Effects of wind speed and atmospheric pressure on mate searching behavior in the aphid parasitoid Aphidius nigripes (Hymenoptera : Aphidiidae)

The effects of wind speed and atmospheric pressure on male mate searching b ehavior modulated by a female sex pheromone, were investigated in the aphid parasitoid Aphidius nigripes (Hymenoptera: Aphidiidae). Male A. nigripes g enerally did not reach females at wind speeds of 100 cm/sec, as the majorit y of individuals taking Fight in the pheromone plume (81.8%) were unable to sustain upwind flight. At lower wind velocities, male responsiveness to fe males generally decreased with distance from the source However, wind speed s approaching the upper threshold (100 cm/sec) tended to eliminate this dis tance effect. Therefore there appears to be a trade-off between the need fo r higher wind speeds to detect the pheromone source from long distances, an d a reduction in male flight capacity as wind velocity increases. OILY resu lts also indicate that chemical communication in A. nigripes could be affec ted by variations in atmospheric pressure, as we observed a relationship be tween pressure fluctuations in the 24 hr prior to testing and male responsi veness to females. The importance of these abiotic factors on mate searchin g behavior is discussed within the context of the reproductive biology of A . nigripes.