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Biological Sciences


Steven Juliano

Mentor Department

Biological Sciences


The dilution effect hypothesis postulates that greater biodiversity of potential hosts can reduce parasite prevalence and abundance. Encounter reduction could occur if invasive species, or noncompetent hosts, remove parasites from the environment and reduce infections of competent hosts. An alternative mechanism is host-host competition which may occur if invasives compete with the native host, reducing its resource acquisition and its ability to support parasites. Alternatively, host-host competition may amplify infection if competition reduces host immune defenses. We tested for the dilution effect, and the possible mechanisms, using the North American tree hole mosquito Aedes triseriatus and its protozoan parasite Ascogregarina barretti, with Aedes albopictus as the invasive species. We collected contents of 6 water-filled tree holes from a site where A. triseriatus and A. barretti are abundant. In the lab, we removed resident larvae and halved water and sediment of each tree hole. Both halves received a standard number of 1st instar A. triseriatus larvae. One of the halves was a control, while the other received the same number of 1st instar A. albopictus larvae. We dissected A. triseriatus 4th instar larvae and pupae from each treatment/tree hole. ANOVA revealed no significant effects of treatment (control, albopictus) on infection for both A. triseriatus larvae and pupae. These results do not demonstrate dilution. Means for parasite numbers in both larvae and pupae are lower in the albopictus treatment than in the control treatment. This trend suggests that an experiment using more tree holes may be a useful follow-up to this study

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