Evaluating a dual microbial agent biopesticide with Bacillus thuringiensis var. kurstaki and Beauveria bassiana blastospores

Authors: SAYED, ATEF - Plant Protection Research Institute; Behle, Robert

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2017
Publication Date: 3/21/2017
Citation: Sayed, A.M., Behle, R.W. 2017. Evaluating a dual microbial agent biopesticide with Bacillus thuringiensis var. kurstaki and Beauveria bassiana blastospores. Biocontrol Science and Technology. 27(4):461-474. doi: 10.1080/09583157.2017.1303662.

Interpretive Summary: This research demonstrated the benefits of combining two insect pathogenic microbes (Bacillus thuringiensis and Beauveria bassiana) into a single biological pest control product when utilizing blastospores produced by economical fermentation as the source of the fungus rather than traditionally used conidial spores produced by more expensive solid substrate production techniques. The product with combined microbes had equal or better insecticidal activity than either pathogen used alone. Additionally, a variety of formulations with combined microbes were successfully prepared using pilot scale spray drying techniques. These initial laboratory successes will be evaluated under field conditions for a wide variety of insect pests to support development of this concept into a cost effective pest control product for general use as an environmentally friendly insecticide.

Technical Abstract: A biopesticide with a mixture of entomopathogenic microbial agents was studied for improvements in efficacy. Recently developed liquid fermentation techniques were used to produce blastospores of Beauveria bassiana (Balsamo) Vuillemin strain GHA (Bb), which were mixed with traditional fermentation of Bacillus thuringiensis Berliner kurstaki (Bt) spores and crystals. Based on a dosage response bioassay using Trichoplusia ni (Hübner) neonates exposed to treated leaf disks, the LC50 values were determined to be 3.85 x 10**7 spores mL**-1 for the unformulated Bt and 3.58 × 10**7 blastospores mL**-1 for the unformulated Bb. Using the same bioassay conditions, mixtures of Bt:Bb at ratios of 1:0, 0.75:0.25. 0.5:0.5, 0.25:0.75, and 0:1 indicated that the greatest mortality was caused by the 0.5:0.5 mixture ratio of the microbial agents. Based on these results, the 0.5:0.5 mixture was formulated as a dry powder by spray drying and applied to field-grown cabbage for comparison with commercial Bt and Bb products. Overall, the mixed agent treatment caused equal or greater mortality of exposed insects when compared with commercial products. The insecticidal interaction was determined to be synergistic when combining these two microbial agents into a single product, providing greater mortality of target insects. Assuming similar fermentation costs, the combined treatment could provide improved efficacy without increasing production costs. These benefits support the concept of formulating mixed microbial agents as an environmentally friendly pest control tool.