Effects of various stress factors on heat tolerance by Heterorhabditis bacteriophora and Steinernema carpocapsae

Centrifugation, desiccation, agitation, and handling of entomopathogenic nematodes in the laboratory during isolation, culture, storage, formulation and experimentation, influences nematode ability to tolerate adverse environmental conditions. Stress imposed by centrifugation (5-60 min), desiccation (3-9 days), agitation (3-24 h), and handling (2-10 times) reduced stress and heat tolerance in Heterorhabditis bacteriophora and Steinernema carpocapsae. Short durations of stresses (e.g., 5 min of centrifugation, 3-5 days of desiccation, 3 h of agitation and 2-4 times of handling) did not affect nematodes, whereas prolonged durations (e.g., 10-60 min of centrifugation, 7-9 days of desiccation, 6-24 h of agitation and 6-10 times of handling) significantly decreased heat tolerance. Steinernema carpocapsae tolerated stress comparatively better than H. bacteriophora by showing a significantly greater degree of heat tolerance. This study provides a basis to investigate further the effects of physical and chemical stresses in order to minimise handling of laboratory nematodes and reduce disruptions of their normal function and behaviour.