Entomopathogenic nematodes (EPNs) of the genera Heterorhabditis and Steinernema are obligate and lethal insect parasites. Species and isolates of these genera exhibit differences in host range, infectivity, environmental tolerances etc. Two species of EPNs isolated from Czech Republic were used for the experiments: Steinernema feltiae (Prosenice) or Heterorhabditis bacteriophora H 221 (Pouzdřany). As insect hosts were used silkworm (Bombyx mori) and wax moth larvae (Galleria mellonella). The invasion occurred in Petri dish for different time period (0.5, 1, 1.5, 2, 2.5, 3 hours, in G. mellonella after 4, 5 and 6 hours, too). EPNs (approx. 1000 infective juveniles) were in the contact with 10 larvae of silkworm or 20 larvae of wax moth. Dead larvae were counted after 72 hours. Starving larvae were without feeding for 24 hours before the beginning of the experiment. One set of invasion with G. mellonella proceeded inside small glass tubes, where the larvae were still in a tight contact with EPNs, without the possibility of escape. In the case of the silkworm larvae, the time for 50 % mortality (LT50) is between 1 and 1.5 hour of invasion. After 2 hours of invasion, usually 90 % of larvae were efficiently invaded. After starvation, the mortality decreased. The LT50 of wax moth larvae is approx. 4 hours. This time compressed rapidly to half (2 hours) after starvation. After 4 5 hours, more than 90 % of starving larvae were efficiently invaded. Furthermore, rapidly increased mortality was observed in larvae infected by EPNs in the small glass tubes, with the LT50 < 0.5 hour by S. feltiae. To summarize, the time-dependent invasion of two insect species (B. mori and G. mellonella) by S. feltiae and H. bacteriophora was examined. The results concerning G. mellonella are in agreement with previously published, but this study presents for the first time new information about the pathogenicity of EPNs to B. mori, as these results were not yet published.