The Use of Entomopathogenic Fungus, Beauveria bassiana (Bals.) Vuill. in Assays with Storage Grain Beetles

Chemical insecticides have been widely employed for the control of storage grain pests. This has caused such problems as insecticide resistance along with contamination of foodstuffs with chemical residues. Thus, there is a growing interest in using pathogenic control agents as alternative. In this study, the potential of Beauveria bassiana (BbWeevil™, a commercial product containing ۲×۱۰۹ conidia g-۱) was evaluated against adults of Tribolium castaneum, Sitophilus granarius and Oryzaephilus surinamensis. The experiments were carried out at the rates of ۰, ۲۵۰, ۵۰۰, ۷۵۰ and ۱,۰۰۰ mg kg-۱ and exposure intervals of ۵, ۱۰ and ۱۵ days, in ۲۴±۲°C and ۵۰±۵% r.h. Fifteen ۱ kg lots of grain (one lot for each exposure time-rate) were prepared and treated with the appropriate predetermined doses. Four ۵۰ g samples of each were taken as replications and placed in glass vials. Thirty ۱-۷ day old adults were introduced into each glass vial. Following mortality count in each exposure time, the adults (dead and alive) were removed and the vials left in the same conditions for a further ۴۵ days to have the progeny production assessed. Means were separated by employing Tukey´s Test (P= ۰.۰۵). All main effects (dose, exposure time and insect species) as well as associated interactions were significant (P< ۰.۰۱), with the exception of exposure time×insect, which was not significant. In all the experiments, mortality increased with increase in dose rates and exposure time with the highest mortality being observed after ۱۵ days of exposure to ۱,۰۰۰ mg kg-۱ concentration. These amounts were recorded ۸۸.۳۳±۳.۹۶, ۷۸.۳۱±۲.۱۵ and ۶۴.۹۹±۴.۴% for S. granarius, O. surinamensis and T. castaneum, respectively. S. granarius was more susceptible than the others, because the highest mortalities in each of the three exposure times and for all dose rates were observed in this species. The lowest LC۵۰ value within the exposure times was determined ۴۵۲.۸۵۵ mg kg-۱ after ۱۵ days for S. granarius. Results achieved from progeny indicate significant differences only between rates and insect species. For all species, the highest progeny production was observed in rate ۰ mg kg-۱. The results obtained in this research recommend that BbWeevil™ could be used to control different grain storage pests but to find longer exposure intervals and higher rates are subject to further future research.

کلیدواژه ها:

Beauveria bassiana ، Oryzaephilus surinamensis ، Sitophilus granarius ، Tribolium castaneum