In vitro analysis of DIMBOA catabolism in the Asian corn borer <Emphasis Type="Italic">Ostrinia furnacalis</Emphasis> (Lepidoptera: Crambidae)

Larvae of the Asian corn borer Ostrinia furnacalis (Guenée) must cope with 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a major toxic allelochemical present in its host plant, maize Zea mays L. UDP-glucosyltransferase (UGT), which conjugates glucose to various lipophilic toxic compounds and thereby makes them more hydrophilic for easier excretion, has been suggested to be involved in the detoxification of DIMBOA in several insects. Our previous in vitro assays using O. furnacalis midgut homogenates demonstrated that DIMBOA was catabolized only when UDP-glucose, a glucose donor for UGT activity, was included in the reaction mixture; however, DIMBOA glucoside, the expected product of UGT activity, was only detected in trace amounts in assay products. The present study revealed that DIMBOA glucoside was produced, but was immediately degraded by unidentified enzymes in the midgut homogenate that do not require UDP-glucose for their activities, suggesting the presence of a novel route for DIMBOA catabolism in O. furnacalis.