Abstract Entomopathogenic nematodes (EPNs), isolated in Malaysia, were screened against larvae of the diamondback moth (DBM), Plutella xylostella,to assess their potential as biocontrol agents. A number of isolates were chosen for further study. Use of EPNs against foliage pests is commonly perceived to be limited by their temperature range and ability to survive desiccation and UV radiation. The effects of these abiotic factors on the infective juveniles (ijs) of two isolates of Steinernemaspp. (SSL85), two isolates of Steinernemaspp. (M87), Heterorhabditisn.sp., and Heterorhabditis indicuswere examined. Infectivity at different temperatures was found to differ both within and between species, with optimal infection at 20–25°C. Desiccation studies revealed more marked, although not statistically significant, differences between the isolates. For example, at 80% relative humidity, survival of approximately 51% of ijs of Steinernemaspp. (SSL85/25) was observed, compared with 13% for Steinernemaspp. (M87/45). Prior exposure of ijs suspended in water droplets to simulated solar radiation resulted in relatively constant DBM mortality in subsequent bioassays and, generally, no marked reduction in mean infection. These laboratory-based studies are encouraging as they suggest that entomopathogenic nematodes can tolerate, within defined limits, the major abiotic factors faced in the foliar environment. Infection of DBM larvae was shown to have commenced within 3 hr postexposure, resulting in significant levels of mortality although maximal infection did not occur until at least 24 hr postexposure. Dose–response studies showed that between 1 and 18% of the initial dose of ijs infected DBM larvae.