Influence of competition and predation on survival of the hydrilla tip mining midge and its success as a potential augmentative biological control agent of hydrilla

Abstract

Hydrilla verticillata is an aquatic weed that grows densely throughout the water column and is costly to manage. The hydrilla tip mining midge, Cricotopus lebetis, a potential augmentative biological control agent of hydrilla, feeds on the apical meristem preventing growth. The goal of this study was to quantify the influence of a predator (mosquitofish, Gambusia sp.) and a competitor (hydrilla leafcutter moth, Parapoynx diminutalis) and their interactions, on the ability of the midge to survive and feed on hydrilla. The first experiment involved six treatments established in 37.8 L tanks with combinations of the organisms, including larval C. lebetis. Survival to adult midge eclosion was significantly reduced in the presence of the predator but was unaffected by the competitor’s presence alone. Apical meristem damage was reduced when both the competitor and predator were present. The second experiment included four treatments with C. lebetis egg masses or larvae and the presence or absence of mosquitofish. Adding C. lebetis as eggs rather than as larvae increased midge survival in the absence of the predator. Midge survival was lower when larvae were added, but the predator had no additional effect. To facilitate successful establishment of the midge and control of hydrilla, high numbers of larvae should be released to overcome predation.