Improving hydrilla biological control via the hydrilla midge tip miner.

The invasive aquatic weed, Hydrilla verticillata, was introduced into Florida in the 1950s and has since invaded watersheds statewide. Hydrilla produces surface mats, which clog waterways, prevent sunlight penetration into the water, and displace native plants. Herbicide resistance has been recorded in hydrilla, emphasizing the importance of alternative management strategies such as biocontrol. The herbivorous midge, Cricotopus lebetis, has been identified as a potential biocontrol agent. As a larva, the midge mines into hydrilla’s apical meristem, which changes the plant’s architecture by preventing further vertical growth, thus restricting surface mats. The midge has been collected and colony reared to augment existing populations. However, rearing protocols have not been evaluated to determine their impact on colony production. It is therefore important to assess these protocols to optimize mass rearing success. Experiments have investigated the effects of (a) cold storage on development; (b) the biorational species-specific Btk for lepidoptertan colony pests; (c) intra-specific and (d) inter-specific competition. Midge egg hatch is significantly decreased after 7 days and adult emergence after just 2 days of cold storage. A concentration of 0.2 and 2.0 mL Btk/gallon water effectively reduces pests without harm to the midge colony. More than one larva per hydrilla tip induces intra-specific competition and does not increase adult numbers. Inter-specific competition with fish reduces midge emergence more than competition between the midge and moth or the midge alone.  By improving mass rearing of C. lebetis via methods development studies, an IPM program can be better implemented for sustainable control of hydrilla.