MECHANISMS OF INTERFERENCE COMPETITION IN THE WESTERN TREE-HOLE MOSQUITO, AEDES-SIERRENSIS

1. Mechanisms of interference competition affecting Aedes sierrensis (Ludlow) were investigated in laboratory microcosms using reconstituted, natural tree-hole detritus as food and substrate. 2. Pupation success, larval development time, and pupal weight were all affected by larval density but not by surface area:volume ratio of the microcosm. 3. Mature fourth instars affected pupation success, pupal weight, and development time of developing cohorts separated from them by a 2-mu-m pore membrane impermeable to bacteria, indicating that chemical competition is proportional to density of at least older instars. 4. Cannibalism does not occur, regardless of the presence or absence of food or physical complexity. 5. Fourth instars inhibited each other's feeding at densities of 64 larvae/ml or greater. Feeding inhibition due to physical contact (encounter competition) was abated but not eliminated by increasing physical complexity of the microcosm by the addition of leaves. 6. Levels of detritus and larval density both affect weight of day-1 fourth instars. Resistance to encounter competition is proportional to fourth instar weight and weight-specific resistance is correlated with rank weight within a developing cohort. 7. At densities around the population equilibrium in nature, encounter competition should be taking place, especially in tree holes with few leaves or other large litter.