Olfactory sensilla on antennae and maxillary palps of Fannia hirticeps (Stein, 1892) (Diptera: Fanniidae)

The Fanniidae is one of four families in the superfamily Muscoidea (Diptera), including some important medical and hygienic flies. There is a paucity of reports on the ultrastructure of olfactory sensilla for the fanniid species. To provide more information on the morphology of the antennal and palpal sensilla of fanniid fly, Fannia hirticeps (Stein, 1892) has been studied using scanning electron microscopy. The first two antennal segments, scape and pedicel, are covered by microtrichiae and several chaetic sensilla. Six distinct morphological types of sensilla are recorded on the antennal funiculus, including one trichoid, two basiconic, two coeloconic sensilla, and one clavate sensilla. The measurement and density of each sensilla type are also provided. The trichoid sensilla tend to be longer and denser toward the apex of antennal funiculus. Basiconic sensilla spread all over the funicular surface. F. hirticeps bears two types of coeloconic sensilla, type 2 coeloconic sensilla distributed on the distal part of the anterior surface, whereas type 1 distributed on the rest of the funiculus. Clavate sensilla are found on the base of antennal funiculus. Only one large sensory pit is located on the posterior surface. Maxillary palps bear one type of basiconic sensilla. These results are compared with eight other muscid flies. Our findings provide a morphological basis for future investigations on olfactory‐mediated behavior of this group. Microsc. Res. Tech. 2012. © 2012 Wiley Periodicals, Inc.     

Antennal sensilla of the pine weevil Pissodes nitidus Roel. (Coleoptera: Curculionidae)

The antennal sensilla of the pine weevil (Pissodes nitidus Roel.) were observed with scanning electron microscopy and transmission electron microscopy (TEM). The weevil antenna consists of a long scape, a pedicel, and a flagellum with 10 segments; the last four flagellum segments are fused, forming the antennal club, which is densely covered by various sensilla. In both sexes, six types of sensilla, sensilla palmate 1‐4, sensilla chaetica, sensilla trichoid, sensilla basiconic 1‐2, sensilla rod‐like 1‐3, sensilla falciform, were identified. Sensilla palmate represent a unique sensillum type in the Pissodes genus, and named here after their palmate shape, also represent the most abundant sensillum type. The TEM analysis of sensilla palmate represents the first such analysis of this sensillum type, and we speculate that the sensilla have an olfactory function. The sensilla trichoid and chaetica were evenly distributed on the three or four hair bands of the club, with much lower numbers than the palmate sensilla. No significant sexual differences in the types, numbers, and distribution of the antennal sensilla were found except for the size. TEM observation indicated that sensilla chaetica and trichoid may function as olfactory sensors. The putative functions of other sensilla type were also discussed with reference to their morphology, distribution, and ultrastructure. Microsc. Res. Tech., 2011. © 2010 Wiley‐Liss, Inc.     

Types and numbers of sensilla on antennae and maxillary palps of small and large houseflies, Musca domestica (Diptera, Muscidae)

Houseflies, Musca domestica, obtained from a high-larval-density culture were significantly (ca. 1.5 times) smaller than those from a low-larval-density culture. The same held true for their antennae and maxillary palps. Structure, number, and distribution of sensilla on antennae and palps of small and large flies were investigated using Scanning electron microscopy and Transmission electron microscopy. In each funiculus three pits were present, two (Type I) consisting of several compartments and one (Type II) of one compartment. Four types of olfactory sensilla were detected: trichoid sensilla on the funiculi, basiconic sensilla on funiculi and palps, grooved sensilla on funiculi and in pits Type I, and clavate sensilla on funiculi and in pits Type II. Type I pits also contained striated sensilla (presumably hygroreceptors). Mechanosensory bristles were present on scapes, pedicels, and palps. Noninnervated microtrichia were found on the palps and all antennal segments. The large houseflies possessed nearly twice as much sensilla as the small flies. So far, we did not observe differences in behavior between small and large flies. We assumed that small flies, being olfactory less equipped than large flies, may be able to compensate for this by, e.g., visual cues or by their olfactory sensilla being more sensitive than those of large flies. To be able to answer these questions careful studies have to be done on the behavioral responses of small and large flies to environmental stimuli. In addition, electrophysiological studies should be performed to reveal whether the responses of individual sensilla of flies reared under different conditions have been changed.     

Antennal sensilla of the ground beetle Platynus dorsalis (Pontoppidan, 1763) (Coleoptera, Carabidae).

The typology, number, and distribution pattern of antennal sensilla of the ground beetle Platynus dorsalis (Pontoppidan) (Coleoptera, Carabidae) were studied using scanning electron microscopy. The 4.3-4.6-mm-long filiform antennae of the beetles consist of the scape, pedicel, and nine flagellomeres. In both sexes, four subtypes of sensilla chaetica, five subtypes of sensilla basiconica, sensilla trichodea, two subtypes of sensilla campaniformia, sensilla auricillica, and sensilla coeloconica were distinguished. The possible function of the sensilla was discussed and three types of sensilla were considered as olfactory, sensilla trichodea and sensilla basiconica types 1 and 2. Olfactory sensilla form two separate, dorsal and ventral, fields of sensilla on the flagellomeres, which seems to be common in ground beetles. The total numbers of olfactory trichoid (approximately 1,000 hairs) and basiconic sensilla type 1 (1,700-1,800 pegs) on the antennae of P. dorsalis are 5-7 times higher than on the antennae of the ground beetle Bembidion lampros, suggesting that nocturnally active P. dorsalis is much more sensitive to odours perceived by these sensilla than B. lampros with diurnal activity and hunting predominantly by sight. No remarkable sexual differences in the types, numbers, and distribution of antennal sensilla were found in P. dorsalis.     

Morphology and Distribution of Antennal Sensilla of the Bean Bug Riptortus pedestris (Hemiptera: Alydidae)

The bean bug, Riptortus pedestris is a major pest of bean pods and some tree fruits in north‐east Asian countries. Scanning electron microscopy was conducted to investigate the morphology and distribution of antennal sensilla of R. pedestris to help in understanding the sensory mechanisms of the bug. Average antennal lengths of male and female R. pedestris were 11.00 mm and 9.84 mm, respectively, consisting of four distinct segments, scape, pedicel, basiflagellum, and distiflagellum. Based on the gross appearance, the antennal sensilla were classified into four major types (trichodea, basiconica, chaetica, and coeloconica), which could be further classified into four trichoid, three basiconic, four chaotic, and two coeloconic subtypes, based on their size, tip shape, presence of socket, and surface structure. Among them, two subtypes of trichoid sensilla, all three subtypes of basiconic sensilla, four subtypes of chaetic sensilla and two subtypes of coeloconic sensilla had numerous pores along the surface, suggesting their olfactory function. Nine subtypes (2 trichoid, 1 basiconic, 4 chaetic, and 2 coeloconic subtypes) showed a distinct socket structure at the base. Among the four antennal segments, the distiflagellum possessed highest number of sensilla. Trichoid sensilla were most abundant, followed by basiconic, chaetic, and coeloconic sensilla. Each subtype of sensilla exhibited distinct distribution profile along the four antennal segments. Two subtypes of trichoid sensilla, one subtype of basiconic sensilla and one subtype of chaetica sensilla were distributed on scape, pedicel, and basiflagellum, whereas distribution of other subtypes of sensilla was confined to basiflagellum and distiflagellum. Microsc. Res. Tech. 79:501–511, 2016. © 2016 Wiley Periodicals, Inc.     

Sensory structures on the antenna of soldier and worker castes of the termite species Odontotermes parvidens (Termitidae: Isoptera: Blattaria)

Odontotermes parvidens is a commonly found important pest species of termite that primarily feed on a range of cellulosic sources. In termites, communication among the nestmates is the basis of all their daily activities and the sensory structures present on the sensory appendages play a crucial role in different social behaviors perceiving and processing various signals of the nestmates and external environments. So, it is essential to understand in detail their sensory structures in order to understand the sensory system of the species O. parvidens. Thus, we have studied the antenna which is one of the primary sensory appendages of both soldier and worker individuals of the species to elucidate various antennal sensory structures and their distribution using scanning electron microscopy. Based on the morphological features of various sensilla, we observed seven types of sensilla as sensilla chaetica (subtypes I, II, III, and IV), sensilla trichodea (subtypes I and II), sensilla trichodea curvata (subtypes I and II), sensilla basiconica, sensilla capitula, Böhm bristles, and sensilla campaniformia (subtypes I and II) along with numerous glandular pores on the antenna of soldier and worker castes. We have also discussed the putative functions of all the sensilla observed based on their external morphology and distributional characteristics on the antenna of soldier and worker castes of the species O. parvidens. Furthermore, the abundance of sensillar types on the antenna of both the castes has also been discussed.     

Antennal sensory structures in Scaphoideus titanus Ball (Hemiptera: Cicadellidae)

Scaphoideus titanus Ball (Hemiptera: Cicadomorpha) is a leafhopper vector of a phytoplasma disease, the Flavescence dorée (FD), belonging to the vine yellows group. A scanning and transmission electron microscope study has been carried out to investigate the antennal sensory structures. The first two segments, the scape and the pedicel, are short, covered by cuticular scales and devoid of sensilla, with exception of some scattered hairs on the pedicel. The flagellum consists of a unique, elongated segment in which numerous subunits can be recognized, being separated by a sort of cuticular crown. The proximal five subunits bear most of the sensilla. We discovered the presence of single- and double-walled coeloconic sensilla, campaniform sensilla, basiconic sensilla, and trichoid sensilla. A scolopidium is located within the proximal region of the flagellum. Ultrastructural investigations suggest that the antennal sensilla could be involved in the perception of air-borne vibrations, temperature, and humidity variations. The most relevant feature is the extreme reduction of the olfactory sensilla, both in terms of number of sensory structures and sensory neurons per sensillum. The strong reduction in antennal olfactory sensilla to which this specie has undergone is discussed as possible consequence of the specificity toward the host plant.     

Sensilla on different organs of female and male Telenomus dendrolimusi Chu (Hymenoptera: Scelionidae)

Telenomus dendrolimusi Chu is a dominant egg parasitoid of Dendrolimus, which is the most serious conifer defoliator in China. However, the host locating mechanism of T. dendrolimusi is unclear. To take better advantage of this kind of parasitoid, it is necessary to clarify the basic knowledge of the organization of the wasp's sensory system. In this study, the external morphologies of the sensilla on the entire female and male T. dendrolimusi body were described using scanning electron microscopy. Antennae shape and sensilla types were sexually dimorphic. Ten segments and nine types of sensilla were found on the female antenna, including basiconic sensillum (BS), chaeticum sensillum (ChS), trichoid sensillum type 1 (TS1), trichoid sensillum type 2 (TS2), trichoid curvata sensillum (TCS), sickle‐shaped sensillum (SSS), multiporous gustatory sensillum (MGS), campaniform sensillum (CS), and styloconica sensillum (STS). The distribution of the sensilla was directional on female antenna. The male antenna consisted of 12 segments, and 1–3 segments were similar to those of the female. Five types of sensilla were found on male antenna, including BS, ChS, TS1, TCS, and STS. The mouthparts, thoracic legs, eyes, mesonotum, and wings were all covered with longitudinally fluted TSs without hole. A tympana structure appeared on the thoracic legs. Special crevice‐shaped structures were found on the abdomens of both T. dendrolimusi sexes. Possible sensilla functions are discussed according to their morphology. These results provide a solid basis for further researches about the parasitic mechanisms of T. dendrolimusi. Microsc. Res. Tech. 78:1010–1018, 2015. © 2015 Wiley Periodicals, Inc.     

Morphology, ultrastructure, and probable functions of the sense organs on the ovipositor stylets of the hymenoptran parasitoid, Venturia canescens (Gravenhorst)

To help understand the mechanism of host discrimination during oviposition of a parasitoid wasp, Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae), the ultrastructure and morphology of the sense organs on the dorsal and ventral stylets of the ovipositor were examined using scanning and transmission electron microscopy. Ovipositor stylets were scanned for sense organs, because only unsheathed ovipositors are used for probing, stabbing, and host discrimination. Five types of sensilla and secretary pores were identified. Based on their pattern of innervation, the surface-dome and pitted-dome sensilla were thought to have a gustatory function and, thus, are the best candidates for host-discrimination. The arrangements of dendrites of type I and type II campaniform sensilla suggested that these acted as pressure- and mechano-receptors, respectively. Coeloconic sensilla might act as thermo-hygroreceptors, whilst secretary pores might provide lubrication during the process of stabbing for oviposition. Surface-dome sensilla were the most numerous type found followed by secretary pores, pitted-dome sensilla, and coeloconic sensilla. Almost all the sensilla and secretary pores were more numerous on the dorsal than on the ventral stylets, and the maximum number of these sensilla and secretary pores occurred on the distal end of the ovipositor stylets and decreased toward the proximal end. The surface-dome sensilla and secretary pores occurred in alternate rows while the pitted-dome sensilla were scattered all over the surface of the ovipositor stylets, especially on the sides of the stylets.     

Scanning electron microscopy of sensilla on the labial and maxillary palps of adult Callidiellum villosulum Fairmaire (Coleoptera: Cerambycidae)

This study used scanning electron microscopy (SEM) to observe the morphology and sensilla of the labial and maxillary palps of adult Callidiellum villosulum Fairmaire between sexes. Combining behavioral activities may provide an effective control target for this pest. In this study, the results showed that there were three segments on the labial palps and four segments on the maxillary palps. The length and width of each segment of the labial and maxillary palps were significantly larger in females than in males. Four types of sensilla were found on the labial and maxillary palps of both sexes of adult C. villosulum: sensilla basiconica (SB I, II, III, and IV), sensilla chaetica (SCh I and II), sensilla placodea (SP), and sensilla campaniformia (SCa). SB IV, SCa, and Sh II were significantly more developed on female labial and maxillary palps than on males', which may be related to their oviposition behavior. By contrast, SB I was more significantly developed on males than on females, which may be related to their mating selection. At the same time, for both sexes, the numbers of Sh I and Sh II on the maxillary palps were significantly higher on labial palps. Maxillary palps could be inferred to potentially play a more important role than the labial palps in the activities of adult C. villosulum. Results will help us further understand the host selection and egg-laying behavior of adult C. villosulum. Such an understanding shall greatly promote the information-based design of pest control methods.     

Recent advances in insect olfaction, specifically regarding the morphology and sensory physiology of antennal sensilla of the female sphinx moth Manduca sexta.

The antennal flagellum of female Manduca sexta bears eight sensillum types: two trichoid, two basiconic, one auriculate, two coeloconic, and one styliform complex sensilla. The first type of trichoid sensillum averages 34 microm in length and is innervated by two sensory cells. The second type averages 26 microm in length and is innervated by either one or three sensory cells. The first type of basiconic sensillum averages 22 microm in length, while the second type averages 15 microm in length. Both types are innervated by three bipolar sensory cells. The auriculate sensillum averages 4 microm in length and is innervated by two bipolar sensory cells. The coeloconic type-A and type-B both average 2 microm in length. The former type is innervated by five bipolar sensory cells, while the latter type, by three bipolar sensory cells. The styliform complex sensillum occurs singly on each annulus and averages 38-40 microm in length. It is formed by several contiguous sensilla. Each unit is innervated by three bipolar sensory cells. A total of 2,216 sensilla were found on a single annulus (annulus 21) of the flagellum. Electrophysiological responses from type-A trichoid sensilla to a large panel of volatile odorants revealed three different subsets of olfactory receptor cells (ORCs). Two subsets responded strongly to only a narrow range of odorants, while the third responded strongly to a broad range of odorants. Anterograde labeling of ORCs from type-A trichoid sensilla revealed that their axons projected mainly to two large female glomeruli of the antennal lobe.     

External morphology of Trichogramma dendrolimi matsumura (hymenoptera: Trichogrammatidae) organ and ultrastructure of the sensilla

In this article, we described the ultrastructure of the sensilla on the antenna, eyes, mouthparts, wings, legs, and external genitalia of female and male Trichogramma dendrolimi using scanning electron microscopy (SEM). The antenna possessed the most sensilla types. We found 13 types of sensilla on female antenna, which were trichoid sensilla (TS) type 1‐4, chaetica sensilla (ChS) type 1‐2, campaniform sensilla (CaS), falcate sensilla, placoid sensilla (PS) type 1‐2, basiconic capitate peg sensilla (BCPS) type 1, coeloconic sensilla (CoS), and styloconic sensilla. Ten types of sensilla were found on the male antenna, some were the same as that on female T. dendrolimi antenna, such as TS types 1 and 3, CaS, PS type 1, BCPS type 1, and CoS, but TS types 5 and 6, ChS type 3, and BCPS 2 were specific to male T. dendrolimi antenna. The leg possesses eight types of sensilla and a kind of tympana structure. Four types of TSs were found on the wings. On the mouthparts, sensilla on the maxillary and labial palps were unique, including two TSs and one ChS. The ovipositor possesses three types of sensilla, and the copulatory organ possesses two types. The eyes had only one kind of TS. Furthermore, external morphology of antenna and external genitalia revealed distinct sexual dimorphisms. According to their morphology, the possible functions of these sensilla were discussed. These results may further our understanding of the sensory mechanisms of T. dendrolimi in response to infochemicals within the environment. Microsc. Res. Tech., 2012. © 2012 Wiley Periodicals, Inc.     

Distribution patterns and morphology of sensilla on the apical segment of the antennae and palpi of Hydradephaga (Coleoptera: adephaga).

The sensilla on the terminal antennomere of selected Hydradephagans (Coleoptera) are modified in several distinct ways as compared to the sensilla on the terminal antennomere of Geadephagans (Coleoptera). There are no long sensilla of any type on antennae of Hydradephagans, the sensilla are either short, peg-like sensilla that may be recessed in the antennal surface or they are multiporous plate-like sensilla. Multiporous plate-like sensilla have not been found on the antennae of Geadephagans. A pit sensillum occurs on the antennae of one family, Gyrinidae, in the Hydradephaga whereas it is found on the antennae of several species from the families of Geadephaga. The sensilla on the terminal antennomere of Hydradephaga are often grouped into sensory fields that could be located on a particular area of the antennomere. Sensory fields are also located on the apices of the maxillary and labial palps and the most unique sensory fields occur in the Noteridae. The maxillary palpal apex of Hydrocanthus oblongus (Noteridae) is bifurcate and a sensory field with several types of sensilla is at the apex of each branch. The terminal labial palpomere is greatly enlarged and has a long, slender sensory field at the apex and a secondary sensory field on a thumb-like projection. The sensilla on the palpal apices are more diverse and complex in form as compared to the sensilla on the palps of Geadephaga. The most complex sensillum has a cuticular collar and a dome that is divided into six or seven triangular sections. The dome may be opened or closed and a peg-like sensillum with a very wide apical pore is situated beneath the dome.     

Sexual dimorphism in antennal morphology and sensilla ultrastructure of Dendrolimus tabulaeformis Tsai et Liu (Lepidoptera: Lasiocampidae)

Insects rely heavily on olfaction to locate habitat, mates, and oviposition sites, while odorant molecules and the antennal olfactory sensory cells of insects are two indispensable components of olfactory response. Our previous work identified the sex pheromones and volatile compounds derived from host plant of Dendrolimus tabulaeformis Tsai et Liu, a serious economic pest of pines in northern China. However, little is known about the olfactory system of D. tabulaeformis, especially in females. To make a better understanding of the D. tabulaeformis olfactory response, we investigated the structure, innervation, numbers, and distribution of sensilla on the antennae of male and female moth, based on scanning and transmission electron microscopy. The pinniform antennae of this moth bear five types of sensilla: trichoid (TS), basiconica (BS), styloconic (StS), and chaetica (ChS) sensilla, and belt‐type structures (BTSs). The BTSs are hollow and are not chemical sensilla. The ChSs occur on the scape. StS contain dendrite sheaths and four dendrites containing microtubules in their cores. The BS contents are continuous with that in the subsegments. The TSs were sexually dimorphic and could be divided into 12 subtypes based on dendrite number and form. TS1‐4 contained two, three, or four dendrites and were similar in both sexes. TS 5‐8 and TS 9‐12 occurred only on male and female antenna, respectively. We discussed the possible functions of these sensilla. Microsc. Res. Tech., 2013. © 2012 Wiley Periodicals, Inc.     

Antennal sensilla of Apanteles cypris Nixon (Hymenoptera: Braconidae), a larval endoparasitoid of Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae)

Apanteles cypris is an endoparasitoid of rice pest Cnaphalocrocis medinalis. To better understand its host location mechanism, we examined the external morphology of antennal sensilla of A. cypris via scanning electron microscopy. The antennae of male and female A. cypris were filiform in shape, which consist of scape, pedicel, and flagellum with 18 antennomeres. Eleven types of sensilla were recorded in both sexes, including two types of chaetica sensilla, trichodea sensilla without pore, basiconica sensilla I with a tip pore, basiconica sensilla II with wall pores, basiconica sensilla III with a mastoid at the tip, coeloconica sensilla with apparent fingerlike projections, campaniform sensilla with a sprout tip pore, clavatea sensilla, smell pore, and placodea sensilla (PLA) with the multiporous cuticular structure. We also compared the morphology, number, and distribution of the sensory receptors between the two sexes. The length and width of the antennae on the males were significantly greater than that of females. In addition, males of A. cypris showed a larger number and a higher density of PLA compared to females. The morphology and structure of these sensilla were compared to that found in other braconid wasps, and their possible functions in host location were discussed. These observations could facilitate future studies on the biology of olfaction in A. cypris.     

Scanning electron microscopy of antennal sensible of Anoplistes halodendri halodendri and Anoplistes halodendri ephippium (Coleoptera: Cerambycidae)

Anoplistes halodendri halodendri (Pallas, 1776) and Anoplistes halodendri ephippium (Stevens and Dalman, 1817) are two subspecies of the longicorn beetle A. halodendri (Coleoptera, Cerambycidae). In the recent years, these subspecies have been spreading rapidly in Hippophae rhamnoides and Hedysarum scoparium shrubberies in the Chinese provinces of Shanxi and Kingie, causing mass mortality of these shrubberies species and consequently leading to great damage to local ecological environment construction as well as high economic, ecological, and societal losses. To control their hazards effectively, here, we study and compare the types, densities, and distribution of antennal sensilla of A. h. halodendri and A. h. ephippium using scanning electron microscopy. Eight sensilla types were observed on the antennae of these two subspecies, including placoid sensilla (Ps), chaetica sensilla (ch) (types I-III), sensilla basiconica (b) (types I and II), sensilla gemmiformium (G), and auricillica sensilla (au). Ps predominated on the antennae of both A. h. halodendri and A. h. ephippium, followed by b and ch, and G and au. There were differences between the subspecies in the distribution and density of the different sensilla types, with ch I being found exclusively on the antennae of A. h. ephippium and b I and au on the antennae of A. h. halodendri only. With the exception of Ps, the densities of ch II, ch III, b II, and G on the antennae of A. h. halodendri were much higher than on the antennae of A. h. ephippium. These results provide sufficient evidence to clarify the receptive mechanisms used by these two subspecies of longicorn beetles and their responses to volatile semiochemicals released by their host plants as well as discuss their differences with respect to host and habitat selection.     

Antennal and mouthpart sensilla of Acanthoscelides obtectus say (Coleoptera: Bruchidae)

Acanthoscelides obtectus, a serious pest with a worldwide distribution, damages stored seeds of Phaseolus sp. To acquire a better understanding of the sensory orientation of bean weevils, their antennal and palpal sensilla were investigated. The antennae and palps possess several types of sensory hairs: blunt‐tipped sensilla chaetica and trichoidea and also sharp‐tipped sensilla trichoidea, these last being the most numerous. Sensilla basiconica are present only on the flagellomeres, but Böhm bristles occur on the basal sclerite and scape of the antennae. The terminal segments of the maxillary and labial palps bear a group of sensilla styloconica with single apical pores. Sensilla coeloconica are located only on the terminal palpal segments. They were unable to detect any distinct morphological differences between males and females. The possible chemosensory, mechanosensory, and thermo‐/hygroreceptive functions of the sensilla are discussed.     

Sensilla on the antennae,legs and ovipositor of Spathius agrili Yang (Hymenoptera: Braconidae), a parasitoid of the emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)

To investigate the host‐finding mechanisms of Spathius agrili Yang, a parasitoid of the emerald ash borer, Agrilus planipennis Fairmaire, a highly concealed insect pest of Fraxinus spp. The morphology and ultrastructure of sensilla on the antennae and legs of both sexes and on the ovipositors and ovipositor sheaths of females were observed using SEM. Results showed that abundant sensilla trichodea (ST) are distributed on the antennae of both females and males, with the sharp trichoid with a socket at the base being the most numerous sensillum. There are 6–7 sensilla placodea on each segment of the flagellum, arranged lengthways in parallel rows. There are very few sensilla styloconica on the female antennae. The tibiae have mostly sensilla chaetica, whereas three types of ST and the relatively plentiful sensilla chaetica are present on the tarsi. Besides ST, a mass of sensilla squamiformia and small short spines are distributed on the pulvilli. Basically there are no sensilla on the female ovipositor, only steering mechanisms for drilling bark and a variety of v‐shaped grooves. However, a large numbers of short sensilla chaetica and microtrichia are found on the internal surface of ovipositor sheath. The outer surface of the ovipositor sheath also has ST. In addition, a clear spring‐like extension structure can be observed on the fore parts of ovipositor sheath. These findings suggest that the main function of sensilla on the antennae is olfaction, while the sensilla on legs and ovipositor sheaths are mechanoreceptors and tactile sensors. Microsc. Res. Tech. 2010. © 2009 Wiley‐Liss, Inc.     

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.