Mexican diabroticite beetles: II. test for preference of cucurbit hosts by Acalymma and Diabrotica spp.

Field collected adult diabroticites were three Cucurbita spp. in various combinations. Three Acalymma and five Diabrotica (Chrysomelidae: Luperini) species were tested in feeding choice and no-choice assays for their preference for bitter (cucurbitacin-containing) over non-bitter (without cucurbitacins) cucurbits, and for one of the two primary types of cucurbitacins. Tests were conducted in petri dishes and cages using plants in the cotyledon stage. All species significantly preferred the bitter over the non-bitter cucurbits (C. pepo L. var. Crookneck) in the tests offering a choice between cucurbitacin B-containing plants (C. pepo L. var. Ambassador) and no cucurbitacin-containing plants. Six species significantly preferred cucurbitacin E-containing plants (C. Martinezii L. Bailey) over no cucurbitacin-containing plants. Cucurbitacin B-containing plants were significantly preferred over cucurbitacin E-containing plants. The previously observed preferences in choice tests no longer occurred in no-choice tests. In cage experiments, beetles did not show preferences for a certain cucurbit host. These observations are interpreted with regard to the kairomonal function of cucurbitacins for diabroticite beetles and the hypothesized evolutionary association between diabroticites and Cucurbitaceae.