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

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.

A Practical Technique for Electrophysiologically Recording from Lamellated Antenna of Scarab Beetle.

Host-plant volatiles play a key role in finding mate and suitable host plants of phytophagous scarab beetles. Hence it is immensely important to collect and identify these volatiles. The gas chromatography coupled with electroantennographic detection (GC-EAD) technique has been used as a rapid and convenient tool for the identification of physiologically active components from plants. Here, we describe a practical method for electrophysiologically recording from lamellated antenna of scarab beetles. This method enables direct electroantennogram (EAG) recordings from antennal club without damage to the antenna in a similar manner to the conventional cut-tip EAG recording technique for clavate antenna. The headspace volatiles from walnut (Juglans regia L.) trees were collected with a Poropak-Q trap at dusk and then analyzed with GC-EAD. Those volatile compounds that elicited electrophysiological responses on the antennae of a scarab beetle, Metabolus flavescens Brenske (Coleoptera: Scarabeidae: Melolonthinae) were determined by means of gas chromatography-mass spectrometry (GC-MS). The lamella directly connected to the recording electrode was held apart from the other two lamellae on the antenna with a minuten pin and a disposable syringe needle. In order to improve electrical contact, a surfactant, Tween® 80, was used to lower the surface tension of Beadle-Ephrussi Ringer solution. This study demonstrated that addition of 0.05% Tween® 80 to the Beadle-Ephrussi Ringer solution suppressed baseline noise and assured significantly greater EAG response in general. Due to its simplicity and efficiency, this method may also be useful for studying the electrophysiology of other insect species having club-like antennae.

A SEM study of antennal sensilla in Maladera orientalis Motschulsky (Coleoptera: Scarabaeidae: Melolonthinae).

The external morphology of antenna and fine structure of its sensilla of Maladera orientalis were studied using scanning electron microscopy. The antenna consists of scape, pedicel, funicle and a club composed of three lamellae. Funicle has five, sometimes, four segments. Böhm bristles, three subtypes of sensilla chaetica, one subtype of sensilla trichodea, one subtype of sensilla coeloconica, four subtypes of sensilla basiconica, and one subtype of sensilla placodea were described. No sexual differences were found in number, type and distribution of sensilla on all antennomeres. The most notable feature of sensilla on antennae of M. orientalis is the presence of long and narrow strip-like sensilla placodea on both sides of all club lamellae. These porous sensilla placodea are slightly depressed below the lamella surface and tend to lie in parallel with the lamella axe. They are similar to sensilla placodea found in hymenopteran species but very different from those round plate-like sensilla placodea occurring on the lamellae of scarab beetles.