Influence of temperature on the reproduction of Damalinia equi (Denny)

Abstract

No development of the egg within the female Damalinia equi (Denny) occurred at 16°C. Most eggs were laid at 36°C at R.H.'s of 75% or less, but after an exposure to 44.5°C for only 1 hr females did not lay eggs. Morphogenesis proceeded to an advanced state from 27-39°C, but its completion and the subsequent hatching of the embryo only took place from 31-39°C provided the R.H. was less than 90%. A R.H. of 90% prevented hatching of the eggs. Exposure of eggs to 49°C for 2 hr was lethal. The skin temperature of the horse is influenced considerably by atmospheric temperature. The abundance of D. equi on the bodies of horses in early spring is probably due to the temperatures near the skin of the body being continuously favourable for reproduction of D. equi during the winter. Exposure to the sun can cause the temperatures within the hair coat on the upper aspects of the body to become higher than 44.5°C for more than an hour and thus can retard reproduction. The accumulative effect of repeated high temperatures could prevent an increase in the numbers of D. equi during the summer.