Influence of temperature and duration of storage on the lipid reserves of entomopathogenic nematodes

Lipids represent the main source of energy in entomopathogenic nematodes. In the infective juvenile (IJ) phase, the level of such reserves can be influenced by storage, and this may affect their infectivity. The aim of this study was to evaluate the percentage of lipids and the associated infectivity in IJs of Steinernema carpocapsae, S. riobrave, Heterorhabditis sp. JPM4, Heterorhabditis sp. CCA and Heterorhabditis sp. PI that had been stored under different temperatures (8-28°C) for various times (0 to 180 days). The amounts of lipids present in IJs were evaluated histologically using a colorimetric method, while infectivity was assayed against Galleria mellonella larvae. Lipid levels diminished with increasing storage time for all nematodes, but the rates of decrease varied according to storage temperature and species. Lipid reserves were conserved for longer storage periods at 8, 16 and 20°C, while at 24 and 28°C the percentage of lipids decreased rapidly. The infectivities of IJs of Heterorhabditis spp. were less tolerant than those of Steinernema spp. to temperatures of 8, 24 and 28°C. Thus, while storage at 8°C was optimal for conserving lipid reserves, infectivity was best preserved at temperatures of 16 and 20°C gave rise to the least reduction in infectivities after 180 days of storage. In this way, lipids and infectivity are influenced by different storage temperatures for the species tested. These data are useful for greater success in using entomopathogenic nematodes as biocontrol agents.