Behavioural and physiological responses of infective juveniles of the entomopathogenic nematode Heterorhabditis to desiccation

Infective juveniles (IJs) of entomopathogenic nematodes (EPNs) are suscepti ble to a wide variety of environmental factors, including desiccation, whic h limit their usefulness as biocontrol agents. Although EPNs can be subject ed to a gradual loss of water in their natural environment they are not ful l anhydrobiotes, being able to survive only moderate levels of desiccation at high relative humidities (rh). We investigated the desiccation tolerance of IJs of several Heterorhabditis species and strains when exposed to fast and slow desiccation regimes. We also investigated the behavioural and bio chemical responses of Heterorhabditis IJs when exposed to 98% rh for 4 days . IJs of H. megidis UK211 (but not IJs of H. indica) aggregate into large c lumps when desiccated at high rh, but unlike Steinernema spp., neither H. m egidis nor H. indica IJs showed any tendency to coil. Preincubation of H. m egidis UK211 IJs at high (98%) rh enhances their ability to survive for 150 min at 57% rh. We show that preincubation of H. megidis and H. indica at 9 8% rh induces the synthesis of glycerol but not of trehalose, whereas ident ical preincubation conditions do induce trehalose synthesis in Steinernema carpocapsae and Aphelenchus avenae. The biosynthesis of glycerol rather tha n trehalose by IJs of two species of Heterorhabditis in response to moderat e levels of desiccation indicates that Heterorhabditis is unlikely to have the necessary metabolic responses to desiccation required to enable it to e nter into a fully anhydrobiotic state.