Comparative study on the effect of two Bacillus thuringiensis strains of the same serotype on three coleopteran pests of stored wheat.

The biological control of insect populations of stored products by insect pathogens such as, Bacillus thuringiensis (Berliner) is considered as an alternative to synthetic insecticides. So far, only B. thuringiensis among microbial pesticides have been approved for application against stored product insect pests. In this study we used a laboratory culture from an indigenous isolate of B. thuringiensis subsp. morrisoni, and the commercial formulation, B. thuringiensis subsp. tenebrionis. The bioassays with adults of the three beetle species (Rhyzopertha dominica (F.), Silophilus granarius (L.), and Tribolium confusum (Jacqueline du Val) and larvae of T. confusum were done at four different concentrations 3000, 1000, 500, and 250 ppm. Mortality records were made after 7, 14, 21, 28 days of exposure. Among the strains tested, the indigenous isolate B. thuringiensis subsp. morrisoni gave the highest mortality for adults of R. dominica and T. confusum after 21 and 28 days of exposure. It was (67, 78%) and (43, 65%), respectively. Larvae of T. confusum showed that the isolate, morrisoni was the most active where it gave mortality records of 76, 60, 55 and 35% at 3000, 1000, 500 and 250 ppm after 28 days of exposure, while the other strain did not show any actual mortality. This demonstrates the possibility of using B. thuringiensis subsp. Morrisoni for the protection of stored grains from pest infestation.