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-degrees-C and of third stage larvae (L3) kept in distilled water at -50, -25, - 10, 4, 16, 25 and 35-degrees-C was studied. The effect of relative hum idity (RH) of 95, 75, 50 and 30% at 16, 25 and 35-degrees-C on the sur vival of L3 was also studied. The survival of eggs at 4-degrees-C was high during the first week, followed by a gradual decline to 10% by Da y 22 of storage. The L3 Survived for 7 weeks at -50-degrees-C, 9 weeks at -25-degrees-C, 13 weeks at -10-degrees-C, and 7 weeks at 35-degree s-C. By 16 weeks, at the termination of the experiments, 74%, 76% and 23% of L3 were still alive at 4-degrees-C, 16-degrees-C and 25-degrees -C, respectively. At all temperatures tested, the L3 survived longer a t RH of 30 and 50% than at 75 and 95%. At 35-degrees-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-degrees-C and RH of 30 and 50%, over 70% of L3 were still alive at the end of experiments at the seventh week. At 25-degrees-C, 40% o f L3 survived for up to 5 weeks at 75% RH and 5% survived for 6 weeks at 95% RH. At 16-degrees-C at the end of experiment at the seventh wee k, 25% of L, were still alive at 75% RH and 56% were still alive at 95 % RH. It is concluded that the L3 Of 0. circumcincta are very resistan t to temperature and RH.