Toxicity of Bacillus sp. (Bacillales: Bacillaceae) on the fungus gnats, Bradysia aff. ocellaris larvae (Diptera: Sciaridae)

Abstract

Bacillus thuringiensis (Bt) Berliner has potential for use in insect management. Its use can be an alternative for the management of Bradysia aff. ocellaris (Comstock), considered one of the main strawberry pests in a soilless system. Therefore, the objective of this work was to evaluate the toxicity of different bacteria on B. aff. ocellaris in laboratory and greenhouse bioassays. The following isolates were used in the experiments: Bacillus circulans (Bc), B. thuringiensis var. oswaldo cruzi (Bto) or B. thuringiensis var. israelensis (Bti) and B. thuringiensis var. kurstaki (Btk) In the laboratory, B. aff. ocellaris larvae showed high susceptibility to Bti isolate (92 % mortality) 14 days after treatment exposure (DAET). In contrast, the isolates Bc, Bto, and Btk showed less than 32 % mortality, not differing from the control treatment (water – 22 % mortality). According to the concentration-response curves the values of lethal concentration LC50 and LC90 were 4 x 106 CFU.mL-1 and 4 x 1015 CFU.mL-1. By applying Bti (4 × 1012 CFU.mL-1) at the base of strawberry plants growing in plastic pots containing commercial plant substrate, a reduction of 26 % in the emergence of B. aff. ocellaris was observed. According to these results, the Bti isolate is considered promising for the formulation of bioinsecticides based on Bt for the management of B. aff. ocellaris in strawberry culture.