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 2×109 conidia g-1) was evaluated against adults of Tribolium castaneum, Sitophilus granarius and Oryzaephilus surinamensis. The experiments were carried out at the rates of 0, 250, 500, 750 and 1,000 mg kg-1 and exposure intervals of 5, 10 and 15 days, in 24±2°C and 50±5% r.h. Fifteen 1 kg lots of grain (one lot for each exposure time-rate) were prepared and treated with the appropriate predetermined doses. Four 50 g samples of each were taken as replications and placed in glass vials. Thirty 1-7 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 45 days to have the progeny production assessed. Means were separated by employing Tukey´s Test (P= 0.05). All main effects (dose, exposure time and insect species) as well as associated interactions were significant (P< 0.01), 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 15 days of exposure to 1,000 mg kg-1 concentration. These amounts were recorded 88.33±3.96, 78.31±2.15 and 64.99±4.4% 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 LC50 value within the exposure times was determined 452.855 mg kg-1 after 15 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 0 mg kg-1. 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.