weak affinity for benzaldehyde, pear ester and, methyl jasmonate, and rGmolOBP10 showed strong binding capacity toward hexanol, decanol, and α‐ocimene. We speculate that the GmolOBP4 and GmolOBP10 have dual functions in perception and recognition of host plant volatiles and sex pheromone components, while GmolOBP5 may serve other function(s).     

Morphological and ultrastructural characterization of olfactory sensilla in Drosophila suzukii: Scanning and transmission electron microscopy

Drosophila suzukii is a serious horticultural and quarantine pest, damaging various berry crops. Although the active use of olfactory communication in D. suzukii is well-known, their olfactory sensory system has not been comprehensively reported. Therefore, the present study was carried out to understand the morphology, distribution and ultrastructure of olfactory sensilla present in the antennae and maxillary palps of D. suzukii, through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The olfactory sensilla on the antennae of D. suzukii in both sexes could be classified into three major morphological types, basiconic, trichoid and coeloconic sensilla, according to their shapes. The antennal basiconic sensilla were further divided into three subtypes and the antennal trichoid sensilla into two subtypes, respectively, according to the size of individual sensillum. In contrast to the antennal olfactory sensilla showing diverse morphology, basiconic sensilla was the only type of olfactory sensilla in the maxillary palps of D. suzukii. The basiconic sensilla in the maxillary palps could be further classified into three subtypes, based on their size. Our SEM and TEM observations indicated that multiple nanoscale pores are present on the surface of all types of olfactory sensilla in the antennae and maxillary palps, except coeloconic sensilla. The difference in the morphological types and the distribution of olfactory sensilla suggests that their olfactory functions are different between antennae and maxillary palps in D. suzukii. The results of this study provide useful information for further studies to determine the function of olfactory sensilla in D. suzukii and to understand their chemical communication system.     

Distribution of olfactory and some other antennal sensilla in the male click beetle Agriotes obscurus L. (Coleoptera : Elateridae)

The distribution of 5 types of sensilla was statistically analysed on the 4–10th antennal segments of the male click beetle Agriotes obscurus (Coleoptera : Elateridae). The distribution pattern of the trichoid pheromone receptors (T₂ sensilla) and the olfactory basiconic B₁B₂ sensilla on the antennae of male A. obscurus differs significantly from the distribution pattern of the contact chemoreceptors (T₁ sensilla) and probably the non-olfactory B₇ and D sensilla. A significant peculiarity of the distribution of olfactory sensilla is their location on the antennal segments as 2 separate (dorsal and ventral) fields of sensilla. The numbers of T₂ and B₁B₂ sensilla on dorsal fields of sensilla of the 4–10th segments increase towards the apex of the antenna nearly linearly. On ventral fields of sensilla of the 4–10th antennal segments, the number of B₁B₂ sensilla is nearly uniform; the number of T₂ sensilla in the proximal part of the antenna increases towards the apex, but on distal segments of the antenna their number stabilizes. It is characteristic of both the T₂ and to B₁B₂ sensilla that their numbers are slightly greater on anterior than posterior sides of dorsal sensillar fields, and also greater on posterior than anterior sides of ventral sensillar fields of all antennal segments investigated. We assume that the number of olfactory sensilla on the antennae of male beetles coincides with the distribution of strength of olfactory signal on the antennae of beetles orientating in an odour plume. The distribution patterns of T₂ and B₁B₂ sensilla of the male A. obscurus can be related to some behavioural peculiarities of olfactory orientation (walking or flying and vibrating of the antennae).     

Dramatic changes in patterning gene expression during metamorphosis are associated with the formation of a feather-like antenna by the silk moth, Bombyx mori

Many moths use sex pheromones to find their mates in the dark. Their antennae are well developed with lateral branches to receive the pheromone efficiently. However, how these structures have evolved remains elusive, because the mechanism of development of these antennae has not been studied at a molecular level. To elucidate the developmental mechanism of this type of antenna, we observed morphogenesis, cell proliferation, cell death and antennal patterning gene expression in the branched antenna of the silk moth, Bombyx mori. Region-specific cell proliferation and almost ubiquitous apoptosis occur during early pupal stages and appear to shape the lateral branch cooperatively. Antennal patterning genes are expressed in a pattern largely conserved among insects with branchless antennae until the late 5th larval instar but most of them change their expression dramatically to a pattern prefiguring the lateral branch during metamorphosis. These findings imply that although antennal primordium is patterned by conserved mechanisms before metamorphosis, most of the antennal patterning genes are reused to form the lateral branch during metamorphosis. We propose that the acquisition of a new regulatory circuit of antennal patterning genes may have been an important event during evolution of the sensory antenna with lateral branches in the Lepidoptera.     

Unusual pheromone receptor neuron responses in heliothine moth antennae derived from inter-species imaginal disc transplantation

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons housed in sensilla trichodea along the adult antennae arising from transplantation of the antennal imaginal discs between larval male Helicoverpa zea and Heliothis virescens. The olfactory receptor neurons from the majority of type C sensilla sampled on transplanted antennae displayed response characteristics consistent with those of the species that donated the antennae. However, some of the sensilla type C sampled in either transplant type contained olfactory receptor neurons that responded in a manner typical of the recipient species or other neurons that have not previously been found in the type C sensilla of either species. The single-cell data help to explain behavioral results showing that some transplant males do fly upwind to both species' pheromone blends, an outcome not expected based on known antennal sensory phenotypes. Our results suggest that host tissue can influence antennal olfactory receptor neuron development, and further that because of a common phylogenetic ancestry the donor tissue has the genetic capability to produce a variety of sensillar and receptor types.     

Freeze-fracture characteristics of insect gustatory and olfactory sensilla

Summary Freeze-fracture data on antennal olfactory and labellar gustatory sensilla of the blowfly Calliphora vicina were compared with those of vertebrate olfactory organs.Insect antennal and vertebrate olfactory axons have similar diameters and show vesicular expansions; insect labellar axons are on average twice as thick and show no vesicular expansions. Vertebrate olfactory and insect labellar and antennal axons display similar intramembranous particle densities. Antennal axons show particle arrangements, resembling tight-junctions. The few extremely thick axons found in labella and antennae show particle arrangements resembling gap-junctions.In regions, proximal to the pores in the insect sensillar hairs, P-faces of olfactory and gustatory cilia show about 200 particles/m². The most proximal and distal portions of the sensory cilia, necklaces and regions in the vicinity of the hair pores respectively, were only encountered in antennal sensilla. P-faces of the ciliary membranes underneath these pores display 1,000–1,200 particles/ m² in unbranched and branched cilia. These values agree with values found in vertebrate olfactory cilia. It is suggested that these high particle densities are related to entities involved in chemoreceptive activities.Accessory cell micropliae have P-face densities of 2,000–3,000 particles/ m², values similar to those found in vertebrate supportive cell microvilli. The membranes of the accessory cells display septate-junctions in areas where these cells overlap themselves, each other and in places where they adhere to the exoskeleton or the basement membrane.     

Perception of potential sex pheromones and host-associated volatiles in the cotton plant bug,Adelphocoris fasciaticollis (Hemiptera: Miridae): morphology and electrophysiology

Highly developed chemoreception allows insects to detect foods, find mates, and escape natural enemies. We described the structures and distributions of antennal chemosensilla in Adelphocoris fasciaticollis Reuter by scanning electron microscopy and transmission electron microscopy. Seven major types of antennal sensilla were identified in adults of both sexes. Types 1 and 2 are sensilla chaetica and have thick cuticular walls with conspicuous grooves at their surfaces. Types 3 and 4 are multiporous sensilla trichodea with 1–3 dendrites located at the sensillum lymph, indicating a putative olfactory function. Types 5 and 6 are typical sensilla basiconica but share different characteristics in both external morphology and internal ultrastructure, and may be involved in the perception of host-associated odorants. The last sensilla were Böhm bristles. In addition to the morphological characterization, electrophysiological responses of antennal chemosensilla to 51 semiochemicals were investigated based on electroantennogram (EAG) recordings. Results revealed that different chemical stimuli elicited significantly different dose-dependent EAG responses, in which potential sex pheromone components and green leaf volatiles showed relatively higher EAG responses, but neither monoterpenes nor sesquiterpenes can elicit favorable EAG values. The results provided direct morphological and electrophysiological evidence that the adult antennae of A. fasciaticollis could function in searching for mates and host plants.     

Antennal sense organs of the cockroach, Leucophaea maderae

Adult and nymphal antennae of the cockroach, Leucophaea maderae, contain nine or more different morphological types of sense organs. There is no outwardly apparent sexual dimorphism in adult antennae. Nymphs are dificient in gross numbers of sensilla. Sense organs are classified morphologically by their similarity to known types of sensila and are assigned functions on this basis and preliminary electrophysiological data: Sensilla chaetica (A), thick-walled mechanoreceptive hairs in groups on the antennal base; S. chaetica (B), thick-walled setae which are tactile and probably chemoreceptive, occurring in the antennal base and flagellum; S. trichodea (A), thin-walled chemoreceptive hairs of the flagellum; S. trichodea (B), minute hairs on the scape and pedicel; S. basiconica, thin-walled chemoreceptive pegs, and S. coeloconica (?pit-pegs”?) of the flagellum; S. campaniformia and scolopidia, mechanoreceptors in the base and flagellum; plus Johnston's organ and/or connective chrodotonal organs in the pedicel. Calculations based on absolute counts of sensilla and their known innervation yield an estimate of about 3.3 × 10⁴ sensilla and 10⁵ cells per antenna.     

Investigation of the sensory organs on antennae of the horseflies Hybomitra bimaculata and Tabanus bovinus (Diptera: Tabanidae) by scanning electron microscope

Sensory organs on the antennae of the horseflies Hybomitra bimaculata Macq. and Tabanus bovinus Loew are represented by the same morphological types of sensilla. Never differences in the topographical distribution of the sensilla on antennae have been also found, which can be explained by the similarity of ecological and behavioural adaptations of these insects. First and second antennal segments are found to be supplied with tactile hairs and proprioceptors. Other antennal segments bear sensory organs of several morphological types. Short thin olfactory hairs are most numerous among them. They are present on all segments of the antennal flagellum and belong to two morphological types different by the hair length. In the upper parts of the antennal segments from third to seventh several sensilla trichoidea are present, which probably serve as tactile and taste receptors.     

Antennal glands in Psylliodes chrysocephala, and their possible role in reproductive behaviour

Abstract. The antennal morphology of Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), an important pest of oilseed rape ( Brassica napus ), was studied. Two types of tricellular, integumentary glands were found. The common antennal glands are distributed under all sensilla-bearing parts of male and female antennae. The male-specific antennal glands are only located under a glabrous area found on antennomeres 6–10 of male beetles. The common antennal glands are synthetically active in both pre- and post-diapause adults, but the male specific antennal glands are only active in post-diapause (reproductively active) males. During studies of mating behaviour, the antennae of the males were highly active at the beginning and end of copulation, and in response to increased female activity. The male specific antennal glands may secrete a sex pheromone, and the glabrous area on the male antennae could be the release site for such a pheromone.     

Electroantennogram responses of the male moth, Argyrotaenia velutinana to mixtures of sex pheromone components of the female

Electroantennogram (EAG) responses were recorded from male redbanded leafroller moth, Argyrotaenia velutinana, antennae using mixtures of the three female-produced sex pheromone components: cis-11-tetradecenyl acetate, trans-11-tetradecenyl acetate, and dodecyl acetate (12:Ac). Binary mixtures containing 3%, 8%, and 15% trans in cis elicited significantly higher amplitude responses than other isomeric mixtures as well as pure cis and trans alone. The higher responses to such mixtures were less than additive at high dosages and additive at lower dosages. Receptor adaptation studies using the two isomers support a previous single unit study demonstrating the presence of at least two functionally different receptor sites on male A. velutinana antennae; adaptation to an airstream containing one isomer did not eliminate response to the opposite isomer presented concurrently. An airstream containing the third component, 12:Ac, caused a significant slowing of the recovery rate during the entire recovery period of EAG responses to cis but not trans, suggesting that a possible temporal modulation of neuronal response by 12:Ac may be a means of coding for this component by antennal sensory neurons.     

The structure of the antennae of the Florida Queen butterfly, Danaus gilippus berenice (Cramer)

Interest in the structure of the antennae of the Florida Queen butterfly arises from the finding that a pheromone is active in their courtship. Light and electron microscopic techniques were used to study the sensilla on the antennae and three types of sensilla with perforated walls were identified. The most common of these are short, thin-walled pegs which are distributed over most of the antennal surface. Long, curved, thin-walled pegs occur in patches on the inner medial antennal surface. Multiple coeloconic sensilla are present having up to 50 pegs in one sensillum. On the outer 28 flagellar subsegments there are two such sensilla per subsegment. In addition there are on the antennae long, thick-walled hairs which are mechanoreceptors and probably also contact chemoreceptors. Sunken pegs, the function of which is not known, occur on the antennae. Grooved sensilla were found with the electron microscope but could not be identified with the light microscope. There was no indication of sexual dimorphism in sensilla types or numbers on the antennae.     

Structural and functional differences in the antennal olfactory system of worker honey bees of Apis mellifera and Apis cerana

Olfactory cues are important sensory modalities on individual discrimination, perception, and efficient orientation to food sources in most insects. In honey bees, which are well known as eusocial insects, olfactory cues are mainly used to maintain a colony. Although much research has been reported on olfactory systems in honey bee olfaction, little is known about the differences between two major honey bee species, the European honey bee Apis mellifera and the Asian honey bee Apis cerana. In order to understand the differences of olfactory characteristics in the two species, we compared the distribution of sensory hairs on the antennae and antennal olfactory responses, using electron microscopy, electrophysiological recording and molecular expression level of odorant receptors. Our present study demonstrated that the antennae of A. cerana have more olfactory sensilla than A. mellifera, responding more strongly to various floral volatile compounds. At the molecular level, olfactory co-receptor (Orco), which makes heterodimers with other conventional olfactory receptors, is more abundantly expressed in the antenna of A. cerana than of A. mellifera. These findings extend our understanding of the olfactory systems and behavioral responses to various ecological and biological signals in two closely related honey bee species.