Virulence of two strains of entomopathogenic nematodes (Rhabditida: Steinernematidae) against adults of Sitophilus granarius L. (Coleoptera: Curculionidae)

Türkiye is the country of origin for the wheat plant, and a significant portion of wheat production is concentrated in the southeastern and central provinces. One of the most serious pests affecting stored wheat grains in Türkiye is Sitophilus granarius L. (Coleoptera: Curculionidae), posing a significant threat to wheat production. This study evaluated the efficacy of two locally sourced entomopathogenic nematode (EPN) species, Steinernema feltiae (Strain 8) and Steinernema carpocapsae (Strain 27), isolated from olive and plum orchards in Bilecik, Türkiye. The experiment was conducted using four different concentrations of infective juveniles (IJs) (250, 500, 1000, and 2000 IJs/ml) at four temperatures (15, 20, 25, and 30 °C). Mortality rates of S. granarius adults were assessed over an 8-day period following the application of EPNs. Results showed that on the 8th day post-application, the lowest number of surviving S. granarius adults was recorded at the 1000 IJs/ml concentration of S. carpocapsae, with 0.63±0.47 at 25 °C. This was followed by 0.83±0.69 at 30 °C and 0.83±1.06 at 20 °C for the same nematode species. In contrast, S. feltiae exhibited higher survival rates, with 1.63±0.94 living adults at 20 °C and 2.00±0.70 at 2000 IJs/ml on the 8th day post-application. Overall, the S. carpocapsae (Strain 27) isolate demonstrated greater efficacy in infecting S. granarius adults compared to the S. feltiae (Strain 8) isolate. Both isolates exhibit significant potential for use in the biological control of S. granarius adults.