Prior occupation by scirtid beetles does not affect mosquito and midge populations in treeholes
The primary resource of temperate forest treeholes is leaf litter, which exists along a continuum of decay states, with different insects specializing on particular states. Scirtid beetles (Helodes pulchella) take part in a processing chain interaction by shredding and processing leaf litter, thereby creating material for consumption by other detritivores. Variation in scirtid density and resource availability could thereby influence the distribution of resources and thus the abundance of the dominant eastern treehole mosquito Aedes triseriatus. In addition, pupated or dead scirtid beetles typically leave behind processed or semi-processed leaf litter, particularly if the numbers of beetles is large, which potentially impacts insect communities after the beetles are gone. We tested the hypothesis that prior presence of scirtids has observable effects on the abundance of treehole mosquito populations. We used a two-factor fully crossed design (3 leaf litter levels x 3 scirtid densities) with 4 replicate mesocosms per treatment to monitor larval insect abundance from April 2004 to June 2005. Scirtids did not persist in mesocosms to the first census of 2005. Abundance of A. triseriatus was unaffected in 2005 by either initial scirtid density or leaf litter availability. In addition, we detected no statistically significant effects of scirtids on the rate of leaf litter decay.