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.     

Morphology and ultrastructure of the venom apparatus in the endoparasitic wasp Pteromalus puparum (Hymenoptera: Pteromalidae)

The venom apparatus of the endoparasitic wasp Pteromalus puparum (Hymenoptera: Pteromalidae) was studied with light and electron microscope and was subjected to the electrophoretic and immunohistochemical analyses. Typically its venom apparatus consists of an unbranched venom gland and a venom reservoir, which is associated with a Dufour gland. The venom gland is lined by a series of secretory units. Each secretory unit comprises a secretory cell and a duct cell. The secretory cell is associated with an end apparatus to collect its secretions into the gland lumen. Secretory cells in the venom gland are characterized by extensive rough endoplasmic reticulum and numerous electron-dense vesicles in the distal and middle parts. They also exhibit several secretory granules and vacuoles. The venom reservoir presents three distinct regions: an external layer, composed by numerous fine muscle fibers; an internal layer, represented by epithelial cell with large nucleus; and an intima portion, represented by thin and uniform organization. The morphological aspect of numerous well-developed organelles responsible for protein generation observed is in agreement with the electrophoretic and immunohistochemical results which reveal that the rich proteinaceous components are present in the venom gland and venom reservoir. The venom proteins are first mainly produced in the secretory unit of venom gland, then drained to the lumen through the end apparatus, and are finally collected and stored in the venom reservoir.     

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.     

Ultrastructural observations on antennal sensilla of Coleophora obducta (Meyrick) (Lepidoptera: Coleophoridae)

Coleophora obducta (Meyrick) is an important defoliator of larch in northeast China. To further describe the mechanism of insect-plant chemical communication, we observed the antennae and their sensilla of C. obducta by scanning and transmission electron microscopy. In both sexes, antennae were threadlike, and in total there were eight types of sensilla found on the antennae: Sensilla placodea, Sensilla basiconica, Sensilla coeloconica, Sensilla styloconica, Sensilla trichodea, Sensilla squamiformia, Sensilla furcatea and Böhm bristles, respectively. We described ultrastructures and discussed possible functions. We inferred from their ultrastructures as chemoreceptors that S. placodea, S. basiconica and S. trichodea were innervated by sensory neurons. The neuron of S. styloconica terminated in a tubular structure which suggested gustatory/mechanosensory function, and the terminal sensory pegs might function as contact-chemoreceptors depending on their locations.     

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.     

Scanning electron microscopy of legs of two species of sucking lice (Anoplura: Phthiraptera)

Pretarsal, tarsal and tibial structures of the forelegs, midlegs and hindlegs of Pediculus humanus of humans and of Haematopinus apri Goureau, 1866 (Phthiraptera), a parasite of feral hogs, were studied using light microscopy and scanning electron microscopy. Details of the tibial thumb-like process (tl) with the spine of the thumb (spn), tarsal apophysis (ta) and the coupled finger-like process (cfl) can be observed in the leg photomicrograph of both species. A frontal view of the leg in open position shows the articulation of the claw: the structures of an open-closed system, a tooth row (te), rack-system (rs) and two telescopic columns (tc) which are present near the base of the claw in both species. In H. apri, we observed a pad-like structure, the flap-like tibial lobe (fl) on the ventral surface on the tarsus, the euplantulae, with several sensilla basiconica, which is present in each leg.     

Scanning and transmission electron microscopy studies on a model series of spherulitic segmented polyurethanes

Scanning (SEM) and transmission (TEM) electron microscopy studies were made on a model series of four segmented polyurethanes. The morphologies of both the homopolymers and of their mixtures were made by SEM while TEM was utilized to study only ultrathin films of the homopolymers. It was found that well-structured spherulitic morphologies could be induced in these systems and their mixtures, and that control over the textures could be maintained by solution casting conditions. The domains were observable via TEM, and the general orientation of this structure within the spherulites was noted. Deformation studies of the spherulitic textures were followed by both SEM and small-angle light scattering. It was concluded that, in general, the spherulites deform in a nonaffine manner–this is particularly true for the systems possessing a porous texture.     

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 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.     

Scanning electron microscopy of Antarctophthirus microchir (Phthiraptera: Anoplura: Echinophthiriidae): studying morphological adaptations to aquatic life

The members of the Family Echinophthiriidae (Phthiraptera: Anoplura) are unique among insects because they infest hosts with an amphibious lifestyle. During their evolution they developed morphological traits that are reflected in unique features. The SEM is a helpful tool to analyze them. Knowing in detail the external structure of these lice is the first step to understand the whole process that derived from the co-adaptation of lice and pinnipeds to the marine environment. For the first time, we studied the external structure of all stages of an echinophthiriid louse. The results are discussed in the light of their evolutionary, functional, and ecological implications.     

The preimaginal stages and development of Spalangia cameroni Perkins (Hymenoptera: Pteromalidae) on Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)

The development and morphology of the immature phases of Spalangia cameroni Perkins, 1910 (Hymenoptera, Pteromalidae) are described from a laboratory rearing culture maintained on Ceratitis capitata (Wiedemann, 1824) (Diptera, Tephritidae), using microscopic techniques, including light and scanning electron microscopy. The surface of the chorion of the egg is smooth and the micropyle occurs at the anterior end. The immature larvae are similar to the mature larva, differing mainly in the size of the head capsule and mandibles. The mature larva displays tubercules on the body segments as well as a pleurostoma and superior and inferior mandibular processes. On completion of its larval development, an adecticous and exarate pupa is produced. The mandibles of the pupa, as for the adult, are toothed. Three larval instars are recorded based on statistical analyses of the sizes of the larval mandibles and head capsules, in combination with such characters as the number of exuviae and excretion of the meconium. There are significant positive correlations between mandible length and width of larval head capsule with the number of instars, thus indicating that the mandible length and width of larval capsule are good predictors of the number of instars in this parasitoid. Developmental time from egg to adult emergence was ～33–34 days for females and ～28–29 days for males at 21–26 °C, 55–85 RH and a L16:D8 photoperiod. Our results show that the eggs and different instars of S. cameroni can be unambiguously identified only by SEM. Therefore, characterization of the immature stages of Spalangia species using SEM should be done before subsequent routine identifications using a binocular microscope or stereomicroscope.     

Scanning tunneling microscopy studies of temperature-dependent etching of diamond (100) by atomic hydrogen

We present a technique for obtaining atomic resolution ultrahigh vacuum scanning tunneling microscopy images of diamond (100) films, and use this technique to study the temperature dependence of the etching of epitaxial diamond (100) films by atomic hydrogen. We find that etching by atomic hydrogen is highly temperature dependent, resulting in a rough and pitted surface at T approximately 200 and 500 degrees C, respectively. At T approximately 1000 degrees C etching results in a smooth surface and is highly anisotropic, occurring predominantly in the direction of dimer rows. This observation supports recent theoretical models that propose anisotropic etching as the mechanism for the growth of smooth diamond (100) films.     

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.     

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.     

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.