The western corn rootworm (WCR),Diabrotica virgiferaLeConte, demonstrated strong affinities for aggregation and feeding on the foliage of certain wildCucurbitaspecies with relatively high concentrations of cucurbitacin “bitter principles.” Most preferred were xerophytic species of the Digitata group—C. digitataGray,C. cylindrataBailey andC. palmataWats. and mesophytic species of the Lundelliana group—C. lundellianaBailey,C. okeechobeensisBailey andC. ecuadorensisCutler and Whitaker. Xerophytic species were more susceptible to injury and seldom survived continuous 24-h exposure to natural infestations. The spotted cucumber beetle (SCB),D. undecimpunctata howardiBarber, exhibited similar aggregation and feeding responses to wild mesophyticCucurbitaspecies with high cucurbitacin foliage but showed a more consistent feeding preference for cultivated species than the WCR. Both species preferred fruits of feralC. texanaGray andC. andreanaNaud. with high cucurbitacin over non-bitter fruits of their cultivated relatives,C. pepoL. andC. maximaDuchesne, respectively. The combined plant and insect factors which interact to bring about the SCB-WCR/Cucurbitaassociations observed here are discussed.