QUESTING BEHAVIOR OF IXODES-RICINUS TICKS (ACARI, IXODIDAE)

The vertical distribution in the vegetation of questing Ixodes ricinus ticks was investigated in two different vegetation types ('high' and 'low' vegetation) at two localities in south-central Sweden during 199 2-1993 (Toro) and 1995 (Bogesund). Significant correlations were found between the vertical distribution of immature ticks and the height of the vegetation. The greatest mean availabilities of the larvae and ny mphs in low vegetation were in the intervals 0-9 and 30-39 cm, respect ively. The larval numbers were greatest close to the ground (0-29 cm) in both high and low vegetation. The larval : nymphal ratio, at ground level at localities free of ground vegetation, varied between 8 : 1 a nd 32 : 1. In high vegetation, the greatest mean numbers of nymphal an d adult ticks were at height intervals of 50-59 and 60-79 cm, respecti vely. These ranges are within the estimated height interval (40-100 cm ) of the main part of the body surface of their 'preferred' host, the roe deer (Capreolus capreolus). The presence of most questing I. ricin us larvae at ground level would favour the transmission of Borrelia bu rgdorferi s.l., since this is where the highly reservoir-competent rod ents and shrews usually occur.