Low temperature induced cryoprotectant synthesis by the infective juveniles of Steinernema carpocapsae: Biological significance and mechanisms involved

The infective juveniles (IJs) of Steinernema carpocapsae synthesised trehalose but not glycerol at low temperatures. Equilibrium trehalose levels were temperature dependent. When the IJs were incubated aerobically in tap water at temperatures ranging from 2 to 14°C, their trehalose levels increased from 1.9% dry weight to equilibrium levels ranging from 3.4% at 14°C to 6.0% at 5 ~ 8°C. Noticeable increases in trehalose levels in the IJs of four other species of entomopathogenic nematodes (ENs) exposed to 5°C indicated that this is likely to be a common characteristic of the IJs of ENs. Cold induced IJs had a much higher tolerance to severe osmotic dehydration. When aging IJs, which have lower energy reserves than fresh ones, were exposed in the same way to 5°C for 7 days, their trehalose levels were lower than those of fresh IJs but the survival rates of the IJs did not drop substantially. Changes in lipid, glycogen and protein levels of IJs during cold induction and subsequent recovery indicated that trehalose was not synthesised from glycogen, but from lipids and/or proteins. The processes involved in low temperature induced cryoprotectant synthesis by ENs are discussed and compared to those found in insects.