Synergistic effect of Metarhizium flavoviride and Serratia marcescens on western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)

Background The western flower thrips (WFT), Frankliniella occidentalis Pergande ( Thysanoptera: Thripidae ) , is an important polyphagous pest in both greenhouses and fields. Due to its wide range of host plants and short life cycle, the pest causes overwhelming damage and has led to the destruction of many crops. The combined use of entomopathogenic microorganisms could be an important option to overcome the difficulties in controlling WFT. The virulence of thirty local entomopathogen isolates was tested on WFT, and possibilities of combined application for WFT control were investigated. Results All isolates were virulent for both the second larval stage and the adult stage of WFT. Serratia marcescens Se9 was the most virulent bacterial isolate with a mortality of 54 and 69.6% against the second larval and the adult stages of WFT, respectively. The LC 50 values of the Se9 isolate were determined to be 4 × 10 6 cfu/ml for the second larval stage and 6.3 × 10 6 cfu/ml for the adult stage. Among the fungal isolates, Metarhizium flavoviride As18 showed a mortality rate of 92.1 and 74.5% against the second larval and the adult stages of WFT, respectively. The LC 50 value was determined to be 1.6 × 10 4 and 7.1 × 10 4 conidia/ml for the second larval and adult stages of WFT, respectively. The combined application of S. marcescens Se9 and M. flavoviride As18 at different concentrations generally performed better than single treatments, indicating an additive or synergistic interaction. While the single treatment with S. marcescens and M. flavoviride caused a mortality of 20.4 and 49.5%, respectively, the combined application ( S. marcescens LC 25 ; M. flavoviride 100 × LC 25 ) resulted in a mortality of 95.7% of the second larval stage. Similarly, the combined application caused 96% mortality in the adult stage, while the single treatments with S. marcescens and M. flavoviride caused 11.3 and 61.3% mortality, respectively. Conclusion The study showed that the combined application of S. marcescens (LC 25 ) and M. flavoviride (LC 25 × 100) resulted in synergism against both second larval and adult stages of WFT. This is the first study to show that the combination of S. marcescens and M. flavoviride had synergistic potential to suppress the WFT population. In future studies, these microorganisms should be formulated together as biopesticides and tested under greenhouse or field conditions.