Compatibility of entomopathogenic nematodes with natural enemies for horticultural pest control

Entomopathogenic nematodes (EPNs) have been recently tested against target pests located on crop foliage with encouraging results. In these orchard environments, predator and parasitoid insects (natural enemies) are commonly released. However, the possible effect between these biological control agents has barely been approached. The aim of this study is to investigate the survival of four predator and four parasitoid species commonly used in horticulture exposed to EPNs under laboratory conditions. A first assay was done in Petri dishes with a dose of 100 IJs cm(-2) of three different EPNs treatments separately. The results showed no effect of Heterorhabditis bacteriophora treatment on insect survival for 48 h. Moreover, natural enemies registered a survival rate of over 75% with Steinernema feltiae treatment. These two EPNs were considered harmless according to the IOBC classification for side effects. In Steinernema carpocapsae treatment, parasitoids and predator nymphs had a survival rate of up to 76% while, in adult predators, survival ranged from 14% to 100%. Nematode infection and entry were also evaluated. The second assay tested the compatibility of insects with S. carpocapsae under more realistic conditions using a foliar application of 4000 IJs ml(-1) on tomato plants. No insect species presented differences in survival between nematode and control treatments. The evaluation of EPN persistence showed that only half of the nematodes applied were still alive after seven hours. The three EPNs proved to be harmless to the natural enemies tested, with the discontinuous contact that a plant pot experiment involves. These results showed good compatibility between the natural enemies and EPNs tested, which should be confirmed in field conditions.