BIOPHYSICAL PROPERTIES OF THE SURFACE OF DESICCATION-TOLERANT MUTANTSAND PARENTAL STRAIN OF THE ENTOMOPATHOGENIC NEMATODE HETERORHABDITIS-MEGIDIS (STRAIN UK211)

Entomopathogenic nematodes (EPN) are useful biological control agents of insect pests. However, the infective juvenile (IJ) stage which is t he only stage to occur outside the host is susceptible to environmenta l extremes such as desiccation. We have isolated desiccation-tolerant strains of the EPN Heterorhabditis megidis. In this paper we describe the surface properties of these desiccation-tolerant mutants. Heterorh abditid IJs retain the sheath of the previous larval stage. The mutant lines possess alterations in the surface properties of the sheath. Di fferences were observed in fluorescent lipid analogue insertion into t he surface of the sheath. Furthermore, cationized ferritin-binding stu dies demonstrated that the mutant lines possessed an increase in net n egative surface charge. Removal of the surface layer of the sheath res ulted in the loss of the mutant phenotype and in a reduction in the de siccation tolerance of the parental strain. Therefore, the negatively charged 'surface coat' appears to play an important role in the desicc ation tolerance of Heterorhabditis species.