a1 Department of Biology, Imperial College of Science, Technology and Medicine, Silwood Park, Ascot, Berks SL5 7PY, UK
The behaviour and infectivity of the infective juveniles (IJs) of two species of entomopathogenic nematodes, Steinernema carpocapsae Weiser and Steinernema feltiae Filipjev (Rhabditida: Steinernematidae), were determined after exposure to two neuroactive pesticides, oxamyl and fenamiphos, widely used against plant parasitic nematodes. Oxamyl (50 μg ml−1) initially stimulated non-sinusoidal movement in S. feltiae but had no appreciable effect on IJs of S. carpocapsae, while fenamiphos (10 and 50 μg ml−1) increased and sustained non-sinusoidal movement in both species over an observation period of 48 h. The two pesticides reduced the infectivity of both nematode species against late instar larvae of the wax moth, Galleria mellonella L. in a sand-tube bioassay when compared with controls. Infective juveniles of S. feltiae showed limited body waving behaviour on the sand surface whereas S. carpocapsae showed the full range of nictation movements, including body waving, stationary straight postures and leaping. Oxamyl had no significant (P>0.05) effect on the number of IJs of S. carpocapsae which nictated except when the IJs were pre-incubated with this compound for 24 h (P<0.05). In contrast, fenamiphos completely suppressed all nictation and body waving behaviour in both species. Nictating IJs of S. carpocapsae exposed to late instar G. mellonella for 12 h in a filter-paper bioassay were found to be more infective compared with non-nictating IJs. Treating IJs of S. carpocapsae with oxamyl (50 μg ml−1) increased the infectivity of non-nictating IJs compared with controls but reduced infectivity of nictating IJs when exposed to G. mellonella for 12 h. The work is discussed in relation to proposals to use these or other pesticides to enhance the activity and infectivity of IJs of entomopathogenic nematodes.
(Accepted October 16 1995)
c1 Author for correspondence