INFESTATION OF MAMMALS BY IXODES-RICINUS TICKS (ACARI, IXODIDAE) IN SOUTH-CENTRAL SWEDEN

Infestation by Ixodes ricinus ticks on rodents, hares and cervids was examined at Bogesund, 10 km north of Stockholm, in south-central Swede n during 1991-1994 and on varying hares (Lepus timidus) at Stora Karls o and Gotska Sandon in the Baltic Sea during 1992-1993. At Bogesund, t here were great differences between two consecutive years in the numbe r of I. ricinus larvae infesting bank voles (Clethrionomys glareolus). The seasonal pattern of infestation by I. ricinus larvae and nymphs o n bank voles was unimodal in 1991, with peaks in June-July and bimodal in 1992, with peaks in June and August. Male bank voles, compared to females and older voles, compared to young voles, harboured greater nu mbers of I. ricinus ticks. Apodemus mice, compared to bank voles, harb oured greater numbers of I. ricinus ticks. Ixodes ricinus larvae engor ged on Apodemus mice were heavier than larvae engorged on bank voles a nd resulted in larger nymphs. However, there was no difference in the proportions of viable nymphs resulting from larvae engorged on mice or voles. The ranges in the numbers of I. ricinus ticks infesting indivi dual hosts were 1-451 for rodents, 16-2374 for hares and 428-2072 for roe deer (Capreolus capreolus). These ranges of tick numbers are estim ated to represent potential blood losses from individual hosts of appr oximately 0.2-65% for rodents, 0.2-13% for hares and 0.3-9.0% for roe deer. Within the populations of all host species examined, the distrib utions of all stages of I. ricinus were clumped, with most host indivi duals harbouring few ticks and only a few individuals harbouring many ticks. The data suggest that, even though a small proportion of tick h osts may be severely affected, the direct effects of feeding by I. ric inus are unlikely to play an important role on mammal population dynam ics.