POTENTIAL FOR THE CONTROL OF PLUTELLA-XYLOSTELLA LARVAE WITH ENTOMOPATHOGENIC NEMATODES

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 wer e chosen for further study Use of EPNs against foliage pests is common ly perceived to be limited by their temperature range and ability to s urvive desiccation and UV radiation. The effects of these abiotic fact ors on the infective juveniles (ijs) of two isolates of Steinernema sp p. (SSL85), two isolates of Steinernema spp. (M87), Heterorhabditis n. sp., and Heterorhabditis indicus were examined. Infectivity at differe nt temperatures was found to differ both within and between species, w ith optimal infection at 20-25 degrees C. Desiccation studies revealed more marked, although not statistically significant, differences betw een the isolates. For example, at 80% relative humidity, survival of a pproximately 51% of ijs of Steinernema spp. (SSL85/25) was observed, c ompared with 13% for Steinernema spp. (M87/45). Prior exposure of ijs suspended in water droplets to simulated solar radiation resulted in r elatively constant DBM mortality in subsequent bioassays and, generall y, no marked reduction in mean infection. These laboratory-based studi es are encouraging as they suggest that entomopathogenic nematodes can tolerate, within defined limits, the major abiotic factors faced in t he foliar environment. Infection of DBM larvae was shown to have comme nced within 3 hr postexposure, resulting in significant levels of mort ality although maximal infection did not occur until at least 24 hr po stexposure. Dose-response studies showed that between 1 and 18% of the initial dose of ijs infected DBM larvae. (C) 1997 Academic Press.