Interaction between visual and olfactory cues during host finding in the tomato fruit fly Neoceratitis cyanescens

Herbivorous insects searching for a host plant need to integrate a sequence of multimodal sensory inputs. We conducted a series of no-choice experiments in a laboratory wind tunnel to examine the behavioral response of the specialist fruit fly, Neoceratitis cyanescens (Diptera: Tephritidae), to host visual and olfactory stimuli presented singly or in combination (e.g., colored fruit model with or without host fruit odor). We also studied the influence of wind flow, age, and sex on the response of flies. In two-choice experiments, we evaluated the ability of mature females to discriminate between two fruit models emitting host vs. non-host fruit odor or clean air. Neoceratitis cyanescens mature females can use independently or interactively olfactory and visual stimuli to locate their host, whereas immature females and males respond primarily to host fruit odor. In the absence of wind, mature females mainly use visual information to locate the host fruit. In wind, host fruit odor significantly increases the probability and speed of locating the host fruit. In a two-choice situation between two bright orange spheres, flies accurately detected the sphere emitting host fruit odor vs. non-host fruit odor or odorless air. Nevertheless, they preferred to land on the bright orange sphere when the sphere emitting host fruit odor was blue. Furthermore, when odor source and fruit model were spatially decoupled (90 or 180 degrees ), >50% flies that landed on the fruit model initially performed an oriented flight toward the odor source, then turned back to the fruit model while in flight or after one landing, thus suggesting visual information to be the ultimate indicator of host fruit.