Effects of carbaryl on the spring zooplankton communities in ponds.

A carbamate insecticide, carbaryl, was applied in spring to concrete ponds to study its effects on zooplankton communities. The population density of Cladocera (Daphnia spp.) was nearly constant before application of the chemical. Carbaryl at 1 ppm killed all zooplankton species, including Chaoborus larvae. After treatment, cladocerans never recovered to their previous level. The relatively rapid recovery of a predator, Chaoborus, seemed to interfere with recovery of the cladoceran populations. The lower water temperature occurring in spring was thought to favour the former because of its influence on growth rates.