Submitted to: Journal of Entomological Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 5, 1998
Publication Date: N/A
Interpretive Summary: A bitter mutant of Hawkesbury watermelon, Citrullus vulgaris Schrad, is known to elicit a powerful feeding stimulant/arrestant effect on the corn rootworm. The bitter principal responsible for this effect in C. vulgaris is cucurbitacin-E glycoside. While this compound has been reported to be the principal cucurbiticin (more than 20 are known) in C. vulgaris, methods sused by those invesigators to substantiate its presence lacked thorough scientific rigor. In this study, we isolated the principal active in C. vulgaris and unambiguously confirmed its structure by mass spectrometry and nuclear magnetic resonance spectroscopy. Cucurbitacins and cucurbit plants containing cucurbiticins have been the focus of research in the last decade to exploit ways to utilize them in baits laced with toxicants to control corn rootworms. C. vulgaris offers considerable promise since it can be readily and cheaply cultivated in temperate climates for this purpose. Information provided in this study will assist scientists and pest management specialists in regulatory agencies that may wish to consider C. vulgaris as a potential resource for cucurbitacin-derived toxicant baits for control of corn rootworms.
Technical Abstract: Fractions obtained by open-column flash chromatography of a crude methanolic 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 component(s) that elicit a visitation/feeding stimulancy response to the southern 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 ionization mass spectrometry and proton nuclear magnetic resonance spectrometry to be cucurbitacin-E glycoside. Two other cucubitacin-like compounds were isolated and structures for them postulated. A procedure to prepare a crude, biologically active, extract of C. vulgaris is reported. Dose response data for the crude extract in laboratory tests against two diabroticite beetles, D. undecimpunctata howardi and D. virgifera virgifera LeConte, are also reported.