Activity of four entomopathogenic nematode species against young adults of Sitophilus granarius (Coleoptera: Curculionidae) and Oryzaephilus surinamensis (Coleoptera: Silvanidae) under laboratory conditions

Abstract

Four entomopathogenic nematode species (Steinernema fel-tiae, Steinernema carpocapsae, Heterorhabditis bacteriophora, and Heterorhabditis megidis) were tested in a laboratory bioassay with the aim of studying their efficacy in control of the adults of two stored grain pests, Sitophilus granarius and Oryzaephilus surinamensis. Activity of the biological agents studied was determined at three different concentrations (500, 1000, and 2000 infective juveniles [IJs] per adult) and temperatures (15, 20, and 25°C). The granary weevil mortality rate was higher than the mortality rate of the saw-toothed grain beetle. Heterorhabditis megidis proved to be the least efficient in control of both pests, while no significant differences were recorded between any of the other three nematode species. The experiment demonstrated that the entomopathogenic nematodes were most efficient in the control of S. granarius at 20°C (LC50 after 7-day exposure 803–1195 IJs/adult) and 25°C (LC50 505–1175 IJs/adult). A satisfactory level in control of the pest O. surinamensis was reached at 20°C (LC50 921–1335 IJs/adult). The concentration of the suspension used in our experiment was shown to be a less important factor affecting the biological activity of nematodes against the adults of both stored grain pests. Though the use of entomopathogenic nematodes for control of the tested pests is not possible at the present time, it may be possible to combine this approach with some other (biotechnical) methods in the future.