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In search of fluctuating asymmetry: no evidence among Chironomus tentans (Diptera: Chironomidae) parasitized by the ectoparasitic water mite Unionicola foili (Acari: Unionicolidae)

Edwards, D.D.

2004 - Volume: 44 Issue: 3-4 pages: 209-217


A positive relationship between parasitism and fluctuating asymmetry (FA) is well documented in the parasitological literature. Hosts with higher levels of FA may be more susceptible to parasitism. Alternatively, parasites can increase FA of hosts through their effects on developmental stability. The present study examines the relationship between parasitism by the aquatic mite Unionicola foili (Edwards and Vidrine) and FA in their host midge Chironomus tentans (Fabricius). An examination of wing asymmetry among parasitized and unparasitized midges did not reveal a positive association between wing FA and infection. These results are consistent with behavioral experiments indicating that larval mites do not appear to influence the developmental stability of chironomid hosts during colonization. These data also coincide with previous studies indicating that larval U. foili do not have a negative influence on fitness components of C. tentans. Other studies of FA and parasitism involving mites and midges have suggested that mites discriminate among potential hosts and use some correlate of FA when choosing a host. However, data from experiments presented in this study revealed that the number of mites rejected by insects was not significantly different, whether mite larvae were presented with one host or a choice of two host pupae. These data suggest that midges are not under strong selection to reject larval mites. In addition, mite larvae are not expected to be under strong selection to preferentially colonize more suitable hosts.

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2004 Edwards, D.D.
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