Entomopathogenic nematodes (EPN), Heterorhabditis and Steinernema genera, have considerable biological control potential against soil-inhabiting insect pests. One of the most important factors for sustainable and successful biological control is their heat tolerance in released areas. To determine persistence abilities and foraging behaviour characteristics of infective juveniles (IT) of H. bacteriophora strains having tolerance to heat, one tolerant H. bacteriophora strain (HIZ) was compared with a non-tolerant strain (Hb1 1). The strain having more than 80% survival capability at the temperatures of 40 degrees C was used as the tolerant strain; the other strain with less than 30% survival rate at 40 C was evaluated as the non-tolerant strain. An outdoor experiment to evaluate persistence was carried out for 4 months. Vertical PVC columns filled with soil were used to detect foraging behaviour of the strains. The results showed that there are significant differences of persisted IJ numbers (except for one sampling) and foraging behaviour between heat tolerant and non-tolerant strains. According to the results, the tolerant strain was more persistent in soil and had better foraging behaviour than the non-tolerant strain. This study also revealed that the heat toleration ability of H. bacteriophora was positively linked to its persistence and foraging behaviour characteristics.