Selection of native isolates of Beauveria bassiana Bals. and Metarhizium anisopliae Metch. (Hypocreales: Clavicipitaceae) for control of white grub, Phyllophaga polyphylla (Coleoptera: Scarabaeidae)

This work was realized to select native isolates of entomopathogenic fungi for control of Phyllophaga polyphylla Bates. Larvae and adults infected with entomopathogenic fungi were collected from maize fields in Guanajuato, Mexico. Monosporic cultures were obtained from infected insects. In order to evaluate the virulence of this isolates, third-instar larvae of Phyllophaga spp. were collected in field and individually placed in containers during 40 days to discard those diseased. Idenfication was based on adults male genitalia. Groups of 8 larvae were randomly selected and dipped in a spore solution containing 1 x 10 ⁸ conidia/ml and Inex-A ®. Each treatment (=isolate) was replicated four times. Control specimens were treated with sterile water and surfactant. After treatment, each larva was placed in container with sterile soil and germinated corn seeds. The bioassay was conducted at 25°C and 70% RH. A total of 17 isolates of entomopathogenic fungi were obtained, 8 of which corresponded to B. bassiana and nine to M. anisopliae. The predominant host specie was P. pollyphylla. Four of these isolates (BB26, MA14, MA15, and MA19) were used for virulence bioassays due to presented the best mycelial growth and spores production. An additional isolate (BB42) was added to the assay because in previous test it showed high virulence to different insects. The most active isolate was MA24, causing 23.8% of larval mortality 28 days after inoculation. The BB38 and MA25 isolates caused 7.11 and 12.41% of mortality, respectively. Both BB42 and MA20 isolates caused <1% of larval mortality.