Impact of entomopathogenic nematodes on different soil-dwelling stages of western flower thrips, Frankliniella occidentalis (Thysanoptera : Thripidae), in the laboratory and under semi-field conditions

The impact of entomopathogenic nematodes (EPN) on mortality of soil-dwellin g stages of western flower thrips (WFT), Frankliniella occidentalis (Thysan optera: Thripidae) with different insect stage combinations was studied in the laboratory and under semi-field conditions. In laboratory experiments, the efficacy of Steinernema feltiae strain Sylt (Rhabditida : Steinernemati dae) at a concentration of 400 infective juveniles (IJs) cm(-2) was tested against different proportions of soil-dwelling stages of WFT, i.e. late sec ond instar larvae (L2), prepupae and pupae. Soil was used as the testing me dium. S. feltiae significantly affected the mortality of all soil-dwelling life stages of WFT at all tested insect stage combinations. The proportion of late L2 in the population negatively correlated to EPN-induced mortality . WFT prepupa and pupa were similarly susceptible to S. feltiae and their p roportion in the population did not affect the EPN-induced mortality under laboratory conditions. The highest mortality (80%) was recorded when the po pulation consisted only of prepupae and/or pupae. In the semi-field study, the impact of S. feltiae, S. carpocapsae strain DD136 and Heterorhabditis b acteriophora strain HK3 (Rhabditida : Heterorhabditidae) (H. bacteriophora) at concentrations of 400 and 1000 IJs cm(-2) was evaluated against WFT rea red on green beans, Phaseolus vulgaris L., as host plant in pot experiments in a controlled climate chamber. All tested EPN strains at both dose rates significantly reduced the WFT populations. Up to 70% reduction of the WFT population was obtained at the higher EPN concentration.