Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/25/1998
Publication Date: N/A
Interpretive Summary: Toxins produced by fungi in corn cause hundreds of millions of dollars of direct and indirect losses. Understanding how the fungi are spread to corn can suggest means for controlling them. A survey of corn at harvest in Mexico indicated high levels of sap beetles, which were the most abundant insect present. Incidence in corn of the fungus that makes aflatoxin, one of the most potent carcinogens known, was associated with sap beetle presence. Strategies directed toward control of fungal toxins in corn through control of insects that damage or carry the fungi should thus include sap beetles in addition to other insects commonly associated with fungal toxins in corn, such as caterpillars.
Technical Abstract: Field experiments were conducted from 1993 to 1997 in northern Tamaulipas, Mexico, to identify the sap beetles and other microcoleopterans attracted to maize ears, and to evaluate their abundance in relationship to growing season (spring or fall), ear wounding (caterpillars, birds, and artificial), crop phenology, cultivars, and aflatoxin contamination. Three species comprised 97% of the total captures: Carpophilus freemani, Cathartus quadricollis, and Sitophilus zeamais. Carpophilus freemani was by far the predominant species, comprising nearly 90% of all collections. Overall, compared to undamaged ears, microcoleopterans were 2-5 fold more abundant in caterpillar-damaged ears, and 5-28 fold more abundant in bird-damaged and artificially damaged ears. C. freemani seemed to respond more to ear wounding, (5-10 fold) than C. quadricollis and S. zeamais (2-4 fold). A maximum average density of 57 sap beetles per ear was observed in artificially damaged ears during the spring of 1993. Maximum abundance of microcoleopterans occurred from dough-hard to 25% kernel moisture stages. Carpophilis freemanii was abundant during all maize reproductive stages, whereas C. quadricollis and S. zeamais were only common when kernels were drying down (15-20% moisture). Number of sap beetles varied significantly among cultivars in both undamaged and damaged ears. Infection by Aspergillus flavus and aflatoxin contamination of maize was enhanced by ear wounding and incidence of sap beetles.