Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 11, 2002
Publication Date: N/A
Interpretive Summary: Bacillus thuringiensis is a bacterium that can be used as an alternative to chemical insecticides to control the European corn borer. Bacillus thuringiensis is not toxic to humans, and a corn field can be entered immediately following treatment. Therefore, B. thuringiensis remaining on the plant, live larvae on the plant, and insecticidal activity can be measured over time. Bacillus thuringiensis treatment resulted in 63 and 62% reductions in the number of live larvae and centimeters of tunneling between the control treated plots, respectively. The number of bacterial propagules collected and the amount of larval mortality decreased over time. The number of live larvae in the plant also served as a reliable indicator of the total amount of damage that these larvae would be expected to cause. Use of this technique to evaluate overall microbial insecticide effectiveness is less time consuming than traditional stalk splitting. This research will assist entomologists and crop scouts in evaluating effectiveness of B. thuringiensis to manage European corn borer.
Technical Abstract: Bacillus thuringiensis Berliner (Dipel ES) was applied to corn plants at 6.6 10**9, and 8.7 10**9 International Units (IU)/ha. Plants were infested with Ostrinia nubilalis Hubner (Lepidoptera: Crambidae) larvae on the same day as B. thuringiensis application as well as 1, 2, 4, 8, and 12 d after application. Evaluations were made to determine the number of live elarvae in the whorl of the plant, number of B. thuringiensis spores in the whorl of the plant, larval mortality from B. thuringiensis spores taken from the whorl of the plant, and the centimeters of tunneling in the stalk 40 d after larval infestation. Bacillus thuringiensis treatment resulted in 63 and 62% reductions in the number of live larvae and centimeters of tunneling between the control and mean of the two B. thuringiensis applications, respectively. The mean number of live larvae in the whorl 5 d following infestation was a reliable indicator of centimeters of tunneling that could be expected at 40 d (R**2 = 0.75; y = 0.54x + 5.02). The loss of insecticidal activity over time indicated a decrease in larval mortality in the bioassay and the increased numbers of live larvae recorded in the plant whorl.