EDWARDS, D.D.: Increased fluctuating asymmetry among chironomid midges in repsonse to ectoparasitic water mites: implications for fluctuating asymmetry theory.
The larvae of most species of water mites must undergo a brief parasitic phase with insects to complete their life cycle. Several studies have found a significant correlation between mite load and the degree of fluctuating asymmetry (FA) host characters, suggesting that mites increase FA through their effect on developmental stability. To date, FA primarily has been reported among hemimetabolous insects that become infested during pupal ontogeny. Holometabolous insects that are parasitized by mites when they are adults are not expected to exhibit FA because they are infested once they have completed development. Parasitic associations between the water mite Unionicola foili and the holometabolous midge Chironomus tentans were established in the laboratory and revealed that FA of forewing length was significantly greater in infected than in uninfected midges. These results are inconsistent with the initial prediction, suggesting there are other mechanisms by which larval mites may affect FA of host midges. Behavioral observations revealed that the presence of mite larvae induced an increase in antiparasitic behavior by pupal C. tentans. Because antiparasitic behavior id assumed to be extremely time consuming and energetically expensive, it may be expected to have an affect on the developmental stability of midges and thus increase the degree of FA.