In a 2-year study, fruits from 21 plant types of 15 species from 6 genera (Citrullus, Cucumis, Cucurbita, Lagenaria, Luffa, andMomordica) of Cucurbitaceae were exposed to a natural population ofDiabrotica undecimpunctata howardiBarber to determine relative attractance of thc fruits to that insect. Analysis of cucurbitacins and their glycosides in the fruits revealed a positive correlation between their concentration and the number of spotted cucumber beetles attracted by the various plant species. This correlation dcmonstrated the attraction properties of low concentration (0.0–0.56 mg/g) of curcurbitacins and their glycosides.Cucurbita foetidissimaH. B. K.andCucumis dipsaceusEhrenb., the 2 most attractive species, were high in cucurbitacin concentration. The technique of exposing fruits toD. undecimpunctata howardihas potential as a bioassay to screen cucurbitacins in the fruits of other species. Attractant cucurbitacins can be useful in population assessment and in luring the beetle to an insecticide or to an adhesive.