Ecological specialization is an important driver of diversity, and nowhere is diversity higher than in the tropics. The tropical fruit fly, Blepharoneura, a genus in the economically important family of true fruit flies (Tephritidae), demonstrates an escalated pattern of diversity. These insects are extreme specialists. All Blepharoneura species feed on plants in the Cucurbitaceae, and most feed only on a single plant species. Blepharoneura species are also specific to plant parts: stems, seeds, or specifically male versus female flowers. The fly larvae feeding deep within the floral tissues are preyed on by parasitoid wasps, which are also highly specific in their host choice. For example most species of the parasitoid wasp Bellopius successfully kill just a single species of Blepharoneura on a single flower sex of a single plant species. Bellopius attacking the “wrong” species of Blepharoneura do not survive. This tritrophic study aimed to identify mechanisms of host-detection for these insects. Floral volatiles were collected from male and female flowers on intact plants from six plant species in two genera: Psiguria and Gurania growing wild in Trinidad and Ecuador and analyzed using gas chromatography mass spectrometry (GC-MS) to identify the host plant volatiles. In this way we were able to determine what unique volatile signals flowers release, in order to demonstrate whether Blepharoneura spp. can use these fragrances in selecting their host plant, and/ or if the parasitoid wasps use the scents as signals to find the fly larvae.
Results/Conclusions
More than 50 compounds, including aromatic compounds, terpenoids, aldehydes, alcohols and esters, were detected in the samples. We found scent profiles unique to plant species, indicating that floral volatiles could be used to differentiate between them. Infestation levels were highest in inflorescences of Gurania spinulosa in Trinidad. We found that infestation increased specific plant volatiles in inflorescences of male G. spinulosa. This increase could potentially be “a cry for help” to attract parasitoid wasps in response to infestation of their floral tissues by Blepharoneura larvae. Importantly, one of the compounds found in increased concentration in highly infested plants was methyl salicylate; a compound widely employed by predators and parasitoids during host-finding behavior. This study identifies certain candidate compounds that could be used by both the flies in selecting host plants, and the wasps in locating the Blepharoneura flies.