Ovicidal, larvicidal and insecticidal activity of strains of Beauveria bassiana (Balsamo) Vuillemin against the cigarette beetle, Lasioderma serricorne Fabricius (Coleoptera: Anobiidae), on rice grain

Abstract

Seven strains of Beauveria bassiana were evaluated for their effects on the eggs of Lasioderma serricorne under laboratory conditions. Strains were applied at a single dose of 0.03 g conidia kg−1 of grain = 2 × 109 conidia g−1 of kaolin kg−1 of grain. All strains were pathogenic on the eggs of L. serricorne. Two strains, MS-8, and 7284, caused the highest levels of egg mortality. These two strains were then formulated at a fixed dose of 0.03 g conidia, with kaolin as an active carrier, at doses of 0.0, 0.5 g, 1 g, 2 g and 3 g of kaolin kg−1 of grain. These powder formulations were evaluated for their effects on adult mortality, larval mortality, number of adults emerged, level of grain damaged and level of weight loss on rice grains. The highest levels of adult mortality and larval mortality were caused by Strain MS-8 at a kaolin dose of 3 g kg−1. It also caused the lowest levels of adult emerged (10%), grain damaged (1.07%) and weight loss (0.55%). When unformulated, the same dose of conidia performed poorly for the same parameters (64%; 20.2%; 3.37%). The highest levels of grain damaged (27%) and weight loss (6.04%) were observed in the untreated control (UTC). Observations made with a scanning electron microscope (SEM) showed that unformulated conidia clumped together whereas conidia formulated in kaolin remained as discrete conidia.