The effect of soil characteristics on infectivity of Heterorhabditis sp., strain PRF-21 isolated from Puerto Rico was evaluated in a laboratory experiment. Four soil types collected in Puerto Rico were used: sandy from Joyuda (Mayagüez), sandy loam from Jobos (Isabela), clay from Isabela and clay loam from Juana Diaz (Fortuna). Last instar Galleria mellonelia larvae were used as indicators of pathogenicity of the nematode isolate. Data were taken at 5 intervals or STP (sampled time period): 3 days, 1, 2, 4 and 8 weeks. No significant differences were obtained attributable to soil type (factor A) nor to STP (factor B) or to the interaction of both in the number of dead Galleria larvae. Only the results from 3 STP were analyzed (3,7 and 14 days) since no dead larvae due to nematode were recovered from the other STP. On the other hand, the number of nematodes extracted from dead larvae in White traps showed significant or highly significant differences between soil type, time of exposure(STP), and in the interaction of these in the number of nematodes recovered from dead Galleria . The highest nematode reproduction was found in the sandy soil (Joyuda) and the lowest in the clay soil (Isabela). The nematode reached its highest reproduction at 7 days of exposure; before (3 days), or after (14 days), reproduction was lower. The result was the same when we consider the interaction of both factors (soil type and STP).