Evolution of the molecular mechanisms of pheromone reception in European and Asian corn borer moths
Allen, Jean Elaine.
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The insect order Lepidoptera includes more than 180,000 species and some of the most well known pests of food and fiber crops. Ninety-eight percent of lepidopteran species belong to a taxonomic group called the Ditrysia. Modern Ditrysia use long distance sex pheromones to facilitate mating. The European corn borer, Ostrinia nubilalis (ECB) is a well known pest of agricultural crops throughout North America and Western Europe. The European corn borer species exists as two different pheromone races. Females of the species produce, and males are attracted to different blends of the isomers (Z)-11-tetradecenyl acetate and (E)-11-tetradecenyl acetate. The closely related Asian corn borer (O. furnacalis, ACB) has evolved to use a pheromone blend that is unique among all Lepidoptera, (Z)- and (E)-12-tetradecenyl acetate. O. nubilalis and O.furnacalis species can be used as models to study pheromone evolution. Pheromones are detected at the periphery of the olfactory system by olfactory sensilla located on the antennae. Proteins involved in pheromone detection at the periphery include: odorant receptors, pheromone binding proteins, and sensory neuron membrane proteins. In this study, the coding sequences of seven odorant receptors, five pheromone binding proteins, and two sensory neuron membrane proteins were cloned from Asian and European (E and Z race) corn borer antennae. Five odorant receptors and two pheromone binding proteins were expressed at high levels in male corn borer antennae based on quantitative real-time PCR assays. Several odorant receptors were heterologously expressed in Xenopus laevis oocytes, and odorant receptor 6 was found to respond specifically to (Z)-11-tetradecenyl acetate in electrophysiological studies. The coding sequences of all fourteen genes were analyzed by computational and statistical methods to identify candidate genes that may play a role in the detection of the ACB pheromone blend. Odorant receptor 3 and pheromone binding protein 3 may have evolved specificity to 12-tetradecenyl acetates. Future studies will clarify the role of these proteins in the evolution of pheromone detection at the molecular level. An improved understanding of the evolution of pheromone detection may lead to new pheromone based controls for these economically damaging species.