MULTIVARIATE METHOD FOR TEMPORAL PREDICTIONS OF ALFALFA WEEVIL LARVALPOPULATIONS EXCEEDING THE ECONOMIC THRESHOLD IN OKLAHOMA

Absolute density sampling was conducted to determine population densit ies of Hypera postica (Gyllenhal) eggs and larvae at two locations in central Oklahoma from 1971 to 1990. For each generation of the weevil, egg deposition began following the return of adults from summer estiv ation sites during October and November and continued until the follow ing April. Although hatching began as early as December, the appearanc e of large numbers of larvae coincided with growth of the first alfalf a crop from February to May. Depending upon effects of weather conditi ons on egg development and survival, the time when larval numbers firs t exceeded the economic threshold ranged from late February to April. Multivariate discriminant analysis with five variables related to weev il egg numbers and temperature conditions was used in deriving a model for predicting by 15 February whether the economic threshold would be exceeded in late February, early March (1-15), late March (16-31), or April. When tested, >90% of the predictions of the model were correct . This model will provide valuable assistance to growers and consultan ts in determining when field scouting should be conducted to make deci sions regarding sprays for alfalfa weevil control.