Efficacy of indigenous isolates of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycota: Hyphomycetes) against the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae)

Background The Colorado potato beetle (CPB) Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) is one of the most damaging pests of potatoes all over the world as well as in Turkey. Both adults and larvae of this pest feed on the foliage of potatoes, and often cause complete defoliation of potato plants, with considerable yield losses of up to 60%. Chemical control of this pest has induced the selection of resistant CPB populations and negative environmental impact. The aim of the present study was to evaluate the pathogenicity of 14 Turkish isolates of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycota: Hyphomycetes) against different stages of CPB under laboratory conditions. Results All isolates were tested as conidial suspensions of (1 x 10(7) conidia/ml), using spray method. The results from pathogenicity assays showed that virulence of tested isolates was variable, and mortality increased with the time of exposure. The highest mortality was seen in larvae of CPB; however, young larvae (1st and 2nd instars) were more susceptible to fungal isolates than older ones (3rd and 4th instars). Four isolates (BbDm-1, BbDs-2, BbMg-2, and BbMp-1) were more pathogenic than others against L. decemlineata, causing mortalities between 96.7 and 100% in the 2 youngest larval instars, respectively, between 91.7 and 96.7% in the 2 oldest larval instars, respectively, and between 93.3 and 96.7% in 0-48-h-old adults, respectively, 9 days post treatment. Furthermore, these 4 isolates had the most potent egg-hatching inhibitory effects (66.7-90%). The results of molecular phylogenetic analyses based on the ITS region sequence indicated that all tested B. bassiana isolates showed a high similarity (99%) with other B. bassiana isolates in GenBank. Conclusions Results suggested that the 4 B. bassiana isolates were highly virulence and had the potential for biological control of CPB. Further tests under field conditions are recommended to validate the laboratory results.

Automated summary

The study evaluated the pathogenicity of 14 Turkish isolates of Beauveria bassiana against different stages of Colorado potato beetle, showing high virulence in causing mortality in both larvae and 0-48-h-old adults. Molecular phylogenetic analyses indicated a high similarity of these isolates with other B. bassiana isolates in GenBank. Further field tests are recommended to validate the laboratory results.