Effect of the Bacteria Bacillus Subtilis, Bacillus tequilensis strain C44 and Bacillus tequilensis strain 52 in the Control of Larval Stages of the Beetle Callosobruchus maculatus in the Laboratory

Abstract

The effect of Bacillus tequilensis strain C44 isolated from soil, Bacillus subtilis isolated from the insect, and Bacillus tequilensis strain 52 also isolated from the soil on the mortality of the second and fourth larval instars of the southern cowpea beetle (Callosobruchus maculatus (Fab.)were investigated. Twenty bacterial isolates were collected, and a number of them were selected after morphological and microscopic identification and used in treating the larval stages of the southern cowpea beetle, C. maculatus. Three isolates that gave effective control results, were then selected and identified by PCR. The PCR products separated by electrophoresis on agarose gel showed a 1250 bp band for the probiotic bacteria. Diagnosis confirmed that the bacterial species were Bacillus tequilensis strain C44, Bacillus tequilensis strain C52, and Bacillus subtilis. A biological test was conducted for these isolates at three concentrations (2.5, 5.0 and 10.0 mg/ml), in addition to the control treatment. The results obtained showed that the highest mortality rate was obtained when using Bacillus tequilensis C44 at a 10% dilution to treat the second larval stage (100.0%) and for the fourth larval stage (80%), 7 days after treatment. The lowest mortality rate was 13.3% for the second larval stage and 20.0% for the fourth larval stage when the dilution of 2.5 mg/ml was used, one day after treatment. When Bacillus subtilis bacteria was used, the highest mortality rate of the second stage larvae was achieved with a 10% dilution (100.0%), whereas the highest mortality rate of the fourth larval stage of 86.7% was achieved 7 days after treatment. The lowest mortality rate was 26.7% for the second larval stage and 20.0% for the fourth larval stage, one day after treatment with a concentration of 2.5 mg/ml. Furthgermore, when Bacillus tequilensis strain 52 was used, the results obtained showed that the mortality rate increased with the increase in the time period after treatment, and the highest mortality rate of the second larval stage reached 100% and 80% of the fourth stage larvae when 10% dilution was used, 7 days after treatment. The lowest mortality rate was 13.3% for the second larval stage at a dilution of 2.5 mg/ml and 0.00% for the fourth larval stage, one day after treatment. The study results showed that the second larval stage of the insect was more sensitive than the fourth stage, and that the mortality rate increased with increasing concentration.

Keywords:

Callosobruchus maculatus (fab). Bacillus tequilensis, Bacillus subtilis.