Alfalfa Weevil (Coleoptera: Curculionidae) Phenology with its Host Crop and Parasitoids in Virginia

Abstract

Alfalfa weevil, Hypera postica (Gyllenhal), phenology is influenced by winter climate. In 1997 we initiated a 2-yr study of alfalfa weevil phenology with respect to its host crop and parasitoids in three geographically distinct locations of Virginia: the central Piedmont, Shenandoah Valley, and southwestern region. Alfalfa weevil populations from nine fields were sampled regularly from November until first harvest in each season. Eggs laid in December and January resulted in alfalfa weevil larval infestations in March and April at all locations. Because of warmer winter temperatures, eggs developed faster in the Piedmont compared with the higher elevations, and resulted in larval populations attacking alfalfa earlier in the season, when the crop was at an earlier growth stage. The adult parasitoid, Microctonus aethiopoides Loan, was synchronized poorly with alfalfa weevil populations in Virginia. At all locations studied, adult emergence of first generation M. aethiopoides occurred in April and early May, when few overwintering alfalfa weevil adults were present in fields. Emergence of the second generation of the parasitoid occurred in late May to June after many of the fields had been harvested. The larval parasitoid, Bathyplectes anurus (Thomson), was well synchronized with its host in Virginia. The activity period of the parasitoid overlapped the peak occurrence of alfalfa weevil larvae at all locations.