Entomopathogenic fungi represent excellent candidates for biological insecticides. Among the many entomopathogenic fungi, Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae) is one of the most promising species. Here, we report the results of infection studies performed using four B. bassiana native isolates (Bb37, Bb38, Bb4, and Bb45) compared with the commercial product Mycotrol® (strain GHA) on adult Mexican bean beetle Epilachna varivestis Mulsant (Coleoptera: Coccinellidae), one of the most important pests of bean production in Mexico. First, single concentration (1 × 18 conidia mL−1) assays were carried out using all isolates applied using an immersion method. Examinations at 1 days after inoculation indicated that isolates Bb37, Bb38, and Bb4 significantly reduced adult survival, causing 6–75% mortality compared to the commercial strain GHA (33%) and control (29%). Second, using two selected isolates (Bb37 and Bb4), the mean lethal concentration values (LC5) were estimated for third instar larvae and adult E. varivestis. The LC5 values for Bb37 and Bb4 isolates decreased 5.26-fold and 3.19-fold, respectively, in third instars compared with adults. However, such difference for Bb4 isolate was not significant. Finally, an experiment, to compare the median survival time (MST) values between third instar and adult E. varivestis, was conducted using Bb37 and Bb4 at 1 × 19 conidia mL−1. MST values were significantly reduced against larvae (87 and 1 h) compared with adults (13 and 134 h) by Bb37 and Bb4, respectively. We conclude that native isolates of B. bassiana represent an important alternative for the control of E. varivestis. However, to demonstrate its effectiveness under field conditions, detailed studies are needed.
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