Types Of Antennal Sensilla Research Articles

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, distribution, ultrastructure, and possible function of the external sensilla on antennae and mouthparts of Echinothrips americanus Morgan (Thysanoptera: Thripidae)

Abstract To better understand the semiochemical detection and reception mechanisms that involved in intra- and interspecific communication, host selection and mating behavior of Echinothrips americanus (Thysanoptera: Thripidae), scanning electron microscopy was used to examine the external morphology, distribution and ultrastructure of the sensilla on antennae and mouthparts. According to serial SEM images, seven types of antennal sensilla in total were observed in both sexes. Sensilla on mouthparts were observed concentrating on the maxillary palps, labial palps, and paraglossa, which is consistent with the previous conclusions. Possible function of the external sensilla is also discussed.

Does antennal sensilla pattern of different populations of Triatoma maculata (Hemiptera: Reduviidae) reveal phenotypic variability?

BackgroundIn Brazil, Triatoma maculata is only found in the State of Roraima and is a vector of Trypanosoma cruzi, the etiological agent of Chagas disease. It occurs in wild, peridomestic and domestic habitats, with an urban infestation in Boa Vista, the capital of this Brazilian state. The aim of this study was to assess the morphological variability of the T. maculata antennal phenotype in three populations of Roraima State, using the antennal sensilla pattern analyzed under optical microscopy.MethodsThe number and distribution of four antennal sensilla types (bristles, thin and thick walled trichoidea, and basiconic) of three Brazilian populations of T. maculata from Roraima State were compared. Univariate and multivariate analyses were performed.ResultsThe antenna of T. maculata presented the four types of sensilla. According to the density and distribution of the antennal sensilla characteristics, the multivariate analyses showed that the laboratory population is morphologically structured. Urban specimens showed a pronounced phenotypic variability. The main differences were observed in the pedicel segment, and between males and females.ConclusionsWe determined the antennal phenotype in three Roraima populations of T. maculata. These results support the idea that the patterns of antennal sensilla are sensitive markers for distinct populations in the Triatominae. The infestations of T. maculata in different habitats reinforces the ability of this vector to become adapted to a variety of environments, which, could have eco-epidemiological implications for the T. cruzi transmission that are still not well understood.

Morphological assessment of the sensilla of the antennal flagellum in different castes of the stingless bee Tetragonisca fiebrigi

AbstractThe antennae of the insects have cuticular structures called sensilla that play a pivotal role in the perception of stimuli and in communication. The morphology of antennal sensilla has been characterized in eusocial bees; however, there is little information on bees of the genus Tetragonisca. Using scanning electron microscopy, 11 types of antennal sensilla were identified in Tetragonisca fiebrigi: trichodea (ST, subtypes I‐VI), placodea, basiconica, coeloconica, ampullacea, and campaniformia. The largest diversity of sensilla was observed in females. The STI was the most abundant, followed by the placodea and the STII. The STI and the sensila placodea were more abundant in males than females, while the STII were more abundant in workers. Significant differences were found in the length of the different types of sensilla among the classes of individuals, with these differences being greater for the STI in males and the STV in queen; for the STII, STIII, and STIV in queen and workers; and for sensila placodea in queens, workers, and soldiers. Multivariate analysis (PCA and UPGMA) showed that the soldier subcaste was separated from the other females. This study advanced our understanding of sensilla morphology, including the number and distribution of sensilla across sexes and castes, and the sensory structures of T. fiebrigi. The results presented provide relevant information for elucidating the communication mechanisms of social insects.

The sensilla trichodea-biased EoblPBP1 binds sex pheromones and green leaf volatiles in Ectropis obliqua Prout, a geometrid moth pest that uses Type-II sex pheromones

Pheromone-binding proteins (PBPs) are considered to play critical roles in sex pheromone detection. Lepidopteran moths can be divided into two taxa, those that use Type-I sex pheromones, such as C10–C18 unsaturated aldehydes, alcohols and acetates, and those that use Type-II pheromones, which are C17–C23 polyunsaturated hydrocarbons and their epoxide derivatives. To date, nearly all the characterized PBPs have been reported in moths with Type-I sex pheromones, and the physiological functions of PBPs in moths that use Type-II sex pheromones remains unclear. In the present study we functionally examine EoblPBP1 in Ectropis obliqua Prout, an important geometrid moth pest that uses Type-II sex pheromones. The phylogenetic analysis of the sequence indicated that EoblPBP1 clustered together with ScerPBP1, a geometrid PBP for detecting Type-II sex pheromones. Scanning electron microscopy showed that E. obliqua moths of both sexes mainly had six types of antennal sensilla, including two types of sensilla trichodea, Str-I and Str-II, sensilla basiconica (Sba), sensilla styloconica (Sst), sensilla chaetica (Sch) and sensilla auricillica (Sau). Of these, Str-I was confirmed to be male moth-specific and had five different subtypes. Fluorescence in situ hybridization revealed that EoblPBP1 was primarily expressed at the base of Str-I. A comparative binding assay showed that recombinant EoblPBP1 bound three sex pheromone components of E. obliqua, demonstrating its involvement in the detection of Type-II sex pheromones. Besides, EoblPBP1 also highly bound unsaturated acetates pheromones and the green leaf volatiles. These results indicate that PBP1 is associated with detecting Type-II sex pheromones in E. obliqua but cannot differentiate Type-II sex pheromones from Type-I sex pheromones or green leaf volatiles. Our findings provide a foundation for further study on molecular basis of Type-II sex pheromone recognition in lepidopteran moths.

Between extreme simplification and ideal optimization: antennal sensilla morphology of miniaturized Megaphragma wasps (Hymenoptera: Trichogrammatidae).

One of the major trends in the evolution of parasitoid wasps is miniaturization, which has produced the smallest known insects. Megaphragma spp. (Hymenoptera: Trichogrammatidae) are smaller than some unicellular organisms, with an adult body length of the smallest only 170 µm. Their parasitoid lifestyle depends on retention of a high level of sensory reception comparable to that in parasitoid wasps that may have antennae hundreds of times larger. Antennal sensilla of males and females of Megaphragma amalphitanum and M. caribea and females of the parthenogenetic M. mymaripenne are described, including sensillum size, external morphology, and distribution. Eight different morphological types of sensilla were discovered, two of them appearing exclusively on female antennae. Two of the types, sensilla styloconica and aporous placoid sensilla, have not been described previously. Regression analyses were performed to detect and evaluate possible miniaturization trends by comparing available data for species of larger parasitoid wasps. The number of antennal sensilla was found to decrease with the body size; M. amalphitanum males have only 39 sensilla per antenna. The number of antennal sensilla types and sizes of the sensilla, however, show little to no correlation with the body size. Our findings on the effects of miniaturization on the antennal sensilla of Megaphragma provide material for discussion on the limits to the reduction of insect antenna.

The structure and morphologic changes of antennae of Cyrtorhinus lividipennis (Hemiptera: Miridae: Orthotylinae) in different instars.

Cyrtorhinus lividipennis Reuter (Hemiptera: Miridae: Orthotylinae), including nymphs and adults, are one of the dominant predators and have a significant role in the biological control of leafhoppers and planthoppers in irrigated rice. In this study, we investigated the antennal morphology, structure and sensilla distribution of C. lividipennis in different instars using scanning electron microscopy. The antennae of both five different nymphal stages and adults were filiform in shape, which consisted of the scape, pedicel and flagellum with two flagellomeres. There were significant differences found in the types of antennal sensilla between nymphs and adults. The multiporous placodea sensilla (MPLA), basiconica sensilla II (BAS II), and sensory pits (SP) only occurred on the antennae of adult C. lividipennis of both sexes. Moreover, there was chaetica sensilla III (CHA III) only observed in males. Sixteen types of antennal sensilla were recorded altogether. They were microtrichia sensilla (MIC), three types of trichoidea sensilla (TRI I-III), three types of chaetica sensilla (CHA I-III), three types of basiconica sensilla (BAS I-III), two types of coeloconica sensilla (COE I and COE II), placodea sensilla (PLA), campaniform sensilla (CAM), MPLA, and SP. In the five different nymphal stages of C. lividipennis, the length of their antennae was significantly increased with the increase of the instar, as well as the number of the TRI II and TRI III. Moreover, sexual dimorphism usually occurred not only in the distribution (CHA III and SP) and the number of antennal sensilla (MIC, BAS II, TRI II, TRI III and MPLA), but also in the length of flagellum (F1 and F2). The possible functions of antennal sensilla are discussed. Those observations could contribute to a better understanding of the development of the olfactory system, and facilitate future studies on the antennal functions in C. lividipennis.

Distribution and Ultrastructure of Sensilla onUlomoides dermestoides(Coleoptera: Tenebrionidae) Antennae1

Abstract Ulomoides dermestoides (Chevrolat) (Coleoptera, Tenebrionidae) is a storage pest and an insect of medical importance. Since this insect lives in the dark and does not emit sounds, its sensation of the external environment is based primarily on sensilla, so it could serve as an ideal model for the study of these structures. Scanning electron microscopy was used to identify the types of antennal sensilla of male and female U. dermestoides and to characterize the function of different types of sensilla observed. The bead-like antenna of U. dermestoides is composed of a scape (one segment), a pedicel (one segment), and a flagellum (nine segments). Six types of sensilla were observed on the antennae of both females and males: the sensilla trichoidea (subtypes I, II, and III), sensilla chaetica (subtypes I, II, and III), sensilla basiconica, basiconic mastoid sensillum, sensilla styloconica (subtypes I and II), and the Bohm bristle. The Student's t test was used to compare the distribution of these sen...

Differential morphology of the sensory sensilla of antennae, palpi, foretarsi and ovipositor of adult Tribolium castaneum (Herbst) (Coleoptera:Tenebrionidae)

The red flour beetle, Tribolium castaneum, is an invasive pest of a variety of stored products that is found in most tropical and subtropical countries. To further understanding of the mechanism of insect-host chemical communication, we examined the morphology, distribution and abundance of various sensilla associated with antennae, palpi, foretarsi and ovipositor by scanning electron microscopy. No sexual dimorphism was found between male and female antennae, palpi and foretarsi. In both sexes, four types of antennal sensilla were characterized: two subtypes of trichoid sensilla (st1-2), four subtypes of basiconic sensilla (bs1-4), multiporous grooved peg (mgp) and styloconica sensilla (sst). Overall, the olfactory and gustatory sensilla were clustered mainly on the three antennal club flagellomeres. The sensory field of both maxillary and labial palps was concentrated on the distal segment forming the chemosensory field. Three types of sensilla on both maxillary and labial palps were characterized: trichodea, basiconica, and two subtypes of sensilla styliconica. Maxillary palps carried higher numbers of all types of sensilla than labial palps. Two types of sensilla were characterized on the fore tarsi: trichoidea and cheatica. Only one type of sensilla was found on the ovipositor, trichodea. The functional roles of these sensilla are discussed in relation to their external structure and distribution. Further anatomical, physiological and behavioral studies on identifying the functional types of these sensilla and their role in the selection of an appropriate food source can provide a basis for the development of semiochemically based control strategies.

The antennae of damselfly larvae

The larval antennal sensilla of two Zygoptera species, Calopteryx haemorroidalis (Calopterygidae) and Ischnura elegans (Coenagrionidae) are investigated with SEM and TEM. These two species have different antennae (geniculate, setaceous) and live in different environments (lotic, lentic waters). Notwithstanding this, similarities in the kind and distribution of sensilla are outlined: in both species the majority of sensilla types is located on the apical portion of the antenna, namely a composed coeloconic sensillum (possible chemoreceptor), two other coeloconic sensilla (possible thermo-hygroreceptors) and an apical seta (direct contact mechanoreceptor). Other mechanoreceptors, such as filiform hairs sensitive to movements of the surrounding medium or bristles positioned to sense the movements of the flagellar segments, are present on the antenna. Similarities in the antennal sensilla types and distribution are observed also with other dragonfly species, such as Onychogomphus forcipatus and Libellula depressa. A peculiar structure with an internal organization similar to that of a gland is observed in the apical antenna of C. haemorroidalis and I. elegans and it is present also in O. forcipatus and L. depressa. The possible function of this structure is at the moment unknown but deserves further investigations owing to its widespread presence in Odonata larvae.

Morphology of Male and Female Antennal Sensilla of Ibalia leucospoides ensiger (Hymenoptera: Ibaliidae)

Since the early 1900s, the Eurasian woodwasp (Sirex noctilio F.; Hymenoptera: Siricidae), a pest of pine (Pinus spp.; Pinales: Pinaceae) trees, has been introduced to various regions in Southern Hemisphere and North America. Among the most effective biocontrol agents of S. noctilio are hymenopteran parasitoids that parasitize various life-stages of woodwasps. Little is known about how these parasitoids locate their host in the wood, but presumably do so through chemolocation using antennae. We examined the external antennal morphology of Ibalia leucospoides ensiger (Norton) (Hymenoptera: Ibaliidae), a major parasitoid of native siricids in North America. Males were found to have two more antennal flagellomeres (13) than females (11), although the total antennal length was similar. The first flagellomere of the male has a distinctive excavated region. Using scanning electron microscopy, we identified seven types of antennal sensilla on male and female I. l. ensiger including campaniform, chaetica (types 1 and 3), coeloconic, fluted basiconica (FB), pits (PI), and placodea. There were no differences in the total number of antennal sensilla between male or female I. l. ensiger. However, females had greater numbers of chaetica type 1 and FB, whereas males had more sensilla placodea. Sensilla were unevenly distributed along the antennae of both males and females. Chaetica type 1 was the most numerous sensillum followed by FB, placodea, and PI. We present analyses of the morphology of the antennae of each sex of I. l. ensiger, and discuss possible function of each sensilla-type and how they may mediate mate location and oviposition activities.

Distribution patterns and morphology of sensilla on the antennae of Plutella xylostella (L.)—A scanning and transmission electron microscopic study

The antennal morphology, types of antennal sensilla, fine structures and distributions of the sensilla in Plutella xylostella L. (Lepidoptera: Plutellidae) were studied by scanning (SEM) and transmission (TEM) electron microscopy. The antenna, scape, pedicel and flagellum were all longer in males than in females. A total of seventeen types of sensilla were identified on the antennae: trichodea (two subtypes), basiconica, coeloconica (three subtypes), Böhm’s bristles (two subtypes), styloconica (two subtypes), squamiformia, auricillica, furcatea (three subtypes), cupuliform organs and terminal sensory pegs. Their numbers and distributions were studied in both male and female, and we found some of the sensilla exhibited various degrees of sexual dimorphisms. Sensilla trichodea were the most abundant of all sensillum types whereas terminal peg was present only once per antenna. Sensilla trichodea in males were bigger (subtype I) and more abundant than in females, however, sensilla basiconica and squamiformia were significantly smaller and less abundant in males than in females. Sensilla styloconica II was only found in females. Seven common sensillum types were studied with TEM to reveal its fine internal structure providing morphological evidences of their sensory functions. Sensilla trichodea I, basiconica and coeloconica III have porous walls suggesting olfactory functions. Combined with the sexual dimorphism, sensilla trichodea male P. xylostella might be involved in detecting sexual pheromones and sensilla basiconica of female might respond to host plant volatiles. Whereas sensilla coeloconica (subtype I and II) and Böhm’s bristles have nonporous walls suggesting non-olfactory functions. The study presented a thorough inventory of sensilla on the antennae and laid a solid foundation for future functional studies of these sensilla in this important economical pest.

Male antenna morphology and its effect on scramble competition in false garden mantids.

Well-developed antennae are crucial for many insects, but especially for scramble competitors, who race to find their mates using female sex cues. In these systems, the ability of males to locate females quickly is thought to be under strong selection. A rarely tested assumption is that males with more sensory structures are able to locate females faster. In the present study, we used the false garden mantid Pseudomantis albofimbriata to investigate male antennal morphology and its effect on male efficiency in finding a mate. We used scanning electron microscopy to describe the major sensilla types and their arrangement along the length of male antennae. We also conducted field enclosure trials relating male antennal morphology to scramble competition in this system. We identified six different types of antennal sensilla (cheatic, trichoid, basiconic, grooved peg, ceolocapitular and campaniform) on male P. albofimbriata antennae. As expected, males who had more trichoid sensilla located females quicker than did males with fewer sensilla. Results of the current study suggest that antenna morphology plays a significant role in mate location and hence scramble competition in the P. albofimbriata mating system.

Antennal morphology and micro‐sensory architecture of the New Zealand magpie moth, Nyctemera annulata (Lepidoptera: Erebidae): diversity, distribution and dimorphism

AbstractInsects rely on chemical information obtained from their surroundings when locating biologically important resources. Detection of these chemicals is mediated by the antennae, which are endowed with various sensory structures called sensilla. Sensilla type, distribution and density vary among species, between sexes and at different life stages, and may provide important information regarding the ability of individuals to detect and process such external stimuli. The aim of this study was to quantitatively investigate the sensory architecture of larval and adult antennae in the New Zealand magpie moth, Nyctemera annulata (Arctiinae). Using scanning electron microscopy the sensilla were identified and classified into 8 types: trichoid, basiconic, chaetic, auricillic, squamiform, styloconic, coeloconic and Böhm's bristles, with multiple subtypes. Larval antennae were found to possess morphology and sensory structures which are essentially ubiquitous across the Lepidoptera. Sexual dimorphism was apparent in the overall antennal morphology as well as in the distribution, density and morphology of particular types of sensilla in adult N. annulata, which likely represents a divergence in sensory functions based on the different resource cues responded to by males (sex pheromones) and females (host plant odours). This is a rare example of a study which quantifies variation in the numbers and dimensions of all antennal sensilla types for males and females to allow a thorough statistical assessment of sexual dimorphism in antennal sensory architecture.

The sensory arrays of the ant, Temnothorax rugatulus

Individual differences in response thresholds to task-related stimuli may be one mechanism driving task allocation among social insect workers. These differences may arise at various stages in the nervous system. We investigate variability in the peripheral nervous system as a simple mechanism that can introduce inter-individual differences in sensory information. In this study we describe size-dependent variation of the compound eyes and the antennae in the ant Temnothorax rugatulus. Head width in T. rugatulus varies between 0.4 and 0.7 mm (2.6–3.8 mm body length). But despite this limited range of worker sizes we find sensory array variability. We find that the number of ommatidia and of some, but not all, antennal sensilla types vary with head width.The antennal array of T. rugatulus displays the full complement of sensillum types observed in other species of ants, although at much lower quantities than other, larger, studied species. In addition, we describe what we believe to be a new type of sensillum in hymenoptera that occurs on the antennae and on all body segments. T. rugatulus has apposition compound eyes with 45–76 facets per eye, depending on head width, with average lens diameters of 16.5 μm, rhabdom diameters of 5.7 μm and inter-ommatidial angles of 16.8°. The optical system of T. rugatulus ommatidia is severely under focussed, but the absolute sensitivity of the eyes is unusually high.We discuss the functional significance of these findings and the extent to which the variability of sensory arrays may correlate with task allocation.

An effective method for the identification and separation of Anopheles minimus, the primary malaria vector in Thailand, and its sister species Anopheles harrisoni, with a comparison of their mating behaviors

BackgroundSpecies of the Anopheles minimus complex are considered to be the primary vectors of malaria in South and Southeast Asia. Two species of the complex, Anopheles minimus and Anopheles harrisoni, occur in Thailand. They are sympatric and difficult to accurately distinguish based on morphological characters. The aim of this study was to investigate the potential of antennal sensory organs to distinguish these two species. Additionally, we investigated their ability to mate in cages of different sizes, as well as the possible mechanism(s) that evokes stenogamous behavior.MethodsLarge sensilla coeloconica present on the antennae of females of An. minimus and An. harrisoni were counted under a conventional light microscope and various types of antennal sensilla were examined under a scanning electron microscope (SEM). Determinations of mating ability were carried out in 20 and 30 cm3 cages with a density resting surface (DRS) of 7.2. The insemination rate, frequency of clasper (gonocoxopodite) movement of the male genitalia during induced copulation and duration of mating of the two species were compared.ResultsThe mean numbers of large sensilla coeloconica on antennal flagellomeres 1–8 and the mean number of large sensilla coeloconica on each flagellum in An. minimus (26.25) and An. harrisoni (31.98) were significantly different. Females of both species bear five types of antennal sensilla: chaetica, trichodea, basiconica, coeloconica and ampullacea. Marked differences in the structure of the large sensilla coeloconica were observed between the two species. Furthermore, only An. minimus could copulate naturally in the small cages. The frequency of clasper movement in the stenogamous An. minimus was significantly higher than in An. harrisoni, but there was no difference in the duration of mating.ConclusionsTo our knowledge, this study is the first to examine and discover the usefulness of large sensilla coeloconica on the antennae of females and the frequency of clasper movement in males for distinguishing the sibling species An. minimus and An. harrisoni. The discovery provides an effective and relatively inexpensive method for their identification. Additionally, the greater frequency of clasper movement of An. minimus might influence its ability to mate in small spaces.

Ultrastructure of sensilla of antennae and ovipositor of Sitotroga cerealella (Lepidoptera: Gelechiidae), and location of female sex pheromone gland

The Angoumois grain moth, Sitotroga cerealella, is a serious pest of stored grains worldwide. Presently, the best effective control against the moth is to disrupt the sexual communication between sexes. Sexual communication in moths includes two processes in which females produce and release pheromones from the sex pheromone gland and males detect and respond to them with a relatively sophisticated olfactory system in their antennae. To better understand these processes, we studied the ultrastructure of antennal and ovipositor sensilla of S. cerealella and determined the location of the female sex pheromone gland. Seven types of antennal sensilla were identified on both sexes: sensilla trichodea, sensilla chaetica, sensilla coeloconica, sensilla styloconica, sensilla auricillica, sensilla squamiformia and Bӧhm bristles. Of these sensilla, the sensilla trichodea were significantly more abundant on male antennae than on those of females, suggesting that these sensilla may detect the sex pheromones. On the ovipositor, only sensilla chaetica of various lengths were found. The sexual gland was an eversible sac of glandular epithelium that was situated dorsally in the intersegmental membrane between the 8th and 9th abdominal segments. These results will lead to a better understanding of mate finding with sex pheromones for this worldwide pest species.

Sexual difference in antennal sensilla abundance, density and size in Callosobruchus rhodesianus (Coleoptera: Chrysomelidae: Bruchinae)

Sexual difference in antennal sensilla size and per area density has rarely been studied in insects. The bruchine seed beetle Callosobruchus rhodesianus (Pic) (Coleoptera: Chrysomelidae: Bruchinae) is distributed over Central and Southern Africa and is a pest of stored legume seeds, especially cowpeas Vigna unguiculata. Here, we study the type, abundance, morphology and per area density of antennal sensilla on each antennal segment and their sexual differences in C. rhodesianus. The antennae of normal individuals consist of the scape, pedicel and nine flagellomeres as in other congeneric species. Sizes of most antennomeres are larger in males than in females. We observed the following eight different types of antennal sensilla: sensilla trichodea types 1 and 2 (ST1, ST2), sensilla cavitae (SCa), sensilla chaetica (SC), sensilla basiconica types 1, 2 and 3 (SB1, SB2, SB3) and Bohm bristles (BB). The SCa is found on all antennomeres unlike in congeners (C. chinensis and C. maculatus). The ST1, the most numerous and longest antennal sensilla type, is denser and thinner in females than in males but more abundant in males than in females. Since the ST1 is considered to serve as a chemoreceptor, the sexual difference in the ST1 may benefit males in searching for mates.

Olfactory perception and behavioral effects of sex pheromone gland components in Helicoverpa armigera and Helicoverpa assulta.

Two sympatric species Helicoverpa armigera and Helicoverpa assulta use (Z)-11-hexadecenal and (Z)-9-hexadecenal as sex pheromone components in reverse ratio. They also share several other pheromone gland components (PGCs). We present a comparative study on the olfactory coding mechanism and behavioral effects of these additional PGCs in pheromone communication of the two species using single sensillum recording, in situ hybridization, calcium imaging, and wind tunnel. We classify antennal sensilla types A, B and C into A, B1, B2, C1, C2 and C3 based on the response profiles, and identify the glomeruli responsible for antagonist detection in both species. The abundance of these sensilla types when compared with the number of OSNs expressing each of six pheromone receptors suggests that HarmOR13 and HassOR13 are expressed in OSNs housed within A type sensilla, HarmOR14b within B and C type sensilla, while HassOR6 and HassOR16 within some of C type sensilla. We find that for H. armigera, (Z)-11-hexadecenol and (Z)-11-hexadecenyl acetate act as behavioral antagonists. For H. assulta, instead, (Z)-11-hexadecenyl acetate acts as an agonist, while (Z)-9-hexadecenol, (Z)-11-hexadecenol and (Z)-9-hexadecenyl acetate are antagonists. The results provide an overall picture of intra- and interspecific olfactory and behavioral responses to all PGCs in two sister species.

Sexual dimorphism in antennal morphology and sensilla ultrastructure of a pupal endoparasitoid Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae).

Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae), a pupal parasitoid of a great number of Lepidoptera pests, has a great potential for biological control. To investigate the olfactory system of this parasitoid, we examined the morphology and ultrastructure of the antennal sensilla of both male and female T. howardi using scanning and transmission electron microscopic techniques. Antennae of male and female T. howardi were geniculate in shape, which consisted of scape, pedicel and flagellum with 5 and 4 flagellomeres, respectively. The sexual differences were recorded in the types, structure, distribution and abundance of antennal sensilla of T. howardi. Fourteen morphologically distinct types of antennal sensilla were found on the female antennae, while seventeen on the male antennae. They were: multiporous plate sensilla (MPS1-4), chaetica sensilla (CH1-3), multiporous trichodea sensilla (MTS), aporous trichodea sensilla (ATS1-5), multiporous grooved peg sensilla (MGPS), coeloconic sensilla (COS), campaniform sensilla (CAS), terminal finger-like hairy sensilla (TFI), cuticular pore (CP), and ventral sensory plaque (VSP). MPS4, ATS (3-5), and VSP only occurred on the male antennae, while MPS2 and MPS3 only on the female antennae. The MPSs, MTS, MGPS, TFI, and CP may function as olfactory sensilla involving in detecting odor stimuli whereas the ATSs, CHs, and CAS may serve as mechanoreceptors. COS were presumed to play a role as chemo-, thermo- or hygro-receptor. The results could facilitate future studies on the biology of olfaction in T. howardi.