Morphology of olfactory sensilla and its role in host plant recognition by Neomegalotomus parvus (Westwood) (Heteroptera: Alydidae)

Abstract

The external morphology of the sensilla, including pores and permeable points on the cuticle of the antennae of adults of Neomegalotomus parvus (West.) (Heteroptera: Alydidae) was investigated with regard to their olfactory function. Behavioural evidence of olfaction, the importance of the different antennal segments in locating the host under still-air, and the responses of the insects to plants' scents and to pheromones in wind assays were also studied. With the scanning electronic microscope mechanoreceptor sensilla were found on the four segments of the antennae of N. parvus. The density of the sensilla was greater on the 4th segment. On the apical segment, sensilla with olfactory morphological traits were observed. Bugs with intact antennae located food more frequently and faster than those with blocked or amputated antennae. N. parvus preferred intact seeds to sealed seeds, but there was no preference when the last segment of the antenna was blocked. In wind tunnel, bugs were attracted to mature and green pods, and to hexanic extract of mature pods of pigeon pea, Cajanus cajan (L.) Millsp.; there was no response to panicles of rice, Oryza sativa L. or to the male pheromone.