Antennal sensilla of some forensically important flies in families Calliphoridae, Sarcophagidae and Muscidae

Antennal sensilla of some forensically important fly species in the families Calliphoridae (Chrysomya megacephala, Chrysomya rufifacies, Chrysomya nigripes and Lucilia cuprina), Sarcophagidae (Parasarcophaga dux) and Muscidae (Musca domestica) were studied using scanning electron microscopy. Five types of sensilla were observed: trichoid, basiconic, coeloconic, styloconic and sensory pit. Only trichoid sensilla are found on the scape of the antenna, while both trichoid and styloconic sensilla are located on the antennal pedicels of all species studied. Basiconic sensilla are the most numerous of the sensilla found on the antennae of both sexes of all fly species studied and are comprised of two subtypes: large and small basiconic sensilla. Coeloconic sensilla are characterized by short pegs, with either grooved or smooth surfaces, that are sunken into deep depressions. No marked difference was observed in the number, morphological structure or distributional pattern of any of the sensilla among the species studied, with the exception of there being more numerous sensory pits detected in female P. dux compared to the other species. The suggested function of each antennal sensillum was based on comparison with results of other investigations on similar sensilla.     

Scanning electron microscopy studies of antennal sensilla of Pteromalus cerealellae (Hymenoptera: Pteromalidae)

Pteromalus cerealellae (Ashmead) (Hymenoptera: Pteromalidae) is an ectoparasitoid of several insect pests of stored products. In order to provide requisite background information to support our ongoing research on its host location mechanisms, we examined the external morphology of the antennal sensilla of this parasitoid using scanning electron microscopy. Antennae of male and female P. cerealellae are geniculate in shape, approximately 1300mum in length, and consist of 15 antennomeres. Eight morphological sensilla types were recorded in both sexes, including four types of the highly abundant and widely distributed sensilla trichodea (types I, II and IV are aporous while type III is multiporous), basiconic capitate peg sensilla, coeloconic sensilla, chaetica sensilla, and the most conspicuous plate-like placoid sensilla. Detailed examination of sensilla morphological features including pore presence and numbers suggest that the multiporous type III sensilla trichodea and the multiporous placoid sensilla may play a role in olfaction, whereas the uniporous chaetica sensilla may function as contact chemoreceptors. The types I and II sensilla trichodea are presumably mechanosensory, while the type IV sensilla trichodea may function as proprioceptors. The basiconic capitate peg sensilla and coeloconic sensilla probably function in thermo-hygro reception. Although the shape, structure, and size of antennae of males and female were basically similar, major differences were recorded between the sexes in the distribution of some sensilla types. The type II sensilla trichodea and the multiporous placoid sensilla are relatively more abundant in females, whereas males have greater number of the multiporous type III sensilla trichodea than females. These results are discussed in relation to the possible roles of the sensilla types in the host location behavior of P. cerealellae.     

Morphology,distribution and abundance of antennal sensilla in three stink bug species (Hemiptera: Pentatomidae)

The neotropical stink bugs, Euschistus heros, Piezodorus guildinii and Edessa meditabunda, are important pests of soybean and other crops throughout Central America and in South America from Northern Argentina to Brazil. Mate finding and host plant location in these species depend largely on their chemical communication, and semiochemicals are important mediators of these behaviors. In this study scanning electron microscopy was used to examine the external morphology, distribution and abundance of antennal sensilla on males, females and 5th instar nymphs of these species. Nine morphologically different sensilla types were found: trichod sensilla, type 1 and 2 (ST1 and ST2), long and short basiconic sensilla (SB1, SB2, and SB3), slit-tipped and knob-shaped basiconic sensilla, long chaetic sensilla (Sch) and coeloconic sensilla (Sco). Differences were detected in the abundance and arrangement of the sensilla over the antennal segments in individuals of the same species and among the species studied. The Sch, Sco and the slit-tipped and knob-shaped basiconic sensilla accounted for the major difference in sensilla types among the species. The ST1 was the most abundant type and was restricted to the flagellum. The pedicel of E. heros differs from the pedicels of P. guildinii and E. meditabunda mainly by the absence of Sch. There was a sexual dimorphism in ST1, SB1 and SB2, and this may be an indicative of their roles in detection of male-produced sex pheromone and odors derived from the host plants. The SB2 was lacking in the antennal tip of both sexes and 5th instar nymphs, but was abundant on the second flagellar segment of females of the three species. The same types of sensilla were found on 5th instar nymphs, but always in significantly lower numbers. The morphology and putative functions of each sensilla were compared and discussed.     

Antennal sensory receptors of Pteromalus puparum female (Hymenoptera: Pteromalidae), a gregarious pupal endoparasitoid of Pieris rapae

The external morphology of the antennal sensilla of Pteromalus puparum females (Hymenoptera: Pteromalidae) is described using scanning electron microscopy. The antennae of P. puparum females are geniculate in shape, formed from a large, cylindrical scape with a basal radicel fitting into the antennal socket, a shorter, barrel-shaped pedicel and a flagellum composed of 12 subsegments. Eight morphologically distinct types of sensilla were found on the female antennae. These are: nonporous sensilla trichodea types 1 and 2, which are putative mechanosensilla, nonporous sensilla chaetica, which may function as proprioceptors, uniporous sensilla trichodea types 3 and 4, which are presumably contact chemosensilla, basiconic capitate peg sensilla, which probably function in thermo-hygro reception, multiporous sensilla trichodea, and multiporous sensilla placodea which are all presumed to be olfactory sensilla.     

Sensilla of the antenna and palp of Hydrotaea chalcogaster (Diptera: Muscidae)

Hydrotaea chalcogaster is a fly species of medical and forensic importance in many parts of the world. In this study, we investigated the sensilla of the antenna and palp of the adult female fly using scanning electron microscopy. The antennal scape has one type of sensillum, the sharp-tipped sensillum trichodeum; whereas, the antennal pedicel also possessed this type of sensillum in addition to an unidentified type. Three types of sensilla were found on the flagellum: (1) sensilla basiconica, with both large and small sensilla basiconica showing wall pores, (2) sensilla coeloconica, with a smooth surface, and (3) sensory pits, with wall pores of pegs. The arista is located dorso-laterally on the flagellum and has three segments. Short microtrichia are located around the distal end of its second segment and on the proximal half of the third segment. Both large sharp-tipped sensilla chaetica and small sensilla basiconica with wall pores were observed on the palps. Results of this study contribute to our overall understanding of the ultrastructural morphology of sensilla on the antenna and palp of H. chalcogaster.     

Scanning electron microscopy studies of antennal sensilla of bruchid beetles,Callosobruchus chinensis (L.) and Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

The bruchid beetle, Callosobruchus chinensis (L.) and C. maculatus (F.) (Coleoptera: Bruchidae), are important stored-product insects of stored legume seeds. In this study, the external morphologies of the antennal sensilla on the antennae of both female and male adults of these two species were described using scanning electron microscopy. Antennae of both species are made up of the scape, pedicel, and nine segments of flagellomeres. Antennae of female and male C. maculatus and female of C. chinensis are serrate in shape, while those of male C. chinensis are pectinate. Eight morphological sensilla types were recorded in both sexes, including Böhm bristles (BB), two types of sensilla trichoid (ST1, ST2), sensilla chaetica (SC), two types of sensilla basiconic (SB1, SB2), grooved pegs (GP), and sensilla cavity (SCa). The number of ST1 and SB1 of the male were significantly greater than those of the female of C. chinensis, and the number of ST2 and SB1 of the male were significantly more abundant than those of the female of C. maculatus. The possible functions of the above sensilla types are discussed in light of previously published literature.     

Ultrastructure of antennal sensilla of an autoparasitoid Encarsia sophia (Hymenoptera: Aphelinidae)

Encarsia sophia (Hymenoptera: Aphelinidae) is a parasitoid utilized for biological control of Bemisia tabaci, with selection of prey aided by chemoreceptor organs. The morphology and distribution of the antennal sensilla (chemoreceptors) of E. sophia were examined using Transmission electron micrographs. The total antennal length for E. sophia was 429.28 ± 0.95 μm for females and 437.19 ± 8.21 for males, and each antennae was found to consist of seven sensilla of different types. Both sexes possessed sensilla chaetica, sensilla trichodea, basiconic capitate peg sensilla, multiporous grooved-surface placoid sensilla (MG-PS), uniporous rod-like sensilla, nonporous finger-like sensilla, and sensilla coeloconica. Transmission electron micrographs of longitudinal sections of female antennae showed that they were composed of fat body, cuticle, mesoscutello-metanotal muscles, neurons, and glandular tissue, and cross-sections of the basal MG-PS showed sensillar lymph cavities and dendrites. The MG-PSs were imbedded in an electron-dense mass with cuticular invaginations which acted as pores that connected to a central lumen. The possible function of each type of sensilla is discussed.     

Antennal sensilla of the ground beetle Bembidion properans Steph. (Coleoptera, Carabidae)

The arrangement of antennal sensilla was studied in female and male ground beetles Bembidion properans Steph. (Coleoptera, Carabidae) using scanning electron microscopy. The filiform antennae, 1.8-1.9 mm in length, consist of the scape, pedicel and nine flagellomeres. In both sexes, three types of sensilla chaetica, two types of sensilla trichodea, six types of sensilla basiconica, one type of sensilla coeloconica and one type of sensilla campaniformia were distinguished. The possible function of the sensilla is discussed and three types of sensilla are considered olfactory, sensilla trichodea type 2 and sensilla basiconica types 1 and 2. Olfactory sensilla form dorsal and/or ventral sensillar fields on the flagellomeres and occur sparsely or not at all outside these areas. No sexual differences in the types, number and distribution of antennal sensilla were found.     

Antennal sensillae of five stored-product psocids pests (Psocoptera: Liposcelididae)

Psocids are important pests of stored-products. In this study, the external morphology, types, and distribution of antennal sensillae in both male and female adults of five psocid species, Liposcelis bostrychophila, L. entomophila, L. tricolor, L. decolor, and L. paeta (Psocoptera: Liposcelididae) using scanning electron microscopy. The filiform antennae of the liposcelids are made up of the scape, pedicel, and a long flagellum composed of thirteen flagellomeres. Four morphological types of sensillae are recorded in both male and female species, including Böhm bristles, chaetal sensillae, microtrichial sensillae, and basiconic sensillae. The abundance and distribution of four of these sensilla types on the antennae of male and female are not significantly different in the five psocids species studied. In addition, the possible functions of the above sensilla types are discussed in light of previously published literature; mechanoreception (Böhm bristles and microtrichial sensillae) and olfaction (chaetal and basiconic sensillae). Future functional antennal morphology and electrophysiological studies are needed to confirm these proposed functions.     

Ultrastructure of antennal and posterior abdominal sensilla in Chlorophorus caragana females

Chlorophorus caragana Xie & Wang is a destructive wood-boring beetle that damages Caragana spp. bushes and is distributed in desert areas in north-west China. Using scanning electron microscopy and transmission electron microscopy, we observed the morphology and ultrastructure of antennal and posterior abdominal sensilla in C. caragana females, to discuss the putative functions of these sensilla in host location and oviposition behaviors.In total, seven types (24 subtypes) of sensilla were located on the antenna and posterior abdomen. On the antenna, there were Böhm's bristles (BB.); four subtypes of sensilla chaetica (Ch.1–Ch.4) characterized by non-porous surfaces and sensillum-lymph cavities without dendrites; two subtypes of sensilla trichodea (Tr.1 and Tr.2) with a tip pore and dendrites surrounded by dendritic sheaths; dome-shaped sensilla (Dom.) emerging from a deep cavity with one tip pore; four subtypes of sensilla basiconica (Ba.1–Ba.4) and one type of sensilla auricillica (Au.) with a porous cuticular surface and dendrites in the sensillum-lymph cavity; and one type of sensilla styloconica (Sty.) with grooves on the cuticular wall. On the posterior abdomen, there were four subtypes of sensilla chaetica (Ch.5–Ch.8); three subtypes of sensilla trichodea (Tr.3–Tr.5); and three subtypes of sensilla basiconica (Ba.5–Ba.7; Ba.5 had no groove in the cuticular wall, Ba.6 had one tip pore, and Ba.7 was located in a cuticular cavity). The antennal sensilla were believed to be mechanosensitive, chemosensitive, and sensitive to humidity and temperature, and to play roles in mating, host location and oviposition. The abdominal sensilla are believed to be related to oviposition behaviors.     

Sensory Equipment of the Antennal Flagellum of Several Species of Damalinia (Phthiraptera: Trichodectidae)

Sensilla comprising the sensory equipment of the antennal flagellum of eight species of Damalinia were studied using light and scanning electron microscopy. The sensillar complex consists of three pore organs and two sensilla coeloconica in both males and females. No relationship between their relative position in different genera and species has been found. The ‘pit organs' of the sensilla coeloconica have different shapes according to species. In the apex of the male flagellum, teeth are present in the species studied but the number and shapes are different. Adjacent to the teeth is a cluster of sensilla basiconica. At high magnification, no pores were found in the sensilla walls but their more or less blunt tips have small pores. The inner face of the male flagellum can be serrated or non-serrated.     

Antennal sensilla of the decapitating phorid fly, Pseudacteon tricuspis (Diptera: Phoridae)

Pseudacteon tricuspis Borgmeier is a parasitic decapitating phorid fly (Diptera: Phoridae), which has been released in the southern United States in the last decade for biological control of invasive imported fire ants, Solenopsis spp. In a previous study, we demonstrated that P. tricuspis uses fire ant semiochemicals to locate host worker ants. To provide a solid background in support of our research on mechanisms of host location and olfaction in phorid flies, we studied the morphology of the antennal sensilla of both sexes of P. tricuspis using scanning and transmission electron microscopy. Antennae of P. tricuspis show strong sexual dimorphism in structure and shape: the female has a feathered arista which is located distally on the flagellum and has three sub-segments that bear small spinules of microtrichia. The first two antennal segments, scape and pedicel, bear no sensillum, but were densely covered by microtrichia. Three major types of sensilla were found on the flagellum (funicle) of both sexes: sensilla trichodea, sensilla basiconica, and sensilla coeloconica. Two of these, s. trichodea and s. basiconica were differentiated into three (short, medium, and long) and two (blunt-tip and sharp-tip) subtypes, respectively, for a total of six morphologically different sensilla subtypes. Ultrastructural studies revealed multiple wall pores on s. trichodea and s. basiconica, possibly suggesting chemoreceptory functions. The third and least abundant sensilla type, s. coeloconica, had no wall pores and may function as thermo-hygroreceptors. With the exception of the long subtype of s. trichodea which was recorded only on the male antennae, no other marked sexual differences were recorded in the number and distribution of antennal sensilla in P. tricuspis. These results are discussed in relation to the host location behavior of P. tricuspis, and could facilitate future studies on the neurobiology of olfaction in decapitating phorid flies.     

Functional structure of antennal sensilla in the myrmecophilous beetle Paussus favieri (Coleoptera, Carabidae, Paussini)

The evolution of a myrmecophilous lifestyle in beetles is often associated with morphological alterations. In particular, the antennae of all members of the myrmecophilous ground beetle tribe Paussini are greatly modified, with flagellomeres flattened or crassate, frequently reduced in number from 9 to 5 or even 1 single “antennal club”. The enhanced glandular function of the antennal club has been recently described by scanning (SEM) and transmission (TEM) electron microscopy in Paussus favieri Fairmaire, 1851, where the antenna has become a complex glandular organ, supplying rewarding substances to the ants. In the present work, the antennal sensilla of P. favieri are investigated by SEM, TEM and focused ion beam (FIB/SEM) technology. Most sensilla of scape and antennal club are highly modified mechanoreceptors (i.e. multipointed, fringed, branched, brush-like, sickle-shaped), singly or grouped in tufts (“antennal symphilous organs”). These “trichomes”, here assigned to 8 different morphotypes of sensilla chaetica (Ch.1–Ch.8), show a variable number of basal pores (present also at the base of the taste sensilla Ch.9), which spread dense substances of unknown chemical composition on the seta. Although hygro-, thermo- and chemoreceptors are reduced in number as compared with non-myrmecophilous relatives, and mainly relegated to the apex of the antennal club, their diversity is comparable to that of other carabid beetles: two types of sensilla trichodea (Tr.1–Tr.2); three types of basiconica (Ba.1–Ba.3); one type of campaniformia (Ca); one type of coeloconica (Co) and one type of Böhm sensilla (Bo). Contrary to the hypothesis that Paussus species lack a Johston's organ, a non-connective chordotonal organ composed of 9 groups of scolopidia has been found inside the pedicel. A comparison between sensilla of P. favieri and those of other non-myrmecophilous and myrmecophilous ground beetle species is provided.     

Distribution and morphometric studies of flagellar sensilla in Emphorini bees (Hymenoptera, Apoidea)

The tribe Emphorini is a group of pollen-collecting solitary bees with a geographical distribution restricted to the western hemisphere. Most of the Emphorini bees collect Page 10 linepollen from a few specific plant families and display specialized behaviors for constructing their nests. Insect sensilla are the basic structural and functional units of cuticle receptors, serving mainly mechano- and chemo-receptor functions. The external morphology of the antennal sensilla has been well characterized in species of different families of Apoidea, however there is scarce information about this issue in solitary bees of the family Apidae. For a better understanding of the association between the external sensory system and several types of behaviors which emerged along the evolutionary history of bees, it is important to characterize the antennal receptors in several representative species of this tribe. The distribution of the antennal sensilla on the dorsal flagella of 18 taxa was studied in insects of both sexes, using light and scanning electron microscopy. There were six types of sensilla and setae on the antennae, which were identified as sensilla placodea, trichodea, basiconica, coeloconica, coelocapitular and ampullacea. The sensilla trichodea were classified into subtypes, A, B, C-D. Sensilla subtype A were the most abundant sensilla and were distributed over the entire antennae, while sensilla placodea and sensilla trichodea type B, showed a restricted distribution on specific areas of the flagella. We have recognized four patterns of spatial distribution of setae on dorsal flagella. Species having setae on the distal part of the flagellomeres tended to contain a low density of sensilla trichodea type A. Females showed a higher number of sensilla subtypes B and C-D than males; instead sensilla trichodea A were more abundant in males. No significant difference was found in the number of sensilla placodea, ampullacea, coeloconica and coelocapitular. Sensilla basiconica were found only in females. Our results showed that gustative and tactile sensilla were more abundant in female bees, as well as, olfactory receptors predominate in the antennal system of males. The possible coevolution of flagellar sensilla in males and females of solitary bees is discussed in light of previous reports. Patterns of distribution of setae determine the relative abundance of the types of sensilla in the flagellum.     

Flagellar sensilla of Quadraspidiotus perniciosus Comstock (Rhynchota: Diaspididae) male

The flagellar sensory structures of Quadraspidiotus perniciosus Comstock (Rhynchota: Diaspididae) male have been investigated, using scanning and transmission electron microscopy. Five categories of sensilla have been identified: three types of sensilla trichodea, a sensillum coeloconicum and a sensillum basiconicum. The possible function of sensilla is discussed, considering their location, morphology and ultrastructure. No gustatory sensilla have been detected. All the setae (sensilla trichodea) present on the flagellomeres, except for the three 'knobbed' ones that are mechanosensilla, are cuticular components of olfactory structures. These olfactory sensilla are of two distinct types, having fluted or smooth hairs; furthermore, the fluted ones present different typologies for a varied number of dendrites. They are conceivably used for perceiving female sexual pheromone. It might be that each of the different components of the female sexual pheromone is perceived by a specific sensillum. Two types of supposed thermo-hygroreceptors have been found, one sensillum coeloconicum and two sensilla basiconica.     

Antennal morphology and sensilla ultrastructure of the web-spinning sawfly Acantholyda posticalis Matsumura (Hymenoptera: Pamphiliidae)

Acantholyda posticalis (Hymenoptera: Pamphiliidae) is an important pine pest with a world-wide distribution. To clarify the olfactory receptive mechanism of A. posticalis, scanning electron microscopy and transmission electron microscopy were used to examine the morphology, ultrastructure, and distribution of antennal sensilla of adults from two sites in China. The antennae were filiform, and the flagella comprised 32–35 flagellomeres. Six sensillum types were found. Sensilla chaetica were straight setae with sharply pointed tips and without dendrites in the lumen. Sensilla trichodea were characterized by a parallel-grooved wall and one terminal pore and were innervated by four dendrites at the base. Sensilla basiconica I possessed longitudinally grooved surfaces and multiple terminal pores, with five dendrites in the lumen. Sensilla basiconica II not only had a distinct terminal pore but also had numerous tiny wall pores and many dendritic branches within the sensillum lymph. Sensilla coeloconica had deep longitudinal grooves, one terminal pore and six dendrites, while sensilla campaniformia were thick-walled with a terminal opening and sensory nerve bundles in the lumen. Sensilla chaetica and s. trichodea were most abundant and distributed over the entire antennae, while s. basiconica I and II, s. coeloconica, and s. campaniformia were restricted to the ventral flagellar surfaces. Although the shape and structure of antennae were similar in males and females, females had significantly longer antennae than males, and males had significantly more s. basiconica I than females. We compared the morphology and structure of these sensilla to other Hymenoptera and discussed their possible functions.     

Scanning electron microscopy of foreleg tarsal sense organs of the poultry red mite, Dermanyssus gallinae (DeGeer) (Acari:Dermanyssidae)

Scanning electron microscopy (SEM) studies on the poultry red mite, Dermanyssus gallinae (DeGeer), showed that the tip of the foreleg tarsus of both sexes and early instar stages (larvae, protonymph and deutonymph) bears a cluster of 10 blunt peg-type sensillae. Diversity in size, shape and surface features of the wall of these sensillae characterize the sensilla complex (sensory field). Two short setae (1 and 2) with smooth walls lack detectable pores, whereas three medium-sized setae (4, 5 and 8) bear pores in the wall. Four medium or long setae (3, 6, 7 and 9) have longitudinal grooves or ribs in the wall, whilst one seta (10) possesses both pores and grooves in the wall. Based on the morphology, it is suggested that the porous setae could be olfactory receptors, and the grooved setae could be mechanoreceptors.     

The antennal sensilla of adult mayflies: Rhithrogena semicolorata as a case study

The present paper reports on an ultrastructural investigation of the sensilla on the antennal flagellum of the imago (SEM and TEM) and subimago (SEM) of the mayfly Rhithrogena semicolorata. Sensilla coeloconica of two different sizes, named big and small pegs, are distinguishable in both stages. The big pegs are lobe-shaped with a porous cuticle. The small pegs are more or less conical with a smooth cuticle. TEM seriate sections revealed that the big pegs are innervated by three neurons, which enter the peg. The dendrite sheath opens at the entrance to the peg and leaves the dendrites in contact with the outside through pores and pore tubules. This structure is in agreement with that reported for single-walled olfactory receptors. The small pegs may be innervated by two or four neurons. In both cases, two unbranched dendrites enter the peg and are in close association with the peg wall. These show features typical of hygroreceptors. In the small pegs innervated by four neurons, the other two neurons stop short of entering the peg, and one of them branches. This last could constitute the thermoreceptive unit. The function of the fourth neuron is unknown.The presence of olfactory sensilla in adult mayflies, such as Paleoptera, is relevant to the study of evolutionary trends in insect odour perception. Hygro–thermoreceptors are important in such fragile aquatic insects, which need a moist environment for moulting and reproduction.     

External morphology of Chrysomya pinguis (Walker) (Diptera: Calliphoridae) revealed by scanning electron microscopy

The external morphology of the adult female blow fly, Chrysomya pinguis (Walker, 1858), was examined using scanning electron microscopy. Ultrastructure of the compound eye, ocellus, antenna, palpus, spiracles and portions of the thorax was highlighted. A great difference was observed in sculpture patterns of the corneal lens surface of the ommatidia of the compound eye and that of the ocelli, with the former being densely pustulate and the latter extremely sinuous. Several sensilla types were observed in this study including: sensilla chaetica, sensilla trichodea, sensilla basiconica and sensilla coeloconica. Their probable functions are discussed with reference to other literature. Morphological information about C. pinguis that was revealed in this study allows us to know such types of structures in much better detail and may eventually provide a basis for understanding some of the biological behavior of this fly species in the future.