Pathogenicity of Beauveria bassiana (Bals.-Criv.) Vuill. and Metarhizium anisopliae (Metschn.) Sorokin against Galleria mellonella L. and Tenebrio molitor L. in laboratory assays

The pathogenicity of 23 isolates of Beauveria bassiana (Ascomycota, Hypocreales: Cordycipitaceae) and four of Metarhizium anisopliae (Ascomycota, Hypocreales: Clavicipitaceae) was tested against Galleria mellonella (Lepidoptera: Galleriidae) and Tenebrio molitor (Coleoptera: Tenebrionidae) larvae in laboratory assays, using 2•106 conidia mL-1 fungal suspensions. The commercial myco-insecticide Naturalis (Intrachem Bio Italia, Italy), containing the ATCC 74040 B. bassiana strain, was included in the assays for comparison. Mycosed larvae were counted 1, 2, 3, 7, 10, 14 and 17 days after inoculation and the cumulative mortality data were used to calculate mean survival time (MST) and lethal times (LT50 and LT95). No difference between B. bassiana and M. anisopliae were detected in the pathogenicity against the two insect species. However, a wide variability occurred among fungal isolates within species. The two B. bassiana isolates AL1 and ALB55 killed G. mellonella larvae within the shortest time (MST of 2.2 and 2.3 days, respectively), as well as the ALB55 did against T. molitor larvae (MST of 2.8 days). Naturalis was superior to these two B. bassiana isolates, causing a MST of 1.1 day or shorter on the insect larvae. Overall, G. mellonella resulted more sensitive than T. molitor, as showed also by the non-inoculated controls, for which MSTs were 7.7 and 8.4 days, respectively. Due to the rapid and effective insecticide action, the ALB55 B. bassiana isolate can be considered as a new promising candidate for the microbial pest control