SOME FACTORS AFFECTING PRESUMED MIGRATORY FLIGHT ACTIVITY OF THE CONVERGENT LADYBEETLE,<i>HIPPODAMIA CONVERGENS</i>(COCCINELLIDAE: COLEOPTERA)

Abstract

Hippodamia convergens migrates long distances to and from mountain-top aggregation sites. It undergoes an imaginal diapause associated with a 6-9 month aestivo-hibernation at the aggregation sites. Laboratory tethered-flight tests can be used as an assay for migratory behavior. Beetles that fly 30 min on a tether will nearly always fly much longer. Long tethered flight is pre-reproductive in females, though apparently not in males. Starvation or poor quality food will greatly enhance migratory behavior. However, the tendency to display migratory behavior is greatly reduced in both sexes after about 7 days of optimum food. Even starvation at that time will not stimulate an increase in long-flight behavior. It would appear that some type of physiological committment to reproduction which excludes or greatly reduces the tendency to migrate is made at that time. Photoperiod has little effect on migratory behavior when food is poor. But under optimal feeding conditions, short photoperiod enhances long flight behavior even among reproductive females. It would appear that migration to the aestivo-hibernation sites is accomplished primarily by newly emerged (pre-reproductive female) beetles. Strong selection pressure has apparently favored migration away from the aggregation sites in the early spring (short photoperiods) whether or not aphid prey are available, while migration during the summer (long photoperiod) is much more facultative, depending primarily on food abundance.