Protection from stored grain insects using transgenic maize hybrids and implications for Aspergillus flavus and aflatoxin contamination

Authors: MANDAP, JULIE AIZA - Iowa State University; HELLMICH, RICHARD - Iowa State University; Busman, Mark; MAIER, DIRK - Iowa State University; MUNKVOLD, GARY - Iowa State University

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2024
Publication Date: 3/1/2024
Citation: Mandap, J.A.L., Hellmich, R.L., Busman, M., Maier, D.E., Munkvold, G.P. 2024. Protection from stored grain insects using transgenic maize hybrids and implications for Aspergillus flavus and aflatoxin contamination. Journal of Stored Products Research. 106. Article 102258. https://doi.org/10.1016/j.jspr.2024.102258.
DOI: https://doi.org/10.1016/j.jspr.2024.102258

Interpretive Summary: Genetically modified corn (Bt corn) is widely used by U.S. farmers to combat insect pests without relying on the application of chemicals. Bt corn provides control over insects that have historically had a large impact on growing corn in the field. Stored grain can also be affected by insects and fungi such as Aspergillus flavus that infest insect-damaged grain. Aspergillus flavus produces aflatoxin which harms human and animal consumers of the damaged grain. While control over insects has been demonstrated in the field, there have been few studies on the effects of Bt corn on insects, or fungi and toxins in insect damage corn, in harvested grain placed in storage. Therefore, a researcher in Peoria, Illinois, collaborated with scientists at the Iowa State University to study the effects of the Bt trait on control of two insects that are a problem in stored grain - Indian meal moth and maize weevil - and the storage fungus Aspergillus flavus. Bt and non-Bt corn were stored and infested with the insects alone or with insects and Aspergillus. There was no insect damage or grain weight loss in Bt corn, regardless of the presence or absence of the fungus. By the end of 28 days, insects were eliminated from the Bt corn and there was no increase in the contamination of the corn with aflatoxin from the fungus. In non-Bt grain, toxin levels increased by almost two-fold when insects were present. Insect infestation only increased toxin contamination in the absence of the Bt trait. This study demonstrated that the Bt trait can be effective against stored-grain insects and suggests that the use of Bt corn will also reduce the risk of A. flavus and aflatoxin contamination in stored corn.

Technical Abstract: Transgenic maize has been assessed thoroughly in the field but not in storage, particularly regarding the effects of lepidopteran and coleopteran Bt events on the interactions of stored-grain insects and storage fungi such as Aspergillus flavus. Indianmeal moth (Plodia interpunctella) and maize weevil (Sitophilus zeamais) are economically important stored-grain insect pests of maize. In this study, non-Bt and Bt maize hybrids were infested with Indianmeal moth larvae or maize weevil adults alone or in combination with conidia of A. flavus in storage at 32°C and 80-85% relative humidity. In Bt hybrids with lepidopteran events expressing Cry1Ab, Cry1Ab x Cry1F, and Cry1Ab x Cry1F x Vip3Aa proteins, the mortality of Indianmeal moth was 100% by the end of the 28-day storage period. In Bt hybrids with coleopteran events expressing mCry3A and mCry3A x Cry34A/35Ab1 proteins, mortality of maize weevil was 100%. On the non-Bt grain, aflatoxin levels increased by almost 2-fold in the presence of either Indianmeal moth or maize weevil. Insect infestation did not enhance A. flavus contamination or aflatoxin contamination on transgenic hybrids because of deterred insect activity. In the non-Bt hybrid, A. flavus caused increased mortality, reduced survivorship, and lower growth indices of both insects, limiting their feeding in the A. flavus coated conventional grain. As a result, insect damage and grain weight loss were significantly higher in the absence of A. flavus. In the transgenic hybrids, no insect damage and grain weight loss were observed regardless of the presence or absence of A. flavus. Insect infestation only enhanced aflatoxin contamination in the absence of Bt events. This study demonstrated that Bt proteins were effective against the stored-grain insects Indianmeal moth and maize weevil and suggests that the use of transgenic hybrids can mitigate the risk of A. flavus and aflatoxin contamination in stored grain.