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

Abstract

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 × 107 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.

Virulence of Beauveria bassiana Strains Isolated from Cadavers of Colorado Potato Beetle, Leptinotarsa decemlineata

“…This could indicate that the strains are genetically similar and that the sampling site has a relatively low effect when strains are selected naturally via the same host species. Results of a recent study [38] demonstrated significant differences in virulence among B. bassiana isolates obtained from the soil by bait method; nevertheless, genetical analysis revealed that all tested isolates had 99% evolutionary homology with other B. bassiana isolates from the NCBI database.…”

“…While in the youngest larval instars the LC 50 values for the NDBJJ-BFG strain of B. bassiana were 10 5 -10 6 , in adults the LC 50 values ranged between 10 7 and 10 8 spores/mL [37]. The highest sensitivity of the 1st and 2nd instar CPB larvae was confirmed by a recent study when some of 14 Turkish B. bassiana isolates applied at a concentration of 1 × 10 7 conidia per mL caused mortality between 96.7 and 100% while they caused lower mortality in eggs and adults [38]. Higher vulnerability of early instars towards B. bassiana is not unique for CPB as it has also been reported for some other insect pests [54,55].…”

“…A recent laboratory study of 14 Turkish isolates of B. bassiana showed high variability in mortality among the strains and developmental stages of CPB. Some isolates caused the highest mortality between 96.7 and 100% in the 1st and 2nd instar larvae [38] when they were sprayed with a suspension of 1 × 10 7 conidia per mL.…”

Tokat İli (Türkiye) orman alanlarından izole edilen yerel entomopatojen fungusların patates böceği Leptinotarsa decemlineata (Say, 1824) (Coleoptera: Chrysomelidae)’ya etkisi

“…Similarly, in another study four B. bassiana isolates (BbDm-1, BbDs-2, BbMg-2 and BbMp-1) at 1×10 7 conidia/ml were more pathogenic than the others against L. decemlineata, causing mortality between 97% and 100% on first and second instars, respectively, between 92 and 97% on the third and fourth instars, respectively, and between 93 and 97% on 0-48h adults, respectively, 9 days post treatment. The highest mortality was seen in larvae; but first and second instars were more susceptible to fungal isolates than third and fourth instars (Baki et al, 2021).…”