Antennal sexual dimorphism in Diabrotica virgifera virgifera (Le Conte) (Coleoptera : Chrysomelidae): Male specific structures, ultrastructure of a unique sensillum, and sites of esterase activity

Abstract

Morphological and histochemical studies were performed on the flagellar antennal segments of adult Diabrotica virgifera virgifera LeConte (Coleoptera : Chrysomclidae). The work was part of a program to investigate the biological significance of a soluble esterase (Est-a) found only in the antennae. Est-a was known to be produced initially it the distal flagellar segments and age-related increases in concentration have been recorded in male beetles in comparison to females. The ventral surface of the 5 distal segments of male antennae possess a field of raised, smooth cuticle having pit-like depressions. The pits contain unusual cup-shaped sensilla abundantly supplied with pore tubules, typical of those associated with olfactory processes in other species. The epicuticle of the cur) sensilla is thin but lacks the pores commonly found in olfactory sensilla. The duct of at least one dermal gland opens into each pit. When sectioned antennae were stained fcr general esterase activity, it was the cells of the dermal glands that stained positive. The pit fields are unique to males. However, cup sensilla and dermal glands with esterase activity are present on female antennae and at sites outside the pit fields on male antennae. Circumstantial evidence suggests that the observed sensillum type functions in olfaction. The sensilla and associated glands in the pit fields of males may be involved in detection of the female-produced sex pheromone, 8-methyl-2-decyl propanoate.