title: Toxicity of aflatoxin B1 to Helicoverpa zea and bioactivation by cytochrome P450 monooxygenases.
abstract: Infestation of corn (Zea mays) by corn earworm (Helicoverpa zea) predisposes the plant to infection by Aspergillus fungi and concomitant contamination with the carcinogenic mycotoxin aflatoxin B1 (AFB1). Although effects of ingesting AFB1 are well documented in livestock and humans, the effects on insects that naturally encounter this mycotoxin are not as well defined. Toxicity of AFB1 to different stages of H. zea (first, third, and fifth instars) was evaluated with artificial diets containing varying concentrations. Although not acutely toxic at low concentrations (1-20 ng/g), AFB1 had significant chronic effects, including protracted development, increased mortality, decreased pupation rate, and reduced pupal weight. Sensitivity varied with developmental stage; whereas intermediate concentrations (200 ng/g) caused complete mortality in first instars, this same concentration had no detectable adverse effects on larvae encountering AFB1 in fifth instar. Fifth instars consuming AFB1 at higher concentrations (1 microg/g), however, displayed morphological deformities at pupation. That cytochrome P450 monooxygenases (P450s) are involved in the bioactivation of aflatoxin in this species is evidenced by the effects of piperonyl butoxide (PBO), a known P450 inhibitor, on toxicity; whereas no fourth instars pupated in the presence of 1 mug/g AFB1 in the diet, the presence of 0.1% PBO increased the pupation rate to 71.7%. Pupation rates of both fourth and fifth instars on diets containing 1 mug/g AFB1 also increased significantly in the presence of PBO. Effects of phenobarbital, a P450 inducer, on AFB1 toxicity were less dramatic than those of PBO. Collectively, these findings indicate that, as in many other vertebrates and invertebrates, toxicity of AFB1 to H. zea results from P450-mediated metabolic bioactivation.
authors.affiliation: Department of Entomology, University of Illinois, Urbana, 61801, USA. rszeng@life.uiuc.edu
authors.forename: Ren Sen
authors.initials: RS
authors.lastname: Zeng
authors.forename: Ren Sen L
authors.initials: RS
authors.lastname: Zeng
authors.forename: Guodong
authors.initials: G
authors.lastname: Niu
authors.forename: Zhimou
authors.initials: Z
authors.lastname: Wen
authors.forename: Mary A
authors.initials: MA
authors.lastname: Schuler
authors.forename: May R
authors.initials: MR
authors.lastname: Berenbaum
mesh_terms: D016604:Aflatoxin B1 / Q000633:toxicity*; D000818:Animals; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects* / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000633:toxicity; D008658:Inactivation, Metabolic; D007305:Insecticide Resistance; D007814:Larva / Q000187:drug effects; D007915:Lepidoptera / Q000187:drug effects* / Q000502:physiology; D010574:Pesticide Synergists / Q000633:toxicity; D010634:Phenobarbital / Q000494:pharmacology; D010882:Piperonyl Butoxide / Q000633:toxicity; D018675:Toxicity Tests
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D010574:Pesticide Synergists; D003577:Cytochrome P-450 Enzyme System; D016604:Aflatoxin B1; D010882:Piperonyl Butoxide; D010634:Phenobarbital