Lesser mealworm Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae) larvae are differentially susceptible to Beauveria bassiana (Bals.-Criv.) Vuill. (Hypocreales: Clavicipitaceae) under moderate and extreme high temperature stress.

Lesser mealworm larvae topically treated with Beauveria bassiana, under different temperature regimens demonstrated complex interactions with the pathogen. Larvae treated with B. bassiana and incubated at 32.5 °C were less susceptible to B. bassiana than those treated in the same way but then incubated at 25 °C. Larvae incubated at 35 °C for two days after B. bassiana treatment showed limited susceptibility to disease, but those incubated at 35 °C two days prior to treatment and then incubated at 25 °C immediately after B. bassiana treatment were more susceptible than those maintained at 25 °C prior to and after treatment. All mycosed larvae incubated at 25, 32.5, or 35 °C prior to fungal treatment exhibited B. bassiana conidiogenesis. Larvae incubated at 35 °C immediately after B. bassiana treatment exhibited limited mortality after seven days, but succumbed when they were transferred to 25 °C. Larvae maintained at 35 °C for 14 days after B. bassiana treatment showed moderate susceptibility, but exhibited significantly less mortality and conidiogenesis than the larvae transferred from 35 to 25 °C. Conidia incubated at 25 °C on agar plates germinated faster than conidia incubated at 32.5 °C. Conidia incubated at 35 °C did not germinate after 7 days, but germinated within 24 h when transferred to 25 °C.