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.     

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.     

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

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

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.     

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.     

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 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.     

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.     

Morphological characterization of the antennal sensilla of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), with reference to their probable functions

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is one of the most significant economic pests of citrus worldwide. This insect vectors three phloem-restricted bacteria in the genus Candidatus Liberibacter that cause huanglongbing (citrus greening), the most severe disease limiting citrus production worldwide. We examined the external morphology of the antennal sensilla of male and female D. citri using scanning electron microscopy (SEM) and determined the putative functions of the identified sensilla using transmission electron microscopic (TEM) techniques. The filiform antennae of D. citri were of the conventional type comprised of a basal scape, pedicel and a long, thread-like flagellum, which is composed of eight flagellomeres. Eleven morphologically unique sensillar types were found and described on the antennae of male and female D. citri. Of those identified, the two apical setae, multiporous types I and II sensilla trichoidea, and the antennal rhinaria were porous and may be involved in perception of host- and mate-related volatile chemicals. However, the aporous types I, II and III sensilla trichoidea may have mechanosensory functions and the chaetica sensilla, cavity sensilla and unidentified uniporous sensilla may be involved in proprioception, thermo-hygroreception and cold detection, respectively. The shape, external morphology and array of sensilla on the antennae of male and female D. citri were similar. The only major difference observed was in the morphology of the short apical setae, whose tips were recessed inward in females but not so in males. The results are discussed in relation to plausible roles of the identified sensilla in mate and host location by this species.     

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.     

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.     

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.     

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.     

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.     

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.     

Mouthparts of Megaselia scalaris (Loew) (Diptera: Phoridae)

Mouthparts of adult Megaselia scalaris (Loew), a fly species of medical importance, were examined using scanning electron microscopy. Sexual dimorphism of the labellum was observed in the mouthpart structures of this species. The labella of males were clothed with a dense covering of microtrichia, but these were found to be entirely absent from the labella of females. Aside from this difference, trichoid and conical sensilla that are most likely used as taste or contact chemoreceptors appear on the labellum and labrum of both sexes. In addition, five pairs of sharply pointed teeth at the ventral surface of the labellum is another feature that is shared by the two sexes. A plausible feeding mechanism for this fly is also advanced.     

Antennal morphology, structure and sensilla distribution in Microplitis pallidipes (Hymenoptera: Braconidae)

Microplitis pallidipes (Hymenoptera: Braconidae) is an important larval parasitoid of noctuid larval pests. In this study, we describe the morphology, ultrastructure and distribution of sensilla on the antennae of both male and female adults using scanning electron microscopy; complemented with transmission electron microscopy. Observations determined that the antennae of M. pallidipes were threadlike and the flagella were composed of 16 sub-segments. Totally, there were six types of sensilla found on the antennae. They were identified as Sensilla trichodea, Sensilla chaetica, Sensilla basiconica type I, S. basiconica type II, Sensilla coeloconicum, and elongated Sensilla placodea, respectively. The S. trichodea were the most abundant sensilla and distributed over the entire antennae, while S. basiconica I and II, S. coeloconicum, and elongated S. placodea were limited to the flagellum. S. chaetica were found on the scape and pedicle in very low numbers. The S. basiconica II and elongated S. placodea walls were full of pores as evident in transmission electron micrographs. Though the shape and structure of antennae between male and female adults were not basically different, the length and width of the antennae on male wasps were significantly greater than that of females. Also, the number, size and density of S. placodea of the male were significantly greater than those of females. The morphology and structure of these sensilla were compared with that found in other braconid wasps. Their possible functions are discussed in light of previously published literature.     

Sensilla on the antennal funiculus of the blow fly, Protophormia terraenovae (Diptera: Calliphoridae)

The morphology of the antennal funiculus and the external morphological characteristics and distribution of sensilla of blow fly, Protophormia terraenovae, have been studied using light and scanning electron microscopy. Cross section of the funiculus is roughly triangular in shape, with an anterior-medial, anterior-lateral, and posterior surface. The latter presents some large-size pits on restricted lateral and median areas of the proximal funiculus, and several smaller-size ones close to the pedicel-funiculus joint. The entire surface of the antennal sub-segment appears densely populated by microtrichia and is inhabited by seven types of sensilla: one trichoid, two basiconic, one auriculate, one coeloconic, and two basiconic-like pit sensilla. Trichoid, basiconic, auriculate and basiconic-like types display a multiporous wall, a feature characteristic of insect olfactory sensilla. It remains to be verified whether or not the coeloconic structure type has wall pores. The most abundant sensilla are the trichoid ones, which are followed by the basiconic, coeloconic and auriculate types in a decreasing density order. The basiconic-like pit sensilla are present only on the posterior funicular surface, unlike the remaining ones which populate the entire sub-segment. The blow fly' funiculus displays a significant, even though moderate sexual dimorphism, the female sub-segment being bigger and presenting a higher number of trichoid and auriculate sensilla. The presence of multiple wall pores in most of sensilla types implies an olfactory modality for sensory neurons they accomodate, thus indicating that the blow fly' funiculus is a plain olfactory organ.     

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.