Temperature and Humidity Influence Emergence and Survival of Entomopathogenic Nematodes

Entomopathogenic nematode (Rhabditia: Steinernematidae and Heterorhabditidae) infective juveniles can survive adverse environmental conditions by remaining in the host cadaver for up to 50 days. Survival varies among the species and is dependent upon the environmental conditions to which the cadaver is exposed. Galleria mellonella larvae were infected at 25°C with one of four nematode species and then exposed to relative humidities (r.h.) of 75, 85, 96 or 100%. Significantly fewer Heterorhabditis bacteriophora and Steinernema feltiae emerged at low relative humidities, but relative humidity did not affect emergence of S. glaseri or S. carpocapsae. In a second experiment, G. mellonella were infected with nematodes at 25°C and either kept at 25°C or transferred to 5, 10 or 15°C, all at 100% relative humidity. Low temperatures significantly reduced emergence of H. bacteriophora and significantly delayed emergence of S. carpocapsae and S. glaseri but had no effect on rate of emergence of S. feltiae. A third experiment investigated survival of S. carpocapsae within the insect cadaver at 25 and 15°C and 75% r.h. At 25°C, all infective juveniles had died by day 28. At 15°C, 28% of infective juveniles survived in the cadaver after 40 days but could only emerge after the cadavers were immersed in water for 24 h. We conclude that infective juveniles of entomopathogenic nematodes can survive adverse environmental conditions for limited periods in the host cadaver, but low temperatures and relative humidities prevent emergence and the infective juveniles eventually die.