Control success with heterorhabditid nematodes varies with nematode species, isolate, production and storage conditions, and environmental conditions after application. These factors affect nematode behaviour. A model was developed that simulates movement of a nematode population in space and time from the moment of application on a sand column until penetration into a host. It was used to identify, (1) which nematode traits can best be used for improvement, and (2) what is the most promising strategy of improvement. The sensitivity of simulated control success of Heterorhabditis spp. against larvae of the black vine weevil, Otiorhynchus sulcatus, at low temperatures, to changes in nematode behavioural parameters was quantified and related to genetic or environmental variation found in the nematodes. Parameters characterizing nematode movement had little influence on simulated control success. Parameters characterizing aggregation and arrestment had a large effect on control, but there is no variation in Heterorhabditis for these traits. Parameters characterizing penetration had a moderate effect on control. The most promising option to enhance control by Heterorhabditis in this system would be to raise the proportion infectious nematodes of an isolate up to its genetic maximum, by improving production and storage conditions. Variation in biocontrol would be reduced, resulting in a more reliable product.