Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2009
Publication Date: 8/13/2009
Citation: Niu, G., Siegel, J.P., Schuler, M.A., Berenbaum, M.R. 2009. Comparative Toxicity of Mycotoxins to Navel Orangeworm (Amyelois transitella) and Corn Earworm (Helicoverpa zea). Journal of Chemical Ecology. 35(8):951-957. Interpretive Summary: Mycotoxins, such as aflatoxins and ochratoxins, are widely distributed in nature and are frequently problematic crop contaminants that cause millions of dollars of annual losses in the United States. Insect infestations of crops significantly exacerbate mycotoxin contamination. The sensitivity of two lepidopteran species, Amyelois transitella (navel orangeworm, NOW) and Helicoverpa zea (corn earworm) to two classes of mycotoxins (aflatoxins and ochratoxin) produced by fungi belonging to the genus Aspergillus were evaluated. Levels of Aflatoxin B1 are highly regulated in commodities, and this chemical is produced by fungi contaminating tree nuts, the host of A. transitella, and corn, the host of H. zea. The navel orangeworm was 100 times more tolerant to Aflatoxin B1 than was the corn earworm. The navel orangeworm was also more tolerant to Ochratoxin A than was the corn earworm. Although the navel orangeworm is considered to be a generalist because it develops an several nuts as well as figs, pomegranates and loquats, it appears to be specialized for survival on diets that are heavily contaminated with fungi and their toxic metabolites. It can survive on these mycotoxin-contaminated diets because it does not convert Aflatoxin B1 into its most toxic form. This research is significant because it suggests that navel orangeworm is closely associated with fungi and can possibly actively spread them into nuts. Furthermore, because the navel orangeworm possesses unique metabolic pathways, it may become quickly resistant to a wide range of new insecticides that are coming onto the market.
Technical Abstract: Mycotoxins, such as aflatoxins and ochratoxins, are widely distributed in nature and are frequently problematic crop contaminants that cause millions of dollars of annual losses in the United States. Insect infestations of crop plants significantly exacerbate mycotoxin contamination. Damage to a variety of nut species by Amyelois tranistella Walker(navel orangeworm, NOW)is associated with infection by Aspergillus species and comcomitant production of aflatoxins and ochratoxins. Resistance to aflatoxins in this lepidopteran is compared here with the levels of resistance in Helicoverpa zea (corn earworm, CEW) another lepidopteran that routinely encounters aflatoxins in its diet, albeit at lower levels. Measured as the developmental delay caused by aflatoxins B1 (AFB1) it is apparent that the LC50 for AFB1 is 100 times greater for A. transitella than for H. zea. Similarly, A. transitella first instars display substantially higher tolerance to ochratoxin A, another mycotoxin contaminant produced by Aspergillus species, than do H. zea first instar larvae. Amyelois transitella, although a host plant generalist, may well be highly specialized for mycotoxin detoxification.