Phytochemical male attractants are ‘Red Bull’® for Bactrocera fruit flies (Diptera: Tephritidae): Trascriptome evidences for male competitive ability

Monitoring and control of Bactrocera fruit flies largely dependent on male attractants or lures: the most common male lures are methyl eugenol, raspberry ketone (its synthetic analogue cue lure) or zingerone. Males show strong and positive olfactory and gustatory response to one of these plant-derived chemicals thus used in management through a lure-and-kill approach. Despite their applied importance however, the evolutionary and functional significance of lures in natural history of Bactrocera flies remain enigmatic. Males that have imbibed the lures commonly have a mating advantage over unfed males, presumably by releasing more attractive pheromone volatiles and subsequent selection by females for copulation. However, the male lures raspberry ketone and zingerone are also known, in a diverse range of other organisms, to be involved in increasing energy metabolism.  If this also occurs, then this may represent an additional benefit to males as courtship is metabolically expensive and lure feeding may increase a fly’s short term energy. Here we tested this hypothesis by performing comparative RNA-seq analysis between zingerone fed and unfed with Bactrocera tryoni.  RNA-seq analysis revealed, over expression of 3193 genes including homologues transcripts regulating inter-male aggression, along with significant enrichment of several energy metabolic pathways. These results suggest that feeding on these secondary plant compounds leads to complex, but likely short term physiological changes in the flies which result in a male which is more competitive.