Abstract
Chemoreceptive sensilla are abundantly distributed on antennal lamellae of scarab beetles. Olfactory reception by these sensory lamellae plays a major role in feeding behaviors and sexual communication of these beetles. A new electroantennogram (EAG) recording technique is here described for evaluation of electrophysiological responses of antennal lamellae of Pseudosymmachia flavescens to sex pheromones and host plant-related compounds. EAG responses were recorded simultaneously from each lamella and the closed antennal club. All test stimuli elicited similar EAG depolarization profiles in all the three lamellae and the closed club although EAG amplitudes from the same lamella or the club varied widely among different chemical stimuli. The mid lamella tended to produce significantly greater EAG responses. EAG responses evoked by a sex pheromone component, anisole, showed a significant correlation with the density of sensilla placodea subtype 1 (SP1). However, no general patterns were obtained for correlations between the density of any test sensilla type and EAG amplitudes evoked by all the six plant volatiles. Single sensillum recordings are needed to elucidate the specific roles of these sensilla in intraspecific sexual communication and perception of host plant volatiles.
Highlights
As an important feature of living organisms, olfaction plays a key role in regulating essential behaviors
In the case of low dose, there were no significant differences in EAG responses of female lamellae to 1-hexanol and 6-methyl-5-hepten-2one
All lamellar segments of the antennal club are involved in sexual chemical communication and perception of plant volatiles (Leal, 1998)
Summary
As an important feature of living organisms, olfaction plays a key role in regulating essential behaviors. The location of mates, food sources, and oviposition sites, as well as avoidance of predators and other threats, primarily relies on olfactory perception of environmental chemical signals. The main olfactory organs in insects include antennae, maxillary palps, labial palps, ovipositor, and feet. The antennae are the most important sensory organ and their function in olfaction in insects has been commonly recognized. A variety of sensilla are distributed on the surface of the antennae, and mainly tuned to detect odorants in the environment (Altner and Prillinger, 1980; Zacharuk, 1985; Steinbrecht, 1997). The antennae of scarab beetles (Coleoptera: Scarabaeidae) are usually 10-segmented with the last 3–7 segments forming a lamellate club (Meinecke, 1975). The lamellar segments are always folded together to protect their inner surfaces when resting or crawling in soil, but wide-open during
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