MORTALITY OF OVERWINTERING EGGS AND LARVAE OF THE ALFALFA WEEVIL IN OKLAHOMA

The alfalfa weevil, Hypera postica (Gyllenhal), is a univoltine specie s whose primary period of oviposition is during fall and winter in Okl ahoma, with hatching typically occuring in late winter and spring. The objectives of this study were to estimate the total number of eggs la id per generation by the alfalfa weevil, the mortality of eggs through the winter, and reductions in numbers of newly hatched larvae resulti ng from lethal low temperatures. The study was conducted in alfalfa fi elds located at Stillwater (northern) and Chickasha (southern), OK, fr om 1980 to 1990. Population densities of eggs and larvae of the weevil were determined at regular intervals from October to May for each gen eration. Subsamples of eggs were reared for viability estimates. A sum mation procedure was used to calculate total eggs laid per generation. Mean total egg production per generation exceeded 900 per 0.1 m2 at e ach location. Mortality of eggs averaged about 30% resulting from low temperatures (< -15-degrees-C). In most years, hatching began before t he last occurrence of temperatures below -6-degrees-C. These temperatu res killed most alfalfa top growth and most larvae that were present. Combined mortality of eggs and larvae hatching during winter resulted in an average reduction of 38% in the reproductive potential for the w eevil.