IMPACT OF ENTOMOPATHOGENIC NEMATODES ON THRIPS TABACI LINDEMAN(THYSANOPTERA: THRIPIDAE) LIFE STAGES IN THE LABORATORY AND UNDER SEMI-FIELDCONDITIONS

The biocontrol potential of entomopathogenic nematodes (EPNs) against soil -dwelling life stages of the onion thrips, Thrips tabaci Lindeman (Thysanoptera: Thripidae) was evaluated under laboratory and semi-field conditions. The pathogenicity of native isolate of Steinernema feltiae (T1) and three commercial strains, S. feltiae, S. carpocapsae (Rhabditida: Steinernematidae) and Heterorhabditis bacteriophora (Rhabditidae: Heterorhabditidae) were tested at concentrations of 400 and 1000 infective juveniles (IJs)/cm 2 against the second instar larvae (L2), prepupae and pupae of the thrips. This was followed with trials compared efficacy of S. carpocapsae on the thrips fed on dif ferent host plants, i.e. onion shoots, Allium cepa (L.), pods of green beans, Phaseolus vulgaris (L.) and cucumber fruits, Cucumis sativus (L.). In the semi-field experiments, effects of two EPNs, S. carpocapsae and H. bacteriophora, at concentrations of 10 4 or 2×10 4 IJs/ml against the thrips larval stage were tested. Our results showed that the highest onion thrips corrected mortality (CM) was recorded for prepupae (92%) and pupae (92.59%) at 1000 IJs/cm 2 by S. feltiae (T1) and S. carpocapsae, respectively and the mortality caused by the commercial strain of S. feltiae against thrips larval stage at 400 IJs/cm 2 was the lowest rate (CM= 3.7%). Among different host plants, green bean feeding induced the highest CM by S. carpocapsae at 1000 IJs/cm 2 against the onion thrips larvae. In the semi -field experiments, application of two concentrations of EPNs had no significant effect on the larval mortality, compared to the control treatment.

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