Submitted to: Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 7, 1998
Publication Date: N/A
Interpretive Summary: Interpretive Summary. New strains and formulations of Bacillus thuringiensis are providing opportunities to expand the use of this highly desirable biological control agent. However, quantitative measurements of key variables that influence the efficacy of different products are needed to select the most appropriate product for a specific use. Therefore, studies were conducted to compare selected granular formulations containing different strains of B. thuringiensis for their effects on the European corn borer and to measure the effects of a nutrient-based feeding stimulant used with spray applications of B. thuringiensis on degradation by ultraviolet light. Results indicated that genetically modified B. thuringiensis, particularly where the B. thuringiensis toxin is produced without spores, are inferior to products containing spores. Therefore, when selecting a B. thuringiensis strain, the role of spores in relation to the amount of toxin present must be considered. Also, demonstration that nutrient-based feeding stimulants significantly protect B. thuringiensis on plants from ultraviolet light provides a basis for expanding the use of feeding stimulants. Thus, the combined studies on strains and environmental degradation provides information that will make possible the selection of preferred strains for specific uses and the development of more efficient use patterns for B. thuringiensis.
Five commercial granular formulations based upon Bacillus thuringiensis (Berliner) and marketed for controlling the European corn borer,Ostrinia nubilalis (H¿bner), were compared for potency using treated discs of bean leaves. Three formulations were similar both in terms of mortality and speed of kill. A formulation containing a strain of Bt developed by plasmid fusion caused mortality similar to the other three formulations but the speed of kill was slower. A fifth formulation containing a B. thuringiensis toxin produced by Pseudomonas flourescens Migula as result of a gene transfer caused substantially less mortality than any of the other formulations. An experimental water dispersable formulation, based on a previously developed granular matrix formulation containing Bt and a nutrient-based phagostimulant, was developed which caused significantly higher mortality of the European corn borer than a similar formulation without the phagostimulant. Simulated field studies were conducted to quantify the effects of the phagostimulant on feeding and potential protection of Bt from ultraviolet (UV) light. Bean plants treated with B. thuringiensis and the phagostimulant were exposed to different UV regimes under canopies made of specialized acrylic plastics and then infested with larvae of the corn earworm, Heliothis zea (Boddie). A significant interaction between the UV regimes and the phagostimulant was found, indicating that the phagostimulant acted both as a feeding stimulant and as a UV protectant to enhance the activity of B. thuringiensis.