D3256: Olfaction and Asphondylia borrichaie: Host fidelity in a sympatrically diverging fly

Asphondylia borrichaie is a small fly (Diptera: Cecidomyiidae) that is currently undergoing host-associated sympatric divergence. Previous studies indicate that A. borrichaie consists of two host- associated populations based on its original host plant Borrichia frutescens (Asterales: Asteraceae), and another one from the two Iva species (I. frutescens (Asterales: Asteraceae) and I. imbricata (Asterales: Asteraceae)). Differences in development time suggest allochronic isolation as the primary mechanism promoting host-associated sympatric divergence of midge populations and A. borrichiae has been shown to display fidelity to its natal host plant genus (e.g. Borrichia vs. Iva). In the current study, olfactometery trials utilizing field-collected galls/midges demonstrated a weak association for a midge’s natal host; overall midges chose their natal host plant 56.1% percent of trials compared to 43.9% for the alternative (novel) plant. However, no significant differences were found in the time taken for a midge to choose natal vs novel host. Moreover, male midges showed a stronger preference for their natal host genus than females suggesting that gene flow between host-associated populations is more likely to be limited through males than females. Although clones of B. frutescens (collected from different localities) exhibited significant differences in leaf size (but not number of serrations after more 18 months of being cultured in a common greenhouse environment, suggesting at least a partial genetic control for leaf morphology, no association was detected for midges to their specific clone of B. frutescens from the midge’s natal locality.