Entomopathogenic nematodes against foliage feeding crucifer pests in the tropics

Use of entomopathogenic nematodes against foliage pests is commonly perceived to be limited by their tolerance to temperature, desiccation and UV radiation. The effect of these abiotic factors on the infective juveniles (ijs) of two isolates of Steinernema spp. (SSL85), two isolates of Steinernema spp. (M87), Heterorhabditis n.sp. and H. indicus recovered from selected sites within Peninsular Malaysia was examined. Infectivity at different temperatures was found to differ both within and between species, with optimal infection generally at 25 °C. Desiccation studies revealed more marked differences between the isolates. For example, at 80% relative humidity, survival of approximately 51% of ijs of Steinernema spp. (SSL85/25) was observed, compared with 13% for Steinernema spp. (M87/45). Prior exposure of ijs suspended in water droplets to simulated solar radiation resulted in a general decline in % mortality of Plutella xylostella larvae in subsequent bioassays but no marked reduction in mean infection. These preliminary studies are encouraging as they suggest that entomopathogenic nematodes can tolerate, within defined limits, the major abiotic factors faced in the foliar environment. The results are discussed in terms of application under foliar conditions.