First results on the effect of Bacillus thuringiensis kurstaki on meal moths in a mealworm farm

Abstract

Abstract The mediterranean flour moth (Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), is a common pest species in mealworm farms as they thrive in a similar environment and on similar feedstock as the mealworm. Although the larvae of the moth do not directly affect the mealworm larvae, they do compete for feed. Furthermore, the webbing may cause technical issues when harvesting or processing the mealworm larvae. Yet, most of the known ways to eradicate the moths are not usable in a mealworm farm due to the harmful effects on the mealworms. In this study, the potential of Bacillus thuringiensis var. kurstaki (Btk) was assessed as these bacteria produce toxins that are specific to the order of Lepidoptera and therefore should not harm mealworms (Order: Coleoptera). Two experiments were conducted to assess the effect of Btk on E. kuehniella, mealworm (Tenebrio molitor) and a combination of both species in conditions similar to these encountered in a mealworm farm. The use of 10 (experiment 1) or 12 (experiment 2) concentrations allowed us to assess a broad concentration range (0-250/1000 ppm) and determine the 50% lethal concentration (LC50). The results indicate that Btk, within the assessed range (up to 1000 ppm), had minimal effect on the mealworm larvae, especially the final yield per cup. Nevertheless, further research is needed to determine any impact on the smaller life stages or any sublethal effects. As expected, the meal moths were negatively affected by Btk with a LC50 between 48 ppm and 332 ppm. Based on these results, the use of Btk in mealworm farms to combat meal moth seems promising. Further research is needed to finetune the application and concentration of Btk ensuring minimal use while maintaining effectiveness.