Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2005
Publication Date: 11/1/2005
Citation: Flinn, P.W., Kramer, K.J., Throne, J.E., Morgan, T.D. 2005. Protection of stored maize from insect pests using a two-component biological control method consisting of a hymenopteran parasitoid, Theocolax elegans, and transgenic avidin maize powder. Journal of Stored Products Research 42: 218-225. Interpretive Summary: Insects reduce the quality of stored grain and other stored products in the U.S. and in the world. It is estimated that losses due to insects are 5 to 10%, or about 1.25 to 2.5 billion dollars. We conducted laboratory studies to test the effectiveness of a combined treatment of transgenic avidin corn powder plus a small insect parasitoid to control both internal and external insect pests in stored corn. The avidin powder alone failed to suppress the internal insects, and the parasitoid alone did not control the external insect pests. However, the combined treatment suppressed both internal and external insect pests an average of 80% after 8 weeks. This study demonstrated that combining the avidin corn powder treatment with the insect parasitoid was much more effective in suppressing both internal and external insect pests than either treatment alone. This is the first study to compare the effectiveness of a combined treatment of transgenic avidin corn powder and a parasitoid insect to control a mixture of insect pests in stored corn. Information from this study should be of great interest to farmers and elevator managers, especially those interested in sustainable agricultural systems.
Technical Abstract: Biological control materials consisting of the hymenopteran parasitoid, Theocolax elegans (Westwood), and transgenic avidin maize (corn) powder were tested to determine if the individual or combination treatment would protect stored grain from infestation by both internal and external insect pests. Small-scale tests were conducted in plastic jars containing 3 kg of non-transgenic maize. We tested treatments of 0.3% powdered avidin maize, the parasitoid wasp, and the combination of the parasitoid plus 0.3% powdered avidin maize. One pair each of Sitophilus zeamais Motschulsky, Tribolium castaneum (Herbst), and Cryptolestes ferrugineus (Stephens) was added to each jar. After 8 weeks, the entire contents of each jar were examined for adult insects. Control and avidin maize powders had no detrimental effects on the beneficial insect parasitoid T. elegans. The parasitoid suppressed populations of the internal feeder S. zeamais. The avidin maize powder treatment had no effect on S. zeamais because these larvae developed inside the maize kernels where no avidin maize powder was present. For S. zeamais, the combination treatment was not significantly different from the parasitoid treatment. In contrast, populations of the external feeder T. castaneum were not suppressed by the parasitoid but were suppressed by the avidin maize powder treatment. There were no significant differences in population density of the external feeder C. ferrugineus in the control, avidin maize powder, and parasitoid treatments. However, C. ferrugineus density in the avidin maize powder-parasitoid combination treatment was significantly less than the control treatment. The total number of insects for all three species in the combination treatment was significantly less than the control or the parasitoid treatment but not the avidin maize powder treatment. The parasitoid-avidin combination treatment had the greatest percentage reduction for all three insect species and resulted in 78, 94, and 70% reductions in populations of S. zeamais, T. castaneum, and C. ferrugineus, respectively, when compared to the control treatment. The percentage reductions for the parasitoid treatment were 70, 8, and 20% for S. zeamais, T. castaneum, and C. ferrugineus, respectively. For the avidin maize powder treatment, populations of S. zeamais, T. castaneum, and C. ferrugineus were reduced by 10, 85, and 40%, respectively. The combination treatment of avidin maize powder plus the release of parasitoid wasps was superior to either treatment alone when applied to mixed populations of internal and external feeders. While avidin is fairly effective as an insecticide against the external feeders, it is ineffective against the internal feeder. By using parasitoids with an insecticidal powder that does not affect the efficacy of the parasitoids, stored grain managers would be assured of protection of commodities from both internally and externally feeding insects.