Sequestered Cucurbitacins and Pathogenicity of Metarhizium anisopliae (Moniliales: Moniliaceae) on Spotted Cucumber Beetle Eggs and Larvae (Coleoptera: Chrysomelidae)

Abstract

It has long been hypothesized that many luperine cucumber beetles ultimately consume and sequester highly bitter cucurbitacin triterpenes to gain protection from predators and possibly parasitoids. Here we expand this protection hypothesis to include antibiotic protection against entomopathogens. Specifically, we examine the ability of cucurbitacins sequestered in the eggs and larvae of Diabrotica undecimpunctata howardi Barber, the spotted cucumber beetle, to reduce the pathogenicity of the entomopathogen Metarhizium anisopliae . Bitter and nonbitter eggs and larvae (those with and without sequestered cucurbitacin glycosides) were exposed to 0,10 3 ,10 5 , and 10 7M. anisopliae conidia per milliliter of distilled water. A significantly greater percentage of both eggs and larvae containing cucurbitacins survived exposure to the fungus, suggesting that the adaptive value of cucurbitacin pharmacophagy in cucumber beetles includes an antibiotic benefit.