SUSCEPTIBILITY OF LESSER MEALWORM (COLEOPTERA, TENEBRIONIDAE) TO BEAUVERIA-BASSIANA (MONILIALES, MONILIACEAE) - EFFECTS OF HOST STAGE, SUBSTRATE, FORMULATION, AND HOST PASSAGE

Mature lesser mealworm (Alphitobius diaperinus (Panzer)) larvae were susceptible to infection with Beauveria bassiana (Balsamo) when larvae were shaken with conidia in an aqueous suspension or in a starch dust. Approximately 98 and 60% larval mortality rates were observed two weeks after exposure to suspensions containing 5 x 10(7) conidia per ml of aqueous suspension or 2.5 x 10(8) conidia per gram of dust, respectively. Substantially lower larval infection rates (< 30% mortality at all doses) were observed when aqueous suspensions of conidia (high rate of 5 x 10(7) conidia) were applied to almost-equal-to 250 cm3 of used poultry litter containing beetle larvae; dust-treated litter resulted in mortality similar to forced-contact assays. Mortality was higher when larvae were exposed to extruded polystyrene insulation treated at 7.3 x 10(6) conidia/cm2 than when larvae were exposed to weathered plywood treated at the same rate. The fungus used in the tests was originally isolated from and subsequently produced in adult house flies (Musca domestica L. [Diptera: Muscidae]); a single passage through mature A. diaperinus larvae resulted in a substantial increase in virulence for A. diaperinus larvae. Mortality among adult beetles was low (< 27%) in all assays.