Physiological Age of Ixodid Ticks: Aspects of Its Determination and Application

Abstract

This review analyzes 30 yr of data concerning physiological age of ixodid ticks. The level and state of nutritional reserves in unfed ticks has been proposed as an index of tick physiological age. The dynamics of the use of these substances reflect tick aging. Thus, physiological age of ixodid ticks is determined by estimating the irreversible changes caused by natural vital activity in the body of unfed ticks, which inevitably raises the probability of tick death. The 4 age groups used in most studies correspond to different periods in the life of unfed ticks: the postmolting development, the commencement of active life (= questing activity), the midperiod of active life, and the final period of active life. The aging of adult ixodid ticks has been studied in natural populations and laboratory colonies of different species belonging to several genera. The dynamics of age composition through the activity season observed in adult Ixodes persulcatus, I. ricinus, and Dermacentor reticulatus from field populations correlated well with the known data on the life history of these species. Physiological age was successfully used as an indicator of the patterns of tick activization (= beginning of questing activity). Tick susceptibility to acaricides was shown to increase with tick aging. The success of maintenance, reproduction, and transmission of pathogens was found to be strongly influenced by tick physiological age. The physiological age can provide information about the present physiological status of an individual tick or a group of ticks and, on this basis, predictions can be made (for example, life expectancy, degree of response to certain factors). The physiological age does not give reliable information about the past life of ticks, in particular their calendar age. In this respect, the meaning of the physiological age of ixodid ticks corresponds to the biological (physiological, functional) age of animals, as used in gerontology, and differs from the physiological age of mosquitoes and other bloodsucking dipterans. Balashov's histological method of tick age determination successfully used by many authors, remains the most appropriate, until now. However, there is ample room for further advancement of methodologies of tick age assessment. The future methods should be based on the quantitative estimation of a number of characters (test-battery) related to different organs or systems.

Survival of Ixodes ricinus (Acari: Ixodidae) Under Challenging Conditions of Temperature and Humidity Is Influenced by Borrelia burgdorferi sensu lato Infection

“…It was observed that fat content in Þeld-collected females was slightly higher than that in Þeld-collected males and considerably higher than that in Þeld-collected nymphs. These results are in line with what is expected because fat content is a source of energy derived from each bloodmeal (Uspensky 1995). Larvae, which ingest less blood than further developmental stages (Ogden et al 1998), contain less fat than adults as they molt into nymphs.…”

Increased expression of ATG genes during nonfeeding periods in the tickHaemaphysalis longicornis

“…Reduction in hemoglobin levels seems to reflect a steady aging of ticks and can serve as a good indicator of their physiological age. 31 The level and state of nutritional reserves in unfed ticks have been proposed as an index of tick physiological age. Physiological age, which is an independent parameter in each of the active developmental stages in arthropods, has been well studied in medical entomology.…”

“…Hence, some materials that can inhibit starvation-induced autophagy might be effective as antitick or transmission-blocking drugs because tick susceptibility to acaricides seems to be shown to increase with tick age. 31 Further research into the molecular mechanism and the physiological significance of autophagy may contribute to the development of new methods for controlling ticks and tick-borne protozoa including Babesia and Theilelia parasites.…”

Diurnal Activity of Ixodes Ricinus in Denmark: Aspects of Physiological Age and Genotypic Variation

“…This goes for the physiological age based on histological observations ( BAL-ASHOV 1961 as cited by USPENSKY 1995), which currently is recognized to be the most appropriate method for determination of physiological age and for the method based on anatomical features. The anatomical and other methods have however been found to be comparable to the histological method for several tick species including I. ricinus (USPENSKY 1995). For the individual tick, the observed age gives an assessment of a physiological status in terms of reserve nutrition, which in general corresponds to the physiological age.…”

“…Physiological age has been successfully used in several studies to describe the physiological status of the individual Ixodes species (USPENSKY 1995). Although other methods of establishing a physiological parameter may be used, e.g., remaining fat or fertili-…”