In vitro metabolism of aflatoxin B₁ by larvae of navel orangeworm, Amyelois transitella (Walker) (insecta, lepidoptera, pyralidae) and codling moth, Cydia pomonella (L.) (insecta, lepidoptera, tortricidae)

Larvae of the navel orangeworm (NOW), Amyelois transitella (Walker), a major pest of almonds and pistachios, and the codling moth (CM), Cydia pomonella (L.), the principal pest of walnuts and pome fruits, are commonly found in tree nut kernels that can be contaminated with aflatoxin, a potent carcinogen. The ability of larvae of these insects to metabolize aflatoxin B₁ (AFB1) was examined. A field strain of NOW produced three AFB1 biotransformation products, chiefly aflatoxicol (AFL), and minor amounts of aflatoxin B_2a (AFB2a) and aflatoxin M₁ (AFM1). With AFL as a substrate, NOW larvae produced AFB1 and aflatoxicol M₁ (AFLM1). A lab strain of CM larvae produced no detectable levels of AFB1 biotransformation products in comparison to a field strain which produced trace amounts of only AFL. Neither NOW nor CM produced AFB₁-8,9-epoxide (AFBO), the principal carcinogenic metabolite of AFB1. In comparison, metabolism of AFB1 by chicken liver yielded mainly AFL, whereas mouse liver produced mostly AFM1 at a rate eightfold greater than AFL. Mouse liver also produced AFBO. The relatively high production of AFL by NOW compared to CM may reflect an adaptation to detoxify AFB1. NOW larvae frequently inhabit environments highly contaminated with fungi and, hence, aflatoxin. Only low amounts, if any, of this mycotoxin occur in the chief CM hosts, walnuts, and pome fruits. Characterizations of enzymes and co-factors involved in biotransformation of AFB1 are discussed. Published 2001 Wiley-Liss, Inc.