Studies on the Susceptibility of Spodoptera exigua (Hubner) Larvae to Bacillus thuringiensis Under Greenhouse Conditions

In this study, susceptibility of the first three larval stages of Spodoptera exigua to Bacillus thuringiensis was investigated. To determine the LC50 values for each larval instar, 6 different logarithmic concentrations of Bacillus thuringiensis were used. A control was also included in each of the bioassays. The value of LC50 for 1st instar larvae, that had been treated one to four hours after hatching, was 311.617 ppm. For the 2nd and third instars, the larvae values of LC50 were 1356.95 and 2708.27 ppm, respectively. It was clear that larval susceptibility to Bacillus thuringiensis decreased with age. In order to enhance the Bacillus thuringiensis efficiency to control Spodoptera exigua under field conditions, Bacillus thuringiensis should be applied at egg hatch peaks.