Influence of Competition and Predation on Success of Cricotopus lebetis as a Biological Control Agent

The hydrilla tip mining midge, Cricotopus lebetis, has potential to control hydrilla, Hydrilla verticillata, an invasive aquatic weed. In this study, the influence on the midge of predation by the mosquitofish, Gambusia sp., and competition with the hydrilla leaf cutter moth, Paraponyx diminutalis, will be evaluated. The presence of these relationships in freshwater systems requires an understanding of how they can impact the success of the midge as a biological control agent. To study these relationships, combinations of the midge, moth, and fish were established in aquariums with hydrilla submersed in water enclosed by cages. The combinations tested were: midge; moth; midge and moth; midge and fish; and midge, moth, and fish. The control included only hydrilla and water to determine if damage occurs in the absence of the midge. The percent emergence of midges and moths, and hydrilla quality and quantity were assessed. Results of a preliminary study showed that predation by mosquitofish led to low midge emergence, but the moth had little impact on midge success. Further results will be discussed. This study will enable determination of the number of midge eggs that are required to overcome ecosystem interactions, and make a substantial impact on hydrilla growth.