Management of entomopathogenic fungi in cultures of Tenebrio molitor (Coleoptera: Tenebrionidae)

Larvae of mealworms Tenebrio molitorL. (Coleoptera: Tenebrionidae) have been used as animal feed, but fungal pathogens rapidly downsize the populations, resulting in economic losses. In this work, we established an effective management strategy for fungal pathogens. An entomopathogenic fungus, Beauveria bassiana, was isolated from mealworm cadavers. The bioassay of some isolates of this species at >90% relative humidity revealed that the ERL1575 isolate had the highest virulence. At 20-30% RH, ERL1575 conidia when ingested produced 80% mortality but when sprayed topically produced only <10% mortality. Mealworms that had ingested conidia were exposed to 20, 25, 30 and 35°C and high humidity (>95%) for 5 days. This experiment produced about 90% mortality except at 35°C where mortality was <20%. When 40 fungicides were assayed against ERL1575, fluazinam (1000-fold) and mancozeb (667-fold) significantly inhibited conidial germination and/or hyphal growth. When fluazinam and mancozeb were added to the mealworm diet of conidia-inoculated wheat bran, most were alive 3 days post application. However, 100% mortality resulted 3 days post application in the conidia-inoculated wheat bran without any fungicides. In conclusion, B.bassiana isolates are pathogenic at <30°C when they are ingested by mealworms but fluazinam and mancozeb can be used for management to control the pathogen in their cultures.