Suitability of Cordyceps bassiana and Metarhizium anisopliae for biological control of Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae) in an organic Mexican banana plantation: laboratory and field trials

The banana root borer [Cosmopolites sordidus Germar (Coleoptera: Curculionidae)] is the most harmful insect pest currently affecting organic banana plantations in Mexico. The use of entomopathogenic fungi to control C. sordidus populations is a biological control method that presents a promising alternative to conventional means. This study aimed to evaluate the virulence of native isolates of entomopathogenic fungi Cordyceps bassiana and Metarhizium anisopliae against C. sordidus adults under laboratory and field conditions. In laboratory assays, 12 isolates of C. bassiana and nine isolates of M. anisopliae were tested. In field trials, Cb174 (C. bassiana) and Ma148 (M. anisopliae) isolates and their co-application were evaluated. Cordyceps bassiana isolates Cb171 and Cb174 resulted in adult mortalities of 80.2 and 77.5% and had the lowest median lethal concentrations (LC50) of 6.4 x 10(6) and 5.4 x 10(6) conidia mL(-1), respectively. Regarding the median lethal time (TL50), the most virulent isolates of C. bassiana were Cb171 and Cb190 with 9.49 and 9.55 days, respectively. For M. anisopliae, the Ma148 isolate was the most virulent (LC50 = 8.6 x 10(6) conidia mL(-1) and LT50 = 12.61 days) and led to an adult mortality of 76.9%. In field trials, two tested isolates (C. bassiana Cb174 and M. anisopliae Ma148) were both able to reduce C. sordidus populations by 48.5% and their co-application by 38.1%. Percentage of mycosis in captured adults was over 50% for the entire evaluation period (1.6 months), which confirms the efficacy of entomopathogenic fungi. Both Cb174 and Ma148 are good candidates for developing formulated products to use in the integrated pest management of C. sordidus in Mexican organic banana plantations.