Potential of Photorhabdus temperata K122 bioinsecticide in protecting wheat flour against Ephestia kuehniella

Abstract

The present study reports investigations on the insecticidal activity of the entomopathogenic bacterium Photorhabdus temperata K122 against the Mediterranean flour moth Ephestia kuehniella. Cultured in the optimized medium, P. temperata K122 cells aged 32 h exhibited 51% growth inhibition at a concentration of 9 × 108 cells/ml. However, culture must be prolonged up to 48 h incubation in the proteose peptone medium to reach only 28.6% inhibition. At the same concentration, no adult emergence was observed in the case of larvae feeding on wheat flour treated with the whole culture of P. temperata K122 after physical lysis. Interestingly, P. temperata K122 cells in the viable but non culturable (VBNC) state retained the same toxicity level as the culturable cells. At a high concentration of 12 × 108 cells/ml, 100% mortality of E. kuehniella larvae could be reached. Insect mortality is due to toxaemia as confirmed by the absence of Variants small colony (Vsm) or P. temperata colonies in E. kuehniella tissue. The investigation of the histopathological effect of P. temperata toxins on the gut of infected E. kuehniella larvae showed destruction of the gut epithelium, appearance of large cavities and cellular disintegration.