Submitted to: Journal of Insect Behavior
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/31/2014
Publication Date: 4/30/2014
Citation: Kuenen, L.P., Gilbert, C., Siegel, J.P. 2014. Flying slower: Floor pattern object size affects orthokinetic responses during moth flight to sex pheromone. Journal of Insect Behavior. 27:581-592. Interpretive Summary: The mechanisms an insect uses to locate a distant odor source such as a mate or food source include control of its speed and steering while maintaining at least intermittent contact with the source’s odor plume and its visual surroundingds to detect flow direction of the odor plume. The algorithms controlling these parameters are of interest to entomologists, behaviorists, and the Defense Department. Here we tested the effect of a series of small-to-medium-sized visual cues on the moths flight performance while flying upwind along a sex pheromone plume to its source. We found that the moths reduced their upwind speed as the visual cues became larger but they did not substantially alter any other aspect of their flight control mechanisms. This suggests that the moths slow down as they approach the perching site of female moth to better locate her at close range. These results will assist behaviorists and neurophysiologists continue to piece together the algorithms for odor source location. The results will also be of continuing interest to the Defense Department as increased understanding of these mechanisms will aid in the continuing development of autonomous vehicles for locating odor sources such as explosives or chemical leaks.
Technical Abstract: Previous studies with Oriental Fruit Moth (OFM, Grapholita molesta) and Heliothis virescens males flying upwind along a pheromone plume showed that they increased their upwind flight speed as they flew higher above striped floor patterns and, for OFM, to a similar degree over dotted floor patterns. This response pattern has been demonstrated in another moth species, Epiphyas postvittana, and in a beetle, Prostephanus truncatus. In all cases, the change in apparent size of the wind tunnels’ ventral floor pattern objects was ignored as a contributing factor to the changes in flight speed. Here, a systematic examination of moths’ flight control over different sizes of transverse stripes and dot patterns ranging down by halves from 5 cm to 0.625 cm and a blank white floor as a control, showed that OFM males fly faster upwind and along their flight paths over floor patterns of decreasing size. Increased speeds over striped patterns were evident as stripe width decreased below 2.5 cm, whereas moths did not increase their flight speed over dot patterns until dot size had decreased to less than 1.25 cm. Another flight component that the moths can actively control, their course angles, was unchanged among above both patterns, except for moths flying over 5 cm stripes. Turning frequency and interturn distances were mostly unchanged or offset each other, negating any effects on upwind progress. As in an earlier study examining flight speeds at three heights above floor patterns of three densities, the moths’ changes in speed appear to be exclusively affected by changes in their orthokinetic response to the size of the floor patterns.