Chemical ecology of phytophagous scarab beetles

Abstract

Sex pheromones have been characterized only for species in the subfamilies Rutelinae and Melolonthinae; aggregation pheromones have been identified for two species in the Dynastinae. Melolonthines utilize mainly amino acid derivatives and terpenoid compounds, but sex pheromones of rutelines are fatty acid derivatives. Various other species utilize japonilure-type lactones that are produced by desaturation of fatty acids, followed by hydroxylation, chain shortening, and cyclization. In marked contrast to melolonthine sex pheromone glands that are everted from the abdominal tip, ruteline sex pheromone glands consist of epithelial cells that line the inner surfaces of the pygidium and two apical sternites. Some species that are geographically and/or seasonally isolated utilize the same sex pheromone system, but chirality plays an important role in the isolation of the communication channels of two ruteline species, where one enantiomer is utilized as sex pheromone and the other is a behavioral antagonist. Olfactory receptor neurons (ORNs) are specifically tuned to these enantiomeric pheromones. It is unlikely that the specificity of these ORNs is achieved only by odorant-binding proteins. Pheromone-degrading enzymes are present in scarab beetle antennae and show considerable substrate specificity.