CUCURBITACINS AS FEEDING AND OVIPOSITION DETERRENTS TO INSECTS

Cucurbitacins, the bitter triterpenes common to all Cucurbitaceae, are thought to be potent feeding deterrents for all insects not adapted t o exploiting cucurbits. Yet appropriate choice tests not confounded by possible effects from phytochemical induction have only been conducte d on a few chrysomelid leaf beetle spp. To examine the extent to which cucurbitacins deter feeding across several taxa of mandibulate and ha ustellate insects, we conducted feeding preference tests, pitting host tissues exogenously coated with a methanol dilution of cucurbitacin B against tissues coated with only methanol. Four mandibulate herbivore s [Popillia japonica Newman, Cerotoma trifurcata (Forster) Leptinotars a decemlineata (Say) and Trichoplusia ni (Hubner)], 2 mandibulate detr itivores [Tenebrio molitor L. and Nauphoeta cinerea (Olivier)] and 3 h austellate herbivores [Gargaphia solani Heidemann, Corythucha ciliata (Say), Peregrinus maidis (Ashmead), and Acyrthosiphon pisum (Harris)] were examined. We also investigated the ability of cucurbitacin B to d eter Ostrinia nubilalis (Hubner) and Spodoptera exiqua (Hubner) female s from ovipositing on heated substrates. Two patterns emerged from our feeding assays: nonadapted insects with mandibulate mouthparts were d eterred from feeding on food tainted with cucurbitacins, whereas insec ts with haustellate mouthparts preferred cucurbitacin-treated food. Ov iposition assays with O. nubilalis and S. exiqua revealed significant deterrence at doses of 15 mu g cucurbitacin B per square centimeter. T he data suggest that cucurbitacins are generalized antifeedants for no n-adapted mandibulate insects but may actually be phagostimulants for phytophagous insects with haustellate mouthparts. We report on the ovi position deterrence for this class of compounds.