The effect of different formulations of B eauveria bassiana on S itophilus zeamaisin stored maize

Abstract

Beauveria bassiana conidia were formulated as a dustable powder (DP), as oil suspensions (OS) and as a novel hydrogenated rapeseed oil pellet. These formulations were assessed against Sitophilus zeamais Motsch. to study their potential use in the control of stored grain pests. Conidial viability was maintained well in the fat pellet formulation (84.7% germination after 45 days storage at 25°C) and in the DP (83.3%), but less well in the OS formulation (55.3%). Twenty four hours of direct contact of S. zeamais with the fat pellet formulation containing 10 10 conidia/g gave 100% mortality after 7 days. Mineral oil and a mineral and maize oil mixture, without conidia, or as OS with B. bassiana at a concentration of 10 9 conidia/ml (both at 20 ml/kg grain) showed the highest level of control in maize grains; the oils alone were insecticidal and gave an oily appearance to the grain; there was a small but significant effect of adding B. bassiana to the mineral and maize oil mixture applied at 5 ml/kg of grain. There was no benefit of adding conidia with those treatments. The DP formulation achieved up to 90% control after 15 days at 25°C with an application of 20 g of DP per kg of maize (2×10 10 conidia/kg maize), and 77.5% with a dose of 5 g/kg (5×10 9 conidia/kg maize). The fat pellet formulation resulted in low levels of mortality (21–31%) when used in maize grains.