Biological Control of Overwintering Population of Striped Stem Borer, Chilo suppressalis after Harvest of Rice by Beauveria bassiana in Rice Field

In order to evaluate the effect of Beauveria bassiana fungus on overwintering larvae populations of rice stem borer(Chilo suppressalis) was studied during 2007-2008 in Rice Reaserch Institute, Rasht. This study was carried out based on factorial experiment with RCBD in 4 replications with three factors as follow: (a1) Concentration of 1× 108 conidia/ml., concentration of 1× 106 conidia/ml. from spores of B. bassiana and check(only distilled watter), (b) use of spores granular formulation, use of spores liquid formulation and(c) Time of sampling(first, second third steps).The plots size were 3×7 m., Fungus of B. bassiana used after harvest of rice in the field. After two days spraying with fungus, number of 100 larvae were released inside each plot. Sampling was carried out in three times, as follow: 45 and 90 day after releasing of larvae and before wintering plow.Two year analyze showed that the most suitable of concentration, formulation and sampling time were 1× 108 conidia/ml., granular and third step, respectively. The results showed that the highest mortality percentage average of larvae observed 1× 108 conidia/ml. (57.66) in third sampling. The least mortality was observed in check.