Effect of combinations of entomopathogenic fungi species and incubation temperatures on the mortality of Alphitobius diaperinus Panzer (Coleoptera: Tenebrionidae)

Abstract

The objective of this work was to evaluate the effect of the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae under laboratory conditions, either individually or mixed at different concentrations, and at two incubation temperatures, against larvae and adults of the lesser mealworm (A. diaperinus). The insects were immersed in conidial suspensions at different rates of both fungi (respectively to B. bassiana and M. anisopliae 100 : 0; 25 : 75 ; 50 : 50; 75 : 25; control), containing a maximum of 1 × 108conidia/mL, for 10 seconds under agitation. They were then incubated at 26 or 32°C, and a 14-hour photophase. Four replicates of 15 insects were prepared for each treatment, containing either larvae or adults, respectively. Mortality was evaluated daily. Dead insects were disinfected in 70% alcohol and maintained in a humid chamber under the same conditions described above, to confirm death by the fungi. It was verified that confirmed mortality in the mixture was caused only by B. bassiana. When mixed, the action of the fungus at 26°C did not increase significatively against larvae, and decreased against adults. At 32ºC, the mixture increased the action of B. bassiana against larvae in two of the combinations (50% of each fungus and 75% B. bassiana + 25% M. anisopliae), but decreased in all combinations against adults. There was also a negative effect of temperature on the fungi, which were more effective against larvae at 26ºC.