Sex pheromone biosynthesis and odorant receptors in gall midges

The gall midge family (Diptera: Cecidomyiidae) is comprised of more than 5000 species, several of which are economically important pests in agriculture. Gall midges demonstrate a great diversity in feeding habits. They are host specific and feed on only one or a few closely related plants. Gall midge infestation results in the formation of a gall, in which the midge larva extracts nutrients from the host. The intimate relationship between midge and plant is likely the main reason for the fast speciation that occurs within this insect group. Gall midges select hosts and mates by means of olfactory signals. Thus, the ecological diversity and specificity of the midges make them suitable for studies of evolution of production and detection of odor signals.

We aim to identify pheromone biosynthetic enzymes and odorant receptors (ORs) of the Hessian fly, Mayetiola destructor, a serious pest of wheat. The genome sequence already available to us, in combination with transcriptome analysis using 454 sequencing as well as functional studies of expressed genes will serve as a basis for characterization of these proteins. Since gall midge pheromones in some ways resemble lepidopteran pheromones, we want to compare the biosynthetic pathways and ORs of gall midges to lepidopteran counterparts. To study the evolution of olfactory communication within the gall midge family using a comparative approach, we also aim to identify ORs of the orange wheat blossom midge, Sitodiplosis mosellana, that uses the same host as M. destructor. The comparison will help to elucidate the evolution of host specificity and speciation among these important pest insects.