The temperature and humidity preferences of Haemaphysalis longicornis,ixodes holocyclus and Rhipicephalus sanguineus (ixodidae): Studies on engorged larvae

The engorged larvae of Haemaphysalis longicornis, Ixodes holocyclus and Rhipicephalus sanguineus were exposed to a range of temperatures and humidities to see whether the nature of their requirements in the laboratory were similar to the climate within the geographic range of each species. The response of H. longicornis and I. holocyclus to changes in humidity was also studied. Moulting of I. holocyclus larvae occurred from 18 to 28°C and at a saturation deficit of 4 mm Hg or less. The larvae of R. sanguineus moulted between 18 and 38°C and tolerated saturation deficits up to 35 mm Hg. The larvae of H. longicornis moulted between 15 and 38°C at saturation deficits up to 8 mm Hg. When engorged larvae of H. longicornis and I. holocyclus were exposed to very dry conditions for different periods of time and then transferred to moist conditions, the minimum pre-moult period and mortality was increased in comparison with larvae kept continuously under moist conditions. On the other hand, mortality of H. longicornis larvae was reduced in very dry conditions provided that they had been exposed to a moist environment for about 5 days previously. The larvae of I. holocyclus required at least 12 days exposure to a moist environment before any survived to moult in moderately dry conditions. The engorged larvae of both H. longicornis and I. holocyclus lost weight rapidly in dry air, whereas weight loss from R. sanguineus larvae was much slower. The rate of development was fastest in R. sanguineus and slowest in I. holocyclus.