The results support the hypothesis that infected monarchs would travel shorter distances, and that among infected individuals shorter distances are correlated with higher parasite loads. The researchers suggest that infected butterflies from more northern locations were not able to reach their wintering grounds in Mexico, thus backing the "migratory culling" idea of reducing parasites among a population by removing infected individuals. Since there was no significant effect of latitude on the odds of infection, the researchers propose that the flight performance of monarch butteflies has a greater effect on the chances of reaching their wintering grounds than the incidence of parasite transmission among populations.
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