Cucurbitacins are extremely bitter tetracyclic triterpenoids that are toxic to most organisms. Acalymma vittatum is stenophagous, subsisting almost entirely on plants in the Cucurbitaceae, which generally contain cucurbitacins. As for other diabroticite beetles, cucurbitacins are sequestered by A. vittatum and have been shown to act as phagostimulants and arrestants. However, we have found that sensitivity to cucurbitacin diminishes with continued sequestration. Colony A. vittatum were fed only roots and foliage of either Marketmore 76 (which contains a normal amount of cucurbitacin) or Marketmore 80 (a near isogenic line that contains no cucurbitacin) cucumber. Over 1200 individual beetles from the day of adult emergence to 15 days following emergence were placed in choice and no-choice arenas containing potted cotyledons of the two cucumber varieties for 24 hours. In choice tests, degree of preference was significantly influenced by both age and dietary history. In no-choice tests, age, sex, dietary history, and interactions among these variables all significantly affected the feeding response to cucurbitacin. For beetles on the cucurbitacin diet, over time, total foliage consumption of the cucurbitacin-containing cultivar declined to equal that of the cucurbitacin-free cultivar. These effects were also confirmed for feral A. vittatum. Ecological and applied implications of the reduction in sensitivity to cucurbitacin are discussed.
Species 1: Coleoptera Chrysomelidae Acalymma vittatum (striped cucumber beetle)
Keywords: Cucumis sativus, phagostimulant
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