Screening of Beauveria bassiana (Bals.) (Hypocreales: Cordycipitaceae) strains against Megalurothrips usitatus (Bagnall) (Thysanoptera: Thripidae) and conditions for large-scale production

Abstract

Background: Beauveria bassiana (Bals.) (Hypocreales: Cordycipitaceae) is an entomopathogenic fungus that has potential as a biological control agent against many insect pests. This study was conducted to optimize the conditions for large-scale production on rice of B. bassiana and evaluate its virulence against the bean flower thrips Megalurothrips usitatus (Bagnall) (Thysanoptera: Thripidae). Results: The optimal substrate quantity for conidia production was 200 g of rice per container (2.1 l), with substrate having a 52% moisture content, being supplemented with 2% cooking oil. In stage production of a batch, 150 ml of conidia suspension (at 24.33 × 107 spores/ml) was incubated for 10 days in SDA liquid medium amended with 4% glucose and 1.5% yeast extract. The SDA medium was then used to inoculate one container of the rice substrate. The optimum ratio of conidial suspension to substrate (v/v) was 20–25%. Virulence of the spore powder harvested from the rice substrate was same as that of produced on the SDA solid media against thrips. The level of control from an application of spore powder of the thrips M. usitatus was similar to that from chemical the pesticide spinetoram when applied in a cowpea (Vigna sinensis Endl) field. Conclusions: The optimized rice substrate system can be used for a large-scale production of B. bassiana spores, which can be used for field control of thrips.