Field evidence for aggregating behaviour in the tick Ixodes ricinus L.
2004 - Volume: 44 Issue: 1-2 pages: 3-14
KeywordsIxodes ricinus questing clump clumping aggregation pheromone
The relative spatial micro-distribution of questing adult Ixodes ricinus ticks was determined by observation and counting of occurrences on stems of the rush Juncus effusus in deer-inhabited oak woods in Killarney in south-west Ireland. Overall, a total of 2077 individual ticks were counted during observation of an estimated 200,000+ rush stems. Analysis of data demonstrated significantly more females than males in the population sample. The distribution of the frequency classes for single ticks, pairs, triplets, etc. was found to be significantly clumped and a negative binomial distribution provided a good fit to the observed distribution. Among observed pairs of ticks, a significant excess of female-male pairs was found as well as corresponding deficits of female-female and male-male co-occurrences compared with expected numbers based solely on the observed proportions of males and females. In addition, separate statistical analysis of female and male data showed that the distributions for each sex were also clumped when the female-male aggregating factor was removed from the data. Overall, the results demonstrate widespread fine-scale aggregation of questing ticks and it is concluded that this is likely to be pheromone-mediated. The results indicate the action of a sex-attractant as well as an assembly attractant while the role of other pheromones is not precluded.
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