The fungus Beauveria bassiana is being studied as a possible microbial insecticide against European corn borers in corn. Recent research in Iowa has demonstrated that foliar applications of one B. bassiana isolate (ARSEF 3113) provides season long suppression of corn borers due to the ability of the fungus to enter inside the corn stalk and move throughout the plant.
A question remains whether use of this fungus against corn borers would reduce the number of beneficial insects such as lady beetles. The twelvespotted lady beetle, Coleomegilla maculata, is a common predator of aphids and European corn borer eggs and small larvae on corn. Studies by Pingel and Lewis in Iowa evaluated the potential effects of the isolate ARSEF 3113 on C. maculata adults and larvae. One hundred forty fourth stage larvae were exposed to a granular formulation of B. bassiana spores for 24 hours, and then held for 3 weeks to test for infection. Last stage larval lady beetles were placed on corn plants in the field immediately after application of a granular formulation of the fungus, and then removed after one and two days. Larvae were returned to the laboratory and held for 3 weeks to test for infection. None died from the fungus nor could it be isolated from any of the larvae or adults. Although C. maculata is known to be susceptible to some isolates of B. bassiana, these studies suggest that the ARSEF 3113 isolate would be compatible with survival of C. maculata in corn. Other studies examined the seasonal occurrence of naturally occurring C. maculata and B. bassiana in leaf collar tissue of corn plants and in the soil. C. maculata numbers did not increase until late July or early August. Naturally occurring B. bassiana was not found in leaf collar tissue after July 9, but was found in the soil throughout the summer. This suggests that C. maculata may naturally avoid exposure to B. bassiana because it feeds above-ground on the plant surface at a time when the fungus is at low levels in external plant tissue.
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