Developing microsclerotia of Metarhizium brunneum for control of lesser mealmorm, Alphitobius diaperinus (Panzer) (Coleoptera: Tenebrionidae)

Metarhizium brunneum has the potential to provide biological control of the lesser mealworm, Alphitobius diaperinus (Panzer), a worldwide pest of poultry production. Liquid fermentation techniques have been developed to produce microsclerotia, a fungal structure that represents an alternative technical product for insect control in that the microsclerotia produce infective conidia after application. Microsclerotia treatments of strain F52 were assayed against medium sized larvae by applying treatments to potting soil as either fermentation broth or as clay-based granules. Microsclerotia treatments applied as clay-based granules were also assayed against mixed-sex adults. Relative conidia concentrations (conidia/cup) in the treated soil samples were determined microscopically using a hemacytometer. Larval mortality was related to conidia density with LC₅₀ values of 8.03 x 10⁶ conidia per cup and 1.53 x 10⁶ conidia per cup for applications of broth and granules, respectively. Larvae were more susceptible to F52 compared with adults, which had an LC₅₀ of 1.67 x 10⁷ conidia per cup for microsclerotia applied as granules. Broth produced an average of 1.40 x 10⁹ conidia/ml broth while granules produce 4.14 x 10⁹ conidia/g granules (larval experiment) and 1.23 x 10⁹ conidia/g granules (adult experiment). Although conidia production seems comparable between broth and granules, granules represent a 20-fold concentration of the broth (1 liter broth produced 50 g granules).