Larvae ofFrumenta nundinellaZeller utilize two different resources of their only host, horsenettle (Solanum carolinenseL.). Larvae develop either within capsules fused from terminal leaves, or within fruits. In greenhouse rearing, the sex ratio at emergence was 1:1 for each type of development. Emergence from infested fruits required 50% more degree-days than emergence from leaf capsules. Fruit infestation occurred in the absence of pollination, demonstrating that moth larvae could stimulate parthenocarpy. Parthenocarpy also was induced by flower style removal, suggesting that tissue destruction by feeding larvae was sufficient to initiate fruit set. Stimulative parthenocarpy, which also occurs in fig wasps, ensures development of infested fruits.