DISPOSITION AND FATE OF CUCURBITACIN-B IN 5 SPECIES OF DIABROTICITES

Five species of diabroticities with diffrent host-plant preferences produced an essentially identical array of metabolites when fed radiolabeled cucurbitacin B synthesized in vivo and purified from Cucurbita maxima Duchesne seedlings. All species excreted the bulk of the cucurbitacin (67.17-94.59% total dpm), permanently sequestered a small proportion of a cucurbitacin conjugate in the hemolymph (0.98-2.76%), and apportioned the remainder between the gut, the body, and the eggs (when present). Markedly different ratios between the excretory metabolites (i.e., polar vs. unmetabolized cuc) suggest that Dibrotica virgifera virgifera, a grass specialist, and Acalymma vittatum, a cucurbit specialist, have lower rates of metabolic alteration than the polyphagous D. undecimpunctata howardi, D. balteata, and D. cristata, which is associated with relict prairies. Mean life-spans of D. balteata and D. v. virgifera and male A. vittatum decreased significantly with continuous feeding on Cucurbita fruit containing cucurbitacins (vs. fruit devoid of cucs). The longevity of female A. vittatum, however, was unaffected by the presence of cucurbitacins.