Effect of temperature and soil moisture on the efficacy of indigenous and imported strains of the entomopathogenic nematode, Heterorhabditis sp. against the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera/Noctuidae)

Background Biotic and abiotic factors influence survival, infectivity, development, reproduction, and activity of the entomopathogenic nematodes (EPNs). EPNs have been used to suppress the soil-inhabitant insects, which applied as a successful biological control agent against the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera/Noctuidae) larvae, and pupae. Results Studying the effect of different temperatures 20, 25, and 30°C ± 2, and the soil moisture content at 10, 15, and 25% on the susceptibility of two Heterorhabditis sp. strains, Egyptian strain (TAN5) and imported strain (Hb 88 ) against the A. ipsilon 4th and 6th larval instars and 3-day-old pupae was carried out under laboratory conditions. The tested concentrations of the two strains were 30, 60, 120, 240, and 480 IJs/cm 2 of soil surface. The mortality rate of 4th instar A. ipsilon larvae was high after Heterorhabditis strain TAN5 treatments at all concentrations, which ranged between (24 and 100%) and (6–100%) at 25°C and 30°C, respectively. At 20°C, Heterorhabditis strain Hb 88 recorded higher mortality percentages for A. ipsilon 4th and 6th larval instars and pupae than the indigenous strain TAN5. The soil moisture content of 25% gave the highest mortality rates for the 4th instar larvae of A. ipsilon after treatments of the two strains. The Egyptian Heterorhabditis strain TAN5 was tolerant to the increase in temperature and more tolerant to the change in the water content of the soil than the imported strain Hb 88 at all concentrations tested. In a semi-field experiment, Heterorhabditis strain TAN5 at concentrations between (1000–8000 IJs/cm 2 of soil surface) showed mortality rates (27–95%) for 4th instar A. ipsilon larvae and (19–81%) for the 3-day-old pupae, respectively. Conclusions Heterorhabditis strains TAN5 can was utilized against the black cutworm of A. ipsilon at the temperatures 25 and 30°C. Heterorhabditis strains TAN5 and Hb 88 can be utilized against the black cutworm of A. ipsilon at the soil moisture content from 15 to 25%. In the semi-field experiment, Heterorhabditis TAN5 and Hb 88 strains were effective against larvae and pupae of A. ipsilon at high concentrations of the nematodes.