Abstract
We compared three formulations of B. thuringiensis var. kurstaki (Btk) for their insecticidal activity against first-instar OLR. Products tested included: (1) NOVO Laboratories Biobit, a flowable concentrate containing live bacteria with spores and parasporal crystal protein bodies; (2) Abbott Laboratories Dipel 2X, a wettable powder also containing active bacteria with spores and parasporal crystal protein bodies; and (3) Mycogen Corporations MVP Bioinsecticide, a flowable concentrate containing dead bacterial cells which bioencapsulate the Btk proteins. The AI in each of these products is the insecticidal protein, or delta-endotoxin, of Btk. Dose-response was determined by feeding trials exposing first-instar OLR to each product. Serial dilutions of each formulation were made and 10 μ1 of each dilution was applied to the surface of an agar-based diet (Bioserv No. 9370) and then allowed to air dry. One larva was placed in each vial containing ca. 1 ml of surface-contaminated diet (surface area = 1 cm2). Thirty to 60 larvae were observed for each dilution and formulation tested. Doses were expressed in mg AI per sq. cm. Mortality evaluations were made after 3, 5, and 7 days. Response data were analyzed by the POLO-PC PROBIT procedure (LeOra Software, 1987).
Relationship of the syntheses of spore coat protein and parasporal crystal protein in Bacillus thuringiensis.
