REITERATIVE RESPONSES TO SINGLE STRANDS OF ODOR PROMOTE SUSTAINED UPWIND FLIGHT AND ODOR SOURCE LOCATION BY MOTHS

We characterized single upwind surges of flying male Heliothis viresce ns moths in response to individual strands of pheromone generated expe rimentally in a wind tunnel. We then showed how this surge functions i n this species as a basic 13.4-cm, 0.38-sec-long building block that i s strung together repeatedly during typical male upwind flight in a no rmal pheromone plume. The template for a single iteration, complete wi th crosswind casting both before and after the straighter upwind surgi ng portion, was exhibited by males flying upwind to pheromone and expe riencing filament contacts just frequently enough to produce successfu l upwind flight to the source, as hypothesized by an earlier model. Al so as predicted, with more frequent filament contact by males, only th e straightest upwind portions of the surges were reiterated, producing direct upwind flight with little crosswind casting. Electroantennogra m recordings made from males in free flight upwind in a normal point s ource pheromone plume further support the idea that a high frequency o f filaments encountered under the usual pheromone plume conditions pro motes only these repeated straight surges. In-night electroantennogram recordings also showed that when filament contacts cease, the casting , counterturning program begins to be expressed after a latency period of 0.30 sec. Together these results provide a plausible explanation f or how male and female moths, and maybe other insects, fly successfull y upwind in an odor plume and locate the source of odor, using a surgi ng-casting, phasic-tonic response to the onset and disappearance of ea ch odor strand.