Effect of Bacillus thuringiensis Berliner against Khapra beetle, Trogoderma granarium Everts (Dermestidae: Coleoptera)

The present study was conducted in the Entomology Laboratory of the Postgraduate Studies Division at the Department of Plant Protection, College of Agricultural Engineering Sciences, University of Baghdad, during the period from October 1, 2024 to May 30, 2025. The main objective of this research was to evaluate the insecticidal efficacy of Bacillus thuringiensis Berliner against the Khapra beetle (Trogoderma granarium Everts) and to investigate its potential for use in the biological control of this economically significant pest. The findings revealed that the application of B. thuringiensis spores had a notable impact on the mortality rates of both adults and various larval instars (second through fifth) of T. granarium. The bacterium was applied at three different concentrations: 1 × 10⁵, 2 × 10⁵ and 1 × 10⁶ spores/mL. The two higher concentrations, 2 × 10⁵ and 1 × 10⁶ spores/mL, produced the most pronounced effects, with the highest mortality percentages recorded at seven days post-treatment. Specifically, mortality rates in adults reached 85.40% and 90.42%, respectively. For the second instar larvae, the mortality was 89.45% and 93.82%, while in the third instar larvae, the rates were 90.62% and 96.65%, respectively. Similarly, fourth instar larvae showed mortality rates of 78.00% and 83.22%, and fifth instar larvae exhibited 74.75% and 79.52% mortality, respectively, following seven days of exposure. The study also highlighted variation in the susceptibility among larval stages. The third instar larvae were the most sensitive, with a peak mortality rate of 91.07%, whereas the fifth instar larvae were the least affected, with a mortality rate of 72.76%, both observed after seven days of treatment. Furthermore, increasing concentrations of B. thuringiensis were associated with reduced seed germination loss and lower weight loss in grains infested with T. granarium. The concentration of 1 × 10⁶ spores/mL resulted in the lowest grain weight loss (11.56%) and lowest germination loss (43.33%), in contrast to the untreated control group, which exhibited significantly higher losses: 13.48% in grain weight and 50.33% in seed germination.