Neuroanatomical and electrophysiological studies of identified contact chemoreceptors on the ventral ovipositor valve of 3rd instar larvae of lubber grasshoppers (Taeniopoda eques)

Morphological and genetic differences in legs of a polygamous beetle between sexes, Glenea cantor (Coleopter: Cerambycidae: Lamiinae)

The legs of insects play an important role in their daily behaviour, especially reproduction. Entomologists have performed much research on the role of the leg in different behaviours of beetles, an important group in the insect family, but relatively little has been done to study the ultrastructure and transcriptome of their legs. Hence, we systematically studied the ultrastructure and gene expression of the leg of G. cantor, a polygynous beetle, and compared its male and female diversity. In this study, we found the fore-leg, mid-leg and hind-leg of the female were significantly longer than those of the male. From the perspective of intuitive structural differences, we also compared the ultrastructures of the adhesion structure (tarsal) of males and females. The tarsal functional structure of the adult leg mainly includes sensilla and an adhesion structure. The sensilla on the tarsal joint mainly include sensilla chaetica (SCh II, SCh III) and sensilla trichodea (ST II). The adhesion structure includes disc-shaped bristles (di), lanceolate bristles (la), serrated bristles (se), spatula-shaped bristles (spl) and mushroom-shaped bristles (mus). Although there was no significant difference in sensillum distribution or type between males and females, there were significant differences in the distribution and species of adhesion structures between the fore-leg, mid-leg, and hind-leg of the same sex and between males and females. Therefore, different adhesion structures play different roles in various behaviours of beetles. On the other hand, the transcriptome results of male and female legs were screened for a subset of olfaction- and mechanics-related genes. We discovered that the male leg showed upregulation of 1 odorant binding protein (OBP), 2 Olfactory receptors (ORs) and 2 Chemosensory proteins (CSPs). Meanwhile, the female leg showed upregulation of 3 OBPs, 1 OR, 1 Gustatory receptor (GR) and 3 Mechanosensitive proteins (MSPs). An in-depth examination of the ultrastructure and molecular composition of the legs can elucidate its function in the reproductive behavior of G. cantor. Moremore, this investigation will serve as a cornerstone for subsequent research into the underlying behavioral mechanisms.

Cuticle protein gene LmCP8 is involved in the structural development of the ovipositor in the migratory locust Locusta migratoria

The ovipositor comprises the external genitalia of female insects, which plays an important role in the mating and ovipositing process of insects. However, it remains rudimentary of regional gene expression and physiological function in the ovipositor during structural development. Here, we analysed the basic structure and characteristics of the ovipositor in the migratory locust Locusta migratoria. RNA-seq analysis revealed the specialization of chitin metabolism, lipids synthesis and transport, tanning and cuticular protein genes in the ovipositor. Among them, two cuticle protein genes, LmCP8 and LmACP79, were identified, which are specifically expressed in the ovipositor. Functional analysis based on RNA interference showed that deficiency of LmCP8 affected the structural development of the ovipositor resulting in the retention of a large number of remaining unproduced oocysts in the ovary of the locusts. Our results provide a fundamental resource to investigate the structural development and physiological function of the ovipositor in L. migratoria.

Neuropathological effect of dimethyl disulfide on neurons of the desert locust Schistocerca gregaria

Botanical insecticides have introduced a new concept in insecticide research. In response to insect attacks, some plants can release volatile compounds that alter insect metabolism and nervous system activity. In the present study, changes in the electrical activity of chemoreceptors and alteration of the fine structure of metathoracic ganglia of desert locust were examined after acute exposure to dimethyl disulfide (DMDS), a sulfur compound released from Allium porrum. Animals were exposed to 1/4 LC50 of DMDS (0.375 μl/L air) and electrophysiological and electron-microscopical studies were carried out. Application of DMDS showed an increase in the activity of deterrent cells present in tarsal chemosensilla of locust. On the other hand, evident degenerative changes in the neurons, neuroglia, neuropile and synaptic vesicles were observed in the metathoracic ganglia of DMDS-treated animals. These findings revealed that pest control using DMDS might be feasible and future work is highly recommended in this respect.

Abdominal sensory equipment involved in external host discrimination in a solitary parasitoid wasp

Already parasitized hosts are often of poorer quality than healthy hosts. It is therefore usually advantageous for parasitoid females to recognize and reject them. Parasitized hosts can be identified on the basis of various physical or chemical marks present on the surface or inside the hosts or their surroundings in the case of concealed host. Here we studied host discrimination behaviors of females of a certain population of Pachycrepoideus vindemmiae, a solitary ectoparasitoid, which are known to reject large-sized parasitized hosts after an abdominal examination of their surface. We first investigated females' recognition behaviors of host parasitism status when confronted to small-sized hosts (Drosophila melanogaster pupae) as host size may influence the use of different cues for host selection. We showed that, in such a situation, females also discriminate parasitized hosts after an external host exploration with the tip of their ovipositor sheath (third valvulae). We then described the sense organs present on the different parts of the ovipositor by means of scanning and transmission electron microscopy analysis. As the extremity of the third valvulae bears only one type of sensilla that appears to be chemoreceptors, we considered these sensilla as highly likely to be involved in host discrimination in P. vindemmiae. To our knowledge, this is the first time that receptors located on the ovipositor sheath are described as implicated in host discrimination in parasitoid wasps. We discuss potential chemical markers that might be detected by these receptors.