Is infestation the result of adaptive choice behaviour by the parasite? A study of mites and midges

We studied the possibility that a parasite, a hydracharinid mite, chooses its host, a chironomid midge. Mites, Unionicola ypsilophora, were placed into containers with either one or two Chironomus plumosus pupae and we counted the number of mites on the midges after the latter had emerged. Fewer mites were rejected by hosts when they had a choice of host, suggesting that they actively choose which individual to parasitize. In several midge species collected in the wild, fluctuating asymmetry in wing length was a good predictor of mite infestation. We suggest that mites use some correlate of fluctuating asymmetry to make their choice of host.