MECHANISMS FOR EXSHEATHMENT OF ENTOMOPATHOGENIC NEMATODES

Infective juveniles of the entomopathogenic nematodes Steinernema carpocapsae (All and Mexican strains) and Heterorhabditis bacteriophora (HB1 and NC1 strains) are ensheathed in a cuticle retained from the previous molt. Exsheathment marks the transition from the free-living to the parasitic life cycle. Chemical and non-chemical exsheathment methods were examined. S. carpocapsae exsheaths more readily than H. bacteriophora. Movement on a substrate increased exsheathment in S. carpocapsae but had no effect on H. bacteriophora. Exposure to 1% sodium hypochlorite for 5 min resulted in nearly 100% sheath removal in both species. Storage increased exsheathment, with greater than 70% exsheathed in both species after 64 days at 7-degrees-C. Agitation and carbon dioxide did not stimulate exsheathment. Temperature alone did not stimulate exsheathment, however, increased temperatures accelerated exsheathment during storage. The availability of reliable exsheathment methods will enable analysis of exsheathment behavior and clarification of the role of the sheath in entomopathogenic nematodes.