Effect of wind speed on the pheromone-mediated behavior of sexual morphs of the potato aphid, Macrosiphum euphorbiae (Thomas) under laboratory and field conditions.

The effect of wind on the potato aphid, Macrosiphum euphorbiae, male responsiveness to the sex pheromone, and on the calling behavior of virgin oviparae, was studied under constant wind speeds in the laboratory and in the field. A significant proportion of females called at wind speeds up to 4 m/sec, whereas male flight behavior in clean air was inhibited at velocities > 2 m/sec. However, males continued to walk over the range of wind speeds at which females called. Under constant wind velocities in a wind tunnel, males downwind of calling females oriented on the upwind edge of the release stand, and fewer individuals took flight at low constant wind speeds than in a clean air plume. In all cases, whether calling females were present or not, the males that took flight moved downwind. However, when a bridge was available, a significant proportion of males walked upwind to the pheromone source. The same orientation and walking behaviors were observed when males were placed downwind of calling females under variable wind conditions in the field. However, contrary to the laboratory results, 30% of the males tested flew upwind and landed on the source. A more detailed examination found that males orienting toward a source would walk if wind speeds were high but initiated flight in an "upwind" direction if there was a lull in wind velocity. These findings suggest that for the potato aphid, and probably for many other insect species with weak flight capacity, walking behavior is a significant component of pheromone-mediated mate location. This would permit males to continue foraging for calling females in the vicinity when wind velocities inhibit flight.