Physical and Biological Prerequisites for Flight Activity in the Alfalfa Weevil, Hypera postica (Coleoptera: Curculionidae)1

Abstract

Adult alfalfa weevils, Hypera postica (Gyllenhal), may exhibit two periods of flight activity during their life cycle. Prediapause flights occur only after newly emerged adults have fed for at least 4 or 5 days, and usually begin in late afternoon or early evening, when air temperatures are above 20°C and light intensity is low or decreasing. These flights are not a direct response to changes in the environment, although unfavorable conditions may accelerate the dispersal process. Postdiapause flights, however, usually occur when weevils do not have an adequate food supply, but still retain sufficient energy reserves for sustained flight activity. Without appropriate tactile or gustatory cues from their host plant, weevils begin to migrate within 24 h. These flights probably occur near midday, because warm temperatures and intense illumination stimulate the greatest flight activity.