The control of Chironomid larvae in ponds, using TDE (DDD).
Abstract
The following is based partly on the authors' summary. Preliminary laboratory tests with larvae of Chironomus riparius Mg., Asellus aquaticus (L.), Tubificids (Annelid worms) and rainbow trout suggested that wettable-powder formulations of DDD and DDT at more than 0.5 Ib. toxicant per acre would give effective control of the Chironomids without killing the trout either directly or through ingestion of treated larvae. Mortality of Asellus was also heavy, but Tubificids were not killed with application rates as high as 2 Ib. per acre. DDD was considered preferable to DDT because it was less toxic to fish. In field studies of the effect of a single treatment on the fauna of a eutrophic pond in south-eastern England, DDD was applied at 1 Ib. per acre in January 1962, after a period of observation. A comparison between the treated pond and a neighbouring untreated one, using data obtained from emergence cages, plankton sweeps and mud-core borings, showed that species and numbers of mud-dwelling Chironomid larvae were greatly reduced by the treatment and that Chaoborids and Ephemeroptera were also killed. Few Chironomids were present in March 1963. No effect on other benthic or planktonic organisms, which included some mosquitos, was discerned. There was 35 per cent. mortality from unknown causes among carp kept in cages in the pond for 11 months following treatment, but the survivors grew well. Fish tissues examined in November contained about 15 parts DDD per million. After spraying, DDD concentrations in the water fell from 0.033 to 0.001 p.p.m. (the analytical limit of sensitivity) in two weeks, and those in the mud fell from 1 to 0.12 Ib. per acre in about ten months.