Diatomaceous earth and Beauveria bassiana in polyvinyl alcohol matrices, a combined effect for Pieris brassicae control

Abstract Cabbage larvae (Pieris brassicae, Lepidoptera: Pieridae) are an important pest in organic farming; therefore, biological pest control alternatives are being sought. The effect of Beauveria bassiana (Bb) combined with diatomaceous earth (DE) in a polyvinyl alcohol flask (Bbl), as well as the combination between them (Bb+DE, BbI+DE) on P. brassicae and Galleria mellonella larvae inoculated by aspersion or immersion was evaluated. Prior to the experiment, the viability of B. bassiana was assessed and one of three commercial brands of diatomaceous earth was selected based on the shape and damage caused to G. mellonella. Radial shapes with and without edges were more common in the diatomaceous earth types, but these did not define efficacy on cuticle damage. The result showed that the Bb+DE treatment had greater damage, followed by the Bbl+DE treatment applied by aspersion. The highest mortality in G.mellonella was 70.1 % with Bb at 120 h after sprinkled, while in P. brassicae, mortality reached 42.1 % with Bbl+DE; thus, it is important to highlight the importance of the inoculation method and larvae types used when effectiveness bio-trials are performed.