Study on the efficiency of Beauveria bassiana after harvest of rice for decrease of overwintering population of striped stem borer

In order to evaluate the effect of Beauveria bassiana fungus on decrease of overwintering larvae populations of rice stem borer, Chilo suppressalis was studied. This study was carried out based on factorial experiment with RCBD in 4 replications in two factor A and B during 2005-2006 in Rasht. Factor A, are as follow: (a1) Concentration of 108 conidia/ml. from spores of B. bassiana,(a2) Concentration of 106 conidia/ml. from spores of B. bassiana and(a3) Control (without treatment). Factor B, are as follow: (b1) Spraying of fungus spores by sprayer with volume 1 liter, (b2) Applying mixture of fungus spores with wood waste (granule). The plots size were 3×7 m. In this study Diazinon granules 10% was applied for prevent natural infect of SSB larvae every 15 days. A week after harvest of rice, we used fungus of B. bassiana in the field. Two days after 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. The samples units were number of surviving and dead larvae of SSB. The results showed that live and dead SSB larvae were significantly difference (P5%). In a treatment where B. bassiana was applied by concentration of 108 conidia/ml. as granules, the highest mortality of larvae observed. During 2005, a major increase in mortality larvae was obtained with fungus granules (140 dead larvae), 35% mortality) when applied at a concentration of 108 conidia/ml. But the least mortality was observed in control. By the way, results of year 2005 was similar to year 2006. Based on the results of 2006, we had a major increase in mortality larvae with fungus granules(205dead larvae from total 400 larvae from each treatment, about 51/4% mortality) when applied at a concentration of 108 conidia/ml. as granule of fungus.