EFFECTS OF MAIZE WEEVILS (COLEOPTERA, CURCULIONIDAE) ON PRODUCTION OF AFLATOXIN B-1 BY ASPERGILLUS-FLAVUS IN STORED CORN

Insects play an important role as facilitators of the aflatoxin-producing fungus, Aspergillus flavus Link, in both preharvest and postharvest corn. The current study investigated the role of maize weevils, Sitophilus zeamais Motschulsky in enhancing aflatoxin nl content in stored corn. In laboratory experiments, aflatoxin B-1 was quantified with all indirect enzyme-linked immunosorbent assay (ELISA) on corn following artificial infestation with adult weevils that had each been topically treated with 100 spores of A. flavus. Corn kernels infested with A. flavus-contaminated weevils had significantly higher levels of aflatoxin B-1 than A. flavus-inoculated corn without weevils. The presence of maize weevils resulted in increased kernel moisture content during incubation, and grain moisture was positively correlated with aflatoxin content across treatments receiving spores. Aflatoxin B-1 levels were higher in corn treated with fungus-contaminated weevils compared with corn that Mras mechanically damaged and inoculated with spores, which in turn had more aflatoxin than undamaged corn treated with spores. Aflatoxin B-1 content in corn increased with time of weevil exposure from 7 to 21 d, but decreased after 28 d of exposure. Aflatoxin levels in infested corn increased significantly with increased numbers of A. flavus-contaminated weevils. Maize weevils carried spores both internally and externally; however, substantial numbers of spores were intimately associated with the exoskeleton of adult weevils. These findings indicate that maize weevils facilitate the growth of A. flavus and aflatoxin production in corn by increasing surface area susceptible to fungal infection and increasing moisture content as a result of weevil metabolic activity. Weevil activity can have a profound effect on postharvest aflatoxin production even though little initial inoculum is present.