Effect of passing Beauveria bassiana through alkane based media on the adult mortalities of Rhyzopertha dominica and Sitophilus oryzae

Abstract

Entomopathogenic fungi have been investigated for management of stored product pests as alternatives to chemical control. Beauveria bassiana is commonly considered and thus increasing its efficacy has also been studied. The purpose of this study is to evaluate the effect of passing two B. bassiana cultures (wild and singlespore cultures) through n-hexadecane and n-octocasane based media on Rhyzopertha dominica and Sitophilus oryzae adult mortalities. For each Petri plate, 2 ml of 10% alkane was spread, let to evaporate and fungus was inoculated. After sporulation, spores for pathogenicity tests were produced by solid fermentation method on rice. Pathogenicity tests were conducted by application of 500 ppm (w/w) spores in wheat on 20 adults at 25±2oC, 65±5 r.h. in darkness with five replications. The efficacy of wild culture towards R. dominica adults was enhanced in both treatments. Mortality in 7 days increased from 35% to 55 and 69% when n-hexadecane and noctocasane were used, respectively. Similarly, these treatments increased 14-day mortalities from 65% to 77 and 87%, respectively. Treatment of single-spore culture, however, either showed no change or reduced mortality. Passing both cultures through both alkane based media did not statistically affect the activity against S. oryzae. This study illustrated that increasing the virulence of B. bassiana is possible for R. dominica and increase depends both on the starting fungus culture and alkane used. Starting with a wild fungus culture with a wider genetic diversity, and using n-octocasane can produce a better enhancement.

Keywords

• microbial control
• biological control
• virulence
• entomopathogen