Oviposition and Hatching in Two Species of Ticks in Relation to Moisture Deficit1,2

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Abstract
Studies were done with the American dog tick, Dermacentor variabilis (Say), and the lone star tick, Amblyomma americanum (L.) (Acarina: Ixodidae), to determine the fecundity of these ticks, the resistance of eggs to desiccation, and egg viability in relation to different moisture deficits of the environmental air. The mean number of eggs deposited by undisturbed D. variabilis was 5379±31.0, with peak numbers on the 3rd day of oviposition. More than 50% of the eggs were deposited by the end of the 5th day, and more than 90% by the end of the 10th day. The mean number of eggs deposited by A. americanum females subjected to daily manipulation was 6436 ±30.3, with peak production on the 4th day. Most of the eggs were deposited early in the oviposition process. Oviposition was not influenced by the relative humidity of the environmental air at constant temperature (27°C). However, water loss from eggs was dependent upon the relative humidity. D. variabilis eggs lost more water than A. americanum eggs held under the same relative humidities. Almost all eggs hatched in undisturbed egg masses of D. variabilis when the relative humidity (at 27°C) was between 95 and 65%, but few eggs hatched in masses stored at lower humidities. Hatching of 24-hour oviposits of this species was less than in unseparated masses, except those stored at 95% RH. Hatching of eggs in 24-hour oviposits of A. americanum held under the same environmental conditions was lower than for eggs of D. variabilis. Further, few A. americanum eggs hatched at 65 or 60% RH, and none hatched at 55% RH. The data on water loss and hatching in relation to the relative humidity of the environmental air were used to estimate hatching of D. variabilis and A. americanum eggs in different vegetative types of a natural area, where records of temperature and relative humidity in these types were available. The low woody deciduousforest type was found to be most satisfactory for incubation of eggs of the 3 vegetative types studied, while a grass-herb-dominated old field provided the least satisfactory habitat for incubation.

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