Opportunistic response of a benthic midge (Diptera: Chironomidae) to management of California seasonal wetlands.

The effects of seasonal flooding on larvae of Chironomus stigmaterus Say were studied in 12 managed wetlands of the Sacramento-San Joaquin River estuary, California. Six pairs of wetlands were flooded artificially on 5 and 19 August; 2, 16, and 30 September; or 14 October 1991. One member of each wetland pair was dominated by pickleweed, Salicornia virginica L., and the other by alkali bulrush, Scirpus robustus Pursh. Densities of midge larvae were significantly higher in wetlands flooded earlier than later. The numerical patterns exhibited by C. stigmaterus populations suggest opportunistic responses. Midges thrived in habitats 1st flooded in August, yet such habitats would not naturally exist in the California Mediterranean climate because the rainy season does not begin until late autumn. Although this midge probably evolved in freshwater habitats, it readily colonized habitats dominated by pickleweed, a salt march plant. Populations of the beetle Berosus ingeminatus d'Orchymont also were higher in pickleweed wetlands during autumn. Because C. stigmaterus larvae are an important food resource for dabbling ducks, their opportunistic response to the artificial conditions in California seasonal wetlands has benefits in terms of waterfowl management.