Effect of temperature and relative humidity on survival of eggs and infective larvae of Ostertagia circumcincta

Survival of Ostertagia circumcincta eggs in faeces kept at 4°C and of third stage larvae (L3) kept in distilled water at −50, −25, −10, 4, 16, 25 and 35°C was studied. The effect of relative humidity (RH) of 95, 75, 50 and 30% at 16, 25 and 35°C on the survival of L3 was also studied. The survival of eggs at 4°C was high during the first week, followed by a gradual decline to 10% by Day 22 of storage. The L3 survived for 7 weeks at −50°C, 9 weeks at −25°C, 13 weeks at −10°C, and 7 weeks at 35°C. By 16 weeks, at the termination of the experiments, 74% 76% and 23% of L3 were still alive at 4°C, 16°C and 25°C, respectively. At all temperatures tested, the L3 survived longer at RH of 30 and 50% than at 75 and 95%. At 35°C, L3 survived up to 6 weeks at 30%, 5 weeks at 50% and 1 week at 75 and 95% RH. At 16 and 25°C and RH of 30 and 50%, over 70% of L3 were still alive at the end of experiments at the seventh week. At 16 and 25°C, 40% of L3 were still alive at the end 5% survived for 6 weeks at 95% RH. At 16°C at the end of experiment at the seventh week, 25% of L3 were still alive at 75% RH and 56% were still alive at 95% RH. It is concluded that the L3 of O. circumcincta are very resistant to temperature and RH.