Effects of Alfalfa Dormancy on Egg and Larval Population Levels of the Alfalfa Weevil (Coleoptera: Curculionidae)

Abstract

Two studies were done between 1982 and 1985 to determine the effects of alfalfa dormancy on egg and larval population densities of the alfalfa weevil ( Hypera postica (Gyllenhal)). Dormancies of the alfalfa ( Medicago sativa L.) entries were estimated based on the amount of growth after the last harvest in September. As alfalfa dormancy was reduced, greater growth in late fall and early spring provided more favorable habitat and abundant ovipositional sites for weevil adults. Egg populations were estimated in January and March, and larval populations were sampled in March and April. Dormant alfalfa entries had significantly less fall growth than those rated as nondormant and had significantly lower egg numbers, as well. Egg population densities averaged 69.0 eggs/0.025 m2 in the most dormant and 117.5 eggs/0.025 m2 in the nondormant entries. Larval populations averaged 99.0 larvae/25 stems in the most dormant and 120.3 larvae/25 stems in the nondormant entries. Nondormant entries were usually more heavily infested by weevil larvae than their dormant counterparts.