Pathogenecity of four isolates of Beauveria bassiana (Balsamo) Vuillemin on larvae of lesser mulberry pyralid Glyphodes pyloalis Walker (Lep.; Pyralidae) in laboratory conditions

Lesser mulberry pyralid, Glyphodes pyloalis Walker (Lep.; Pyralidae) is one of the most important pests of mulberry trees which is widely distributed in Guilan province. This pest is monophagous and has caused severe damages on mulberry trees in north of Iran. In order to evaluate the effect of Beauveria bassiana isolates on this insect pest this study was undertaken. The bioassays were performed by immersion method with concentrations ranging from 104, 105, 106, 107 and 108 conidia ml-1 in distilled water containing 0.03% Tween-80. For each concentration, forty 5th instar larvae were immersed into the conidial suspension for 10 seconds. Each experiment was replicated four times of 10 insects in each replicate. Control larvae were treated with distilled water containing 0.03 percent Tween-80 alone in the same way. The results showed that all fungal isolates were able to infect G. pyloalis larvae and larval mortality increased with increasing concentrations. The LC50 value was estimated 1.6 ×105, 4.8×105, 8.1×105, and 1.1×106 conidia ml-1 for IRAN 403 C, SPT 22, SP 566, and IR-K-40 isolates, respectively. Results showed that IRAN 403C isolate caused the highest mortality compared to other isolates with a mean of 95 percent mortality using 108 conidia ml-1. Also, different concentrations of these isolates reduced adult emergence significantly. The lowest adult emergence (25%±0.34) was observed in case of IRAN 403C isolate at 107 conidia ml-1 concentration and no adult emergence was observed at108 conidia ml-1 concentration. All used isolates caused mortality in larvae of lesser mulberry pyralid and IRAN 403C was the most efficient isolate among investigated isolates.