Intra- and inter-specific communication in Drosophila suzukii: from genome to behavior

Drosophila suzukii (Diptera: Drosophilidae), an invasive pest from Asia, colonized US and Europe in 2008 and since then has economically damaged multi-million commercial fruit production. With fruit-breaking serrated ovipositor the female lays eggs in the unwounded ripening fruits making them unmarketable. To know the genetic likelihood of D. suzukii with other Drosophila species its genome and transcriptome were sequenced. The whole genome was mined to understand the origin, speciation and adaptation and was correlated with the ecology of the species. Genomic analyses revealed that D. suzukii is adapted to temperate climate and has lower selective pressure and gene-sequencing rate compared to its sibling sp. D. biarmipes. From the genomic and ecological studies, one of the objectives was to understand the role of olfaction in host fruit recognition and identify key volatile compound/s involved in female decision-making for oviposition on fresh fruits. Based on gas chromatography mass spectrometer (GC-MS) and GC-electro-antennal detector activity, isoamyl acetate was found to be one of the key compounds involved in the oviposition site selection. The phylogenetic analysis revealed that D. suzukii not only possess the full repertoire of genes encoding olfactory receptors activated by isoamyl acetate in D. melanogaster, but showed that Or67a (Or67a1 to Or67a5) is even represented by duplicated copies. Another aim was to investigate the pheromone communication in this species. The extraction and identification of cuticular hydrocarbons from the males inherently showed that the species trans-evolved by terminating the production of sex pheromone cis vaccenyl acetate (cVA), which is used by species throughout melanogaster group, but able to smell it with ‘fewer’ T1 sensilla. Being under highly selective pressure D.suzukii has i) scaled-down the size of ejaculatory bulb in males, ii) fewer T1 tricoid sensilla, and iii) comparatively smaller glomerulus, in the antennal lobe (AL), involved in receiving sensory impulses from T1 sensilla when compared to D. melanogaster. However D. suzukii shares all functional fatty acid synthase (FAS) genes responsible to CH production. On applying D. melanogaster male equivalent synthetic cVA on males of D. suzukii, it significantly reduced the mating acceptance in the females, which otherwise increased in D. melanogaster. Therefore, by adapting not to produce cVA as a sex pheromone D. suzukii tend to avoid competition with congeneric species for oviposition. The whole spectrum of the present and future studies would help to understand the evolution of the olfactory code among the closely related species of Drosophila and, as a consequence, contribute to develop alternative control methods of D. suzukii. Indeed, comparison of D. suzukii with sibling species and D. melanogaster could shed light on the evolution of ecological innovations and help researchers in understanding what makes a species to be an invasive pest