Determination of the physiological age of Rhipicephalus appendiculatus (Acari: Ixodidae)

Abstract

A non-destructive method to determine the physiological age of Rhipicephalus appendiculatus is described. The ratio of two readily available parameters of the tick was used: body weight over scutal length. Because the latter is constant throughout life and because of the high correlation between body weight and the nutritional status of starving ticks, the ratio between the two provides a biomarker for the physiological condition of the tick in relation to the environmental factors. Two hundred laboratory ticks were followed over a period of one year at two different levels of relative humidity. Three distinct phases of physiological age indices were observed, both in male and female ticks: a steep decline immediately after moulting independent of humidity, a period of constant ratios found only when the ticks were kept at the higher humidity, and a period of gradual decline depending on the humidity. It was shown that the proposed method provides an easy and quick method to evaluate the physiological age of laboratory tick stocks. Preliminary results of the application of this method in the study of the age structure of field populations are discussed.