Detection of Thermal Preference Range of two Endemic Isolates of Entomopathogenic Nematodes, Steinernema feltiae (Steinernematidae, Tylenchina) and Heterorhabditis bacteriophora (Heterorhabditidae, Rhabditina) for Application in Biological Control of Insect Pests

To determination of thermal preferance range, the life cycle of an endemic isolate of each common entomopathogenic nematode species in Iran, Steinernema feltiae Filipjev and Heterorhabditis bacteriophora Poinar was studied, separately. One isolate of each species collected from Tabriz and its suburb soils, were evaluated under four temprature levels viz 4±1, 15±1, 24±2 and 30±1°C on Galleria mellonella L. last instar larvae for 13 days. The experiment was carried out twice, for each isolate. The life cycle of H. bacteriophora was completed at 30±1 and 24±2 °C and IJs were appeared in 10th and 12th days post infection, respectively. At 15±1°C up to end of the experiment, only first generation (hermaphrodite females) of the species was appeared and after 312 hours, its life cycle was not completed. At 4±1°C, after 13 days (312 hours post infection) larval mortality due to nematode infectivity was not observed. For S. feltiae at 30±1°C despite insect infectivity, just first generation offsprings were emerged and second generation was not appeared. At 24±2°C the life cycle was completed and IJs observed in 8th day. At 15 ±1°C, mortality of G. mellonella larvae was occurred with one day delay compared to 24 ±2°C. The life cycle was completed and IJs appeared in 12th day. At 4±1°C, insect's mortality due to nematode infection was not observed. Results of this study showed that the preference temperature for S. feltiae activity is lower than H. bacteriophora and the thermal preference ranges should be considered as they are used for biological control of insect pests.