Diversity and distribution patterns of antennal sensilla in Hydropsychidae (Insecta, Trichoptera)

Structure and distribution of antennal sensilla were studied in males of 19 species of the caddisfly family Hydropsychidae by using scanning electron microscopy (SEM). Eleven types of sensilla were found: long trichoid, chaetoid, thick chaetoid, curved trichoid, coronary, basiconic, styloconic and four types of pseudoplacoid sensilla (mushroom-like, auricillic, ribbed, and T-shaped). Thick chaetoid, ribbed pseudoplacoid, and T-shaped pseudoplacoid sensilla were found only in Macronematinae. The great diversity of pseudoplacoid sensilla originated from a mushroom-like type, which also has a variable structure. Basal flagellomeres in the majority of studied species are equipped with ventrally positioned sensory fields of curved trichoid sensilla. In contrast to Arctopsychinae and Hydropsychinae, the increased number of these sensilla in the fields was noted for Diplectroninae and Smicrideinae. Most Macronematinae show a reduction of sensory fields and a strongly decreased average number of curved trichoid sensilla on distal segments. The great differences found in the studied family probably indicate a rapid function-related evolution of the antennal sensory surface structures in the caddisfly family Hydropsychidae.

Morphological and Ultrastructural Characterization of Antennal Sensilla and the Detection of Floral Scent Volatiles in Eupeodes corollae (Diptera: Syrphidae)

The olfactory sensing system of the syrphid fly Eupeodes corollae is essential in pollination and prey localization, but little is known about the ultrastructural organization of their olfactory organs. In this study, the morphology, distribution, and ultrastructural organization of antennal sensilla of E. corollae in both sexes were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Neuronal responses of a subtype of sensilla basiconica to floral scent compounds were recorded by single sensillum recording (SSR). Ten morphological types, including Böhm bristles, sensilla chaetica, microtrichiae, sensilla trichodea, sensilla basiconica, sensilla clavate, sensilla coeloconica, sensilla styloconica, sensilla placodea, and sensory pit, were identified. Except for Böhm bristles and sensilla chaetica, which were distributed on the scape and pedicel of E. corollae antennae, innervated sensilla were densely distributed on the flagellum, a vital sensory organ. Further, observing ultrastructural organization showed that the sensilla trichodea, basiconica, and clavate are single-walled with multiple nanoscale pores perforating the cuticle. Sensilla coeloconica are double-walled and have no wall pores, but instead, have longitudinal grooves along with the pegs. Sensilla chaetica, Böhm bristles, and microtrichiae did not have wall pores on the cuticle or sensory cells at the base. The SSR results indicated that neuron B housed in the subtype of sensilla basiconica I (SBI) mainly responded to methyl eugenol and other aromatic compounds. Overall, our results provide valuable information to understand the morphology and ultrastructure of antennal sensilla from E. corollae. These findings are beneficial for the studies of the neuronal function map of olfactory sensilla and for determining evolutionary relationships in Diptera.

Morphology of the Antennal Sensilla of Notonectoidea and Comparison of Evolutionary Changes in Sensilla Types and Distribution in Infraorder Nepomorpha (Insecta: Heteroptera)

This article introduces the results of a study of three families of Nepomorpha and is the last part of a series of studies that sums up our work on the morphologies of the antennal sensory structures in this taxon. The morphologies and distribution of the sensilla in the families Notonectidae, Pleidae and Helotrephidae were studied under a scanning electron microscope. Six main types (sensilla trichodea, chaetica, campaniformia, basiconica, ampullacea and coeloconica) and ten subtypes (five subtypes of sensilla trichodea and five subtypes of sensilla basiconica) were described. The results were compared with other studies on the antennal sensilla of Nepomorpha in order to assess evolutionary changes within the infraorder. With the use of cladistics analysis, the monophyly of the families Nepidae, Micronectidae, Corixidae and Gelastocoridae was supported. On the other hand, the occurrence of some clades forming superfamilies was weakly supported by bootstrap analysis. These results, supported by presence of the numerous autapomorphies, suggest that antennal sensilla evolved within inner groups.

Ultrastructure of the Sensilla on the Antennae and Mouthparts of Bean Weevils, Megabruchidius dorsalis (Coleoptera: Bruchinae)

Megabruchidius dorsalis (Fåhraeus, 1839) (Coleoptera: Bruchinae) is an important pest that damages the seeds of Gleditsia L. (Fabaceae: Caesalpinioideae). This beetle searches for host plants with its sensory system. To further explore the mechanisms of host location and to understand the ultrastructure of M. dorsalis, we examined the morphology and distribution of its sensilla on the antennae and mouthparts of male and female adults, using scanning electron microscopy (SEM). Both male and female antennae are serrated and can be divided into scape, pedicel, and flagellum. There were seven types and eight subtypes of antennal sensilla, including Bőhm bristles (BB), two subtypes of sensilla trichoid (ST1, ST2), two subtypes of sensilla chaetica (SC1, SC2), four subtypes of sensilla basiconic (SB1, SB2, SB3, SB4), sensilla cavity (SCa), sensilla auricillica (SA), and sensilla gemmiformium (SG). Five types of maxillary and labial palp sensilla in the mouthparts were observed: sensilla chaetica (SC), sensilla trichoidea (ST), sensilla styloconica (SSt), sensilla coeloconica (SCo), and sensilla digitiform (SD). No sexual dimorphism in sensilla type was observed, but there were variations between males and females in the numbers and distribution along the antennae. There were more SA in males than in females, while the number of ST sensilla in the maxillary palps were lower in males than in females. ST1 were most abundant in both sexes. We discussed potential function related to structure via comparisons with previous investigations of bruchids and other insects. Our results provide a theoretical basis for further studies on sensory physiological function, using semiochemicals as effective biological controls of M. dorsalis.