Colonization and development of insects in simulated treehole habitats with distinct resource and pH regimes

Abstract

I used replicated artificial treehole habitats to determine how initial colonization and subsequent growth of treehole insect larvae were affected by water volume, leaf litter mass, and pH. Low leaf litter mass had the most significant and recurring effect on the communities. Densities of the common insects, Aedes triseriatus (Say), Culicoides guttipennis (Coquillett), and two scirtid beetle species (Helodes pulchella [Guerin] and Prionocyphon discoideus [Say]) were all higher in low leaf mass than high leaf mass microcosms. Species richness early in the experiment was higher in high water volume and low leaf resource microcosms, suggesting earlier colonization in those microcosms. Growth and survival of C. guttipennis and the syrphid Mallota posticata (Fabricius) were adversely affected by low pH. More scirtid beetles were attracted to low leaf mass habitats, yet scirtids grew to a larger size in high leaf litter treatments. This suggests that oviposition preferences of females, intraspecific competition of larvae, and amount of resources all may affect larval growth rates. All three factors, water volume, leaf mass and pH, affect community composition in treeholes through effects on habitat preference, larval growth, and survival. Treehole communities in Pennsylvania are thus affected by heterogeneity in space and resources, and water chemistry factors.