Insecticidal activity of filtrate of Beauveria bassiana cultures incubated under the temperatures of 25°C and 34 °c against larvae Spodoptera litura

Abstract

Beauveria bassiana has been widely used to control lepidopteran larvae, such as Spodoptera litura. The objective of this research was to observe the mortality and median Lethal Time (LT50) of larval S. litura after exposure of filtrate of B. bassiana cultures incubated under temperatures of 25° and 34°C. The isolates used were 10 isolates of B. bassiana and they were incubated under temperatures 25 and 34 °C in liquid media for 6 wk. The results showed that the highest mortality caused by B. bassiana was found on the fungus incubated under 25 °C and was significantly different from that of temperature 34 °C. The shortest LT50 of larval S. litura was found on the fungus incubated under temperature 25 °C and was significantly different from that of temperature 34 °C. The highest mortality was found on isolate BTmPc (96%) incubated under temperature 25 °C with the shortest LT50 (7.51 d), which was not significantly different from isolate BTmTr (93.33%) incubated under temperature 25°C with the LT50 (7.31 d). Therefore, isolate BTmTr incubated under temperature 25 °C was the most effective on killing S. litura larvae. However, isolate of BMkMs incubated under 34 °C was still caused the highest percentage of larval mortality (18.67%) and the shortest LT50 (16.20 d). Therefore, the BMkMs isolate can be developed into bio-insecticide active ingredients for controlling S. litura in tropical ecosystem.