The eggs and engorged post-embryonic stages of Haemaphysalis longicornis Neumann, 1901, Ixodes holocyclus Neumann, 1899, and Rhipicephalus sanguineus (Latreille, 1806) (Ixodidae) were subjected, in the laboratory, to combinations of constant temperature and saturation deficit at different levels. Some experiments involved transferring the ticks or their eggs from low to high temperatures or saturation deficits, and vice versa.
The assumption was made that the non-parasitic stages of the ticks may be more susceptible to changes in temperature and humidity than unfed ticks, because their immobility in the field would prevent them from avoiding micro-environmental changes. This disadvantage is not shared by the unfed, questing stages.
The experiments were designed to discover whether each of the three species responded differently to temperature and humidity, and to determine the limits and magnitude of this response.
It was known that each of the three species had a distinct geographical distribution, and thus they presumably favoured different environments.
Various factors, including climate, hosts and vegetation, were considered, and an attempt was made to define the preferred environment of each species in terms of these factors. Simultaneously, a relationship was sought between the results of the laboratory experiments and the extremes of climate which each species appeared able to tolerate in the field. No attempt was made to seek a mathematical relationship, but it became obvious that the responses shown by each species to temperature and humidity in the laboratory, were reflected to some extent in their choice of habitat. These relationships are discussed.
It was found that R. sanguineus, which has a predilection for warm and sometimes arid habitats, was able to survive and develop at temperatures higher than those tolerated by either H. longicornis or I. holoeyalus. These two latter species generally favour temperate, moist climates.
The degree of tolerance which each species showed to desiccatory conditions in the laboratory was related to the aridity of their respective ranges.
The rates of development and water loss of each species also differed. Rhipicephalus sanguineus is characteristed by having a rapid developmental rate in all stages and loss of water occurs at a slow rate. Conversely, all stages of I. holocyclus develop slowly and lose water rapidly. From a quantitative point of view, both processes in H. longicornis lie between these two extremes.
Evidence is presented which suggests that the nature of dermal gland secretions and changes apparent in the integument of the ticks during the premoult phase may be related to their physiological tolerances.
The exercise has been mainly one of inductive reasoning, where the distribution of the ticks and their responses to certain physical factors in the laboratory, have been related with bioclimatic zones.
Incidental observations on the seasonal incidence of other Ixodidae together with some aspects of their biology are also presented.
It is hoped that the information contained herein may serve as a basis for further work, and that some of the data may be used to advantage in tick control programmes.