REPRODUCTIVE RESPONSES OF APHIDOPHAGOUS LADY BEETLES (COLEOPTERA, COCCINELLIDAE) TO NONAPHID DIETS - AN EXAMPLE FROM ALFALFA

Aphidophagous lady beetles feed on a variety of pre! in addition to pr eferred aphids. These alternative feuds ma!: serve only to maintain th e predator but do not permit immature growth or adult reproduction. We tested whether larvae of the alfalfa weevil, Hypera postica (Gyllenha l), are alternative foods for adults of 2 species of lady beetles, Coc cinella septempunctata L. and G. transversoguttata Brown, that breed i n alfalfa while feeding on the larvae as well as aphids. When collecte d fi-om alfalfa fields and placed on diets of weevils only, adults of both species generally gained weight. However. in contrast to females fed pen aphids, Acyrthosiphon pisum (Harris),females fed weevils produ ced very few eggs, almost all of which were laid in the first few days after the predators were placed on the weevil diet. When dissected. f emales fed weevils li:td only very small (previtellogenic) eggs in the ir ovaries. Similarly, females produced very few eggs, and held only p revitellogenic eggs of very small size in their ovaries, when provided only sucrose (dissolved in water in 15% solution). When provided both weevils and sucrose, however, females of both species laid eggs in mo dest numbers. These results indicate that weevil larvae serve as alter native foods for the lady beetles, and that reproduction nevertheless can occur in the absence of preferred aphid prey when weevil larvae ar e combined ill the diet with sucrose, another alternative food. Becaus e nectar carl serve as a natural source of sucrose in or near,alfalfa fields, some reproduction by lady beetles may occur in fields infested with weevil larvae even in the absence or low abundance of aphids.