Structure and distribution of antennal sensilla in Pseudosymmachia flavescens (Brenske) (Coleoptera: Scarabaeidae: Melolonthinae)

Abstract

Morphology, microstructure, and distribution of antennal sensilla were compared between female and male Pseudosymmachia flavescens (Brenske) (Coleoptera: Scarabaeidae: Melolonthinae). Lamellate antennae of P. flavescens were shown to have typical scape, pedicel, and flagellum segments. The flagellum consists of a four‐segmented funicle and a three‐segmented club. The lengths of their pedicel and funicle were found to be similar in females and males. Distinct sexual differences were observed in the length of lamellar segments. Nine types/subtypes of sensilla were identified on the antennae of both sexes, including Böhm sensilla, sensilla trichodea, sensilla basiconica (SB), and two subtypes for sensilla chaetica, sensilla coeloconica, and sensilla placodea each. Olfactory sensilla (e.g., SB and placodea) are mainly located on three lamellar segments of the antennal club. Variation was also seen in abundance of various types of antennal sensilla, with males possessing significantly more sensilla than females. Sensilla placodea were the most abundant, and their number in males was twice of that in females, showing a clear sexual dimorphism. The difference in the distribution of sensilla placodea might reflect their roles in sexual chemical communication.

Characterisation of Antennal Sensilla and Electroantennography Responses of the Dung Beetles Bubas bison, Onitis aygulus and Geotrupes spiniger (Coleoptera: Scarabaeoidea) to Dung Volatile Organic Compounds

“…This differential odour sensitivity could potentially be attributed to the differential distribution of olfactory receptors responding to chemical cues. As an example, the middle lamella of the scarab beetle Pseudosymmachia flavescens (Coleoptera: Scarabaeidae: Melolonthinae) generated higher EAG responses than those of the proximal or distal lamella and the closed antennal club, which was found to have a significant correlation with the density of sensilla placodea in a previous study [27,62]. Single sensillum recordings (SSRs) have shown that olfactory neurons housed in densely arranged sensilla basiconica in G. auratus were sensitive to indole, skatole, phenol and p-cresol, while a separate group of olfactory cells responded specifically to butanone [28,48].…”

“…Therefore, sensilla type, density and distribution on antennae may impact the sensitivity profile for odorant molecules. Although the antennal morphology and sensilla structure have been characterised in many coleopteran families, the antennal sensory apparatus of dung beetles is still poorly understood [26,27]. Only a few studies have investigated the morphology and distribution of antennal sensilla in dung beetles, specifically Geotrupes auratus, Copris pecuarius [28], Typhaeus typhous, Onthophagus fracticornis and Aphodius fossor [29].…”

“…Selection pressure on the insect may have resulted in species-specific olfactory mechanisms by which different insects process information. Therefore, the potential of a compound to signal as a background odour or a resource-indicating odour and the distribution and abundance of olfactory receptors may vary based on the beetle species and their ecological niche [27,29,[43][44][45].…”

Abundance and distribution of antennal sensilla on males and females of three sympatric species of alpine grasshopper (Orthoptera: Acrididae: Catantopinae) in Aotearoa New Zealand

“…Paprides nitidus antennae are also shorter and have signi cantly smaller segments than those of S. australis.In many grasshopper species males have more sensilla on their antennae than females (80% of 75 species examined byBland 1989, Chen et al 2003and Li et al 2007). These sexual differences are attributed to sexual selection on males to have high sensitivity to pheromones released by females(Chen et al 2003;Malo et al 2004;Wee et al 2016;Li et al 2021b). As the New Zealand alpine grasshoppers tend to be visually cryptic (to avoid visual predators) and do not generate acoustic signals with wings when searching for mates…”