SPECTRAL CHARACTERIZATION OF CUCURBITACINS IN A BITTER MUTANT OF HAWKESBURY WATERMELON (CITRULLUS-VULGARIS SCHRAD) THAT ELICIT A FEEDING RESPONSE TO DIABROTICITE BEETLES (COLEOPTERA, CHRYSOMELIDAE)

Fractions obtained by open-column flash chromatography of a crude meth anolic extract of the rind of a bitter mutant of Hawkesbury watermelon , Citrullus vulgaris Schrad, were further purified by preparative high -performance liquid chromatography (HPLC) to isolate chemical componen t(s) that elicit a visitation/feeding stimulancy response to the south ern corn rootworm, Diabrotica undecimpunctata howardi Barber. Activity of chromatographic fractions were followed with a laboratory bioassay involving total insect-response counts. The chemical structure of the most active component in C. vulgaris was confirmed by chemical ioniza tion mass spectrometry and proton nuclear magnetic resonance spectrosc opy to be cucurbitacin-E glycoside. Two other cucurbitacin-like compou nds were isolated and structures for them postulated. A procedure to p repare a crude, biologically active, extract of C. vulgaris is reporte d. Dose-response data for the crude extract in laboratory tests agains t two diabroticite beetles D. undecimpunctata howardi and D. virgifera virgifera LeConte are also reported.