Effects of the facultative predator Anopheles barberi on population performance of its prey Aedes triseriatus (Diptera culicidae)

We tested the hypothesis that predation by Anopheles barberi (Coquillett) on young larvae of Aedes triseriatus (Say) reduces intraspecific competition among surviving prey and thereby increases survival, mass at eclosion, and estimated rate of population increase, or decreases development time for A. triseriatus. In a field experiment manipulating both litter (=food) abundance and predator abundance, total survivorship of A. triseriatus was significantly reduced by A. barberi predation in tree holes, but not in tires where overall survival was extremely low. Survival to adulthood and estimated finite rate of increase (λ′) were significantly lower in low-food treatments, but were unaffected by the predator. Days to and mass at eclosion were unaffected by predation. This field experiment thus provided no evidence for a positive effect of predation by A. barberi on A. triseriatus population performance. A laboratory functional response experiment yielded no asymptotic saturation of number of prey killed by A. barberi of any instar. Fourth-instar A. barberi feeding on either 1st- or 2nd-instar A. triseriatus had indistinguishable functional responses, but 3rd-instar A. barberi killed significantly fewer 1st-instar prey than did 4th-instar A. barberi, and did not kill 2nd-instar prey. Censuses of tree holes and tires showed limited seasonal co-occurrence of predator-prey instar combinations that can lead to predation. These data suggest that A. barberi has only a limited potential to reduce populations of A. triseriatus and that such effects are likely only during a short period in midsummer.