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The infections of emerging damselfly cohorts by ectoparasitic water mites Arrenurus cuspidator were followed closely over two years in two populations. In one pond Coenagrion puella was the single host species, whereas in the second pond C. hastulatum co-occurred. The prevalences found were close to 100%. The mean daily abundance of mites ranged from I to 45 mites per host with a peak after roughly one third of the emergence period.

The water mites displayed a clumped distribution on their hosts measured by the variance/mean ratio. No differences in parasite abundance due to host sex, head width, or host species could be detected. The abundance of mites was synchronised with host's emergence patterns. This was stronger in the system with two host species. Shaw and Dobson recently showed a generalised relationship of variance/mean of parasite abundance combining data from 269 host parasite systems. The data presented here and some other water mite associations show a significant deviation from this general rule.