Insecticidal potency of entomopathogenic bacterium Bacillus subtilis on cockroach (Periplaneta americana)

The effect of exposing cockroaches to entomopathogenic bacteria isolated from the diseased specie was examined based on established parameters. Cockroaches were collected from residential areas in Akure metropolis in Nigeria using a bread and beer trap, brought to the laboratory, housed in wooden cages with wire nettings, provided with starch-based food and sterile water. Collected cockroaches were observed for the onset of possible disease symptoms amongst the population for several weeks. Resulting moribund and dead cockroaches were aseptically picked, surface sterilized and homogenized inside a sterile mortal with a buffer. Bacteria were isolated from the homogenate using various general and specialized media. Isolated bacteria include; Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Serratia marcescens, Bacillus cereus, Bacillus subtilis, Citrobacter freundii, Bacillus licheniformis, Proteus mirabilis and Enterobacter aerogenes. The bacterial isolates were used to re-infect healthy cockroaches out of which only Bacillus subtilis was able to cause disease in the cockroaches. The bacteria were then inoculated into another set of healthy cockroaches at varying concentrations to obtain the minimum lethal concentrations capable of causing disease and it was discovered that the organism was able to cause disease in cockroaches at concentration of 108 cfu/ml.
Although Bacillus subtilis is yet to enjoy a global recognition as a biocontrol agent to be used in the formulation of biopesticides compared to other organisms such as Bacillus thuringiensis, its insecticidal properties have many potential applications especially in integrated pest management (IPM) programs. Incorporation of pesticidal products - formulated using Bacillus subtilis - into IPM strategies, farmers can significantly reduce the usage of chemical insecticides thus minimizing its toxic environmental impact.