Methodology for sampling questing nymphs of Ixodes ricinus (Acari : Ixodidae), the principal vector of lyme disease in Europe

To assess the Lyme borreliosis vector population density we set up a method ology for sampling the Ixodes ricinus L. population host questing on the ve getation. We focused on the collection of the nymphal stage, which is the p rincipal stage of disease transmission to humans. This study was carried ou t in Rambouillet forest (Yvelines, France) where seven study areas were dem arcated. These areas are maximally homogeneous for plant species using a fi ner scale than the phytosociological classification as defined by the metho d of landscape diagnostics. Out of 23 collections performed from March 1997 to May 1998, 2,906 I, ricinus nymphs were collected. The sampling techniqu e chosen was the cloth lure technique. The technical parameters were studie d and fixed (cloth type, cloth size, sample size, researcher position). It appeared that toweling was the best cloth type to optimize the number of ti cks collected; the position of the researcher had no effect on tick samples . To satisfy the criteria for correct sampling, we studied representativity , randomness, and nonselectivity of our methodology. The spatial distributi on of nymphs in a homogeneous area was close to random and thus very few su bsamples were needed to obtain a relative density which was representative. No significant differences were found between random samples and following transect samples; and nonselectivity was totally satisfied because we only worked on questing nymphs. We grouped the samples that presented no signif icant differences to attribute a density index, which varied fr om 0 to 5. This methodology, applied with the same parameters, offers potential for pr oducing comparable results from studies in different geographical areas and at different times of the years.