Effectiveness of different species/strains of entomopathogenic nematodes for control of western flower thrips (Frankliniella occidentalis) at various concentrations, host densities, and temperatures

Entomopathogenic nematode (EPN) species/strains (Rhabditida: Steinernematidae and Heterorhabditidae) were tested at a concentration of 200 infective juveniles (IJs) per cm2 against mixed soil-dwelling life stages (i.e., second-instar larvae, prepupae, and pupae) of the western flower thrips (WFT) Frankliniella occidentalis (Thysanoptera: Thripidae), in a plant growing substrate under laboratory conditions. The different EPN species/strains resulted in WFT corrected mortality (CM) values ranging between 2.6 and 60%. In general, Heterorhabditis spp. were more virulent than Steinernema spp. Increasing concentrations of selected EPN species/strains led to an increase in thrips CM, with significant differences among species/strains. Heterorhabditis indica LN2 caused higher CM than the other strains, with 30 and 90% as highest CM at the lowest and highest concentration tested, i.e., 100 and 1000 IJs cm−2, respectively. In an experiment with different WFT densities, CM caused by Steinernema bicornutum negatively correlated with host density. However, with H. indica LN2, CM increased, though not always significantly, with increasing host densities. Generally, the effect of host density on efficacy of EPNs depended on concentrations. When tested over a range of temperatures, 25 °C was the optimal temperature for both H. indica LN2 and S. bicornutum. H. indica LN2, tropical in origin, and S. bicornutum, isolated from a more temperate environment, performed better at higher and lower temperatures, respectively.