مشخصات پژوهش

Entomopathogenic nematodes (EPNs) from the Steinernematidae and Heterorhabditidae families are obligate insect pathogens used as biological control agents against a broad spectrum of key pests. Regarding the economic importance of beet armyworm, Spodoptera exigua, on extensive range of plants, virulence of two species of entomopathogenic nematodes including Steinernema feltiae and S. carpocapsae were tested in laboratory conditions on last instar larva. Beet armyworm is still mostly controlled using synthetic insecticides and effective alternatives to synthetic insecticides need to be developed to reduce the pressure for insecticide resistance development and to reduce negative effects of the insecticides on natural enemies of pests and other non-target organism including humans. The virulence of EPNs was evaluated in 6 cm diameter Petri dishes lined with two filter papers. IJs were applied to the filter paper surface in 3 ml distilled water before the larvae was added to the Petri dishes individually. Concentrations used were 2, 5, 10, 20 and 40 IJs/L (per larvae) for both EPNs. Untreated controls received only distilled water. Mortality was recorded daily for 6 days starting after 48 h. The experiment was conducted twice. The LCvalues were calculated using Probit analysis. Mortality data were corrected for mortality in the untreated controls and subjected to analysis of variance followed by Duncan's mean separation test. Differences among means in all experiments were considered significant at P < 0.05. LC values for both EPNs had a good fit to the probit regression model. Spodoptera exigua last instar larvae were highly susceptible to both EPNs albeit S. feltiae proved more virulent compared with S. carpocapsae. After three days of exposure to IJs, larval mortality reached to highest level regarding both EPNs. Under S. feltiae treatment, the highest mortality rate was 93.33% (LC50 = 1.84 IJs/L; fiducial limit: 0.17- 3.81) andi n the case of S. carpocapsae mortali