Sample size (N = 6 per group) was based on the minimum number of individuals that would be allowed to observe the occurrence of rarer events (e.g., events that occur in approximately 5% of individuals) with reasonable probability based on a binomial assumption. The overall sample size of 18 would be sufficient to detect even rare events. A titration of mosquito bites (biting doses) was established; beginning with that arbitrarily considered the minimum number required causing an infection. Prepatent periods and duration of symptoms were expressed as geometric means. Differences among the groups were estimated by the Kruskal-Wallis test, and were considered statistically significant at P values less than 0.05.