DIFFERENCES IN ATTACHMENT OF WATER MITES ON WATER BOATMEN - FURTHER EVIDENCE OF DIFFERENTIAL PARASITISM AND POSSIBLE EXCLUSION OF A HOST FROM PART OF ITS POTENTIAL RANGE

This paper is the latest study on the distribution of two sympatric sp ecies of water boatmen in saline lakes in British Columbia. It is a fu rther examination of a study by Smith, who found that parasitic water mites have higher prevalence and abundance on Cenocorixa expleta than on C. bifida. He hypothesized that this is one of the main factors res ponsible for the small populations of C. expleta in lakes below 13000 mu S.cm(-1). We performed laboratory experiments with the mite Eylais euryhalina on two different wing morphs of the two host species. Over 8 days, we found higher prevalence and abundance of mites on the predo minant, flight-incapable morph of C. expleta than on the predominant, flight-capable morph of C, bifida. Eylais euryhalina attached over mos t of the abdominal terga of C. expleta, but generally attached only to the permanently non-sclerotized thoracico-abdominal membrane of C. bi fida. Infecting both wing morphs of bath species showed that locations of mite attachment differed according to the wing morph and the assoc iated differences in sclerotization, whereas the effect of species was equivocal. We hypothesize that a factor in C. expleta's exclusion is the greater potential mite-attachment area of its predominant, unscler otized morph.