The effects of DDT, when used as a mosquito larvicide, on tadpoles of the frog Rana temporaria

Abstract

Several water bodies on the Isle of Grain in North Kent have been sprayed annually with DDT by the local Health Department to control mosquito larvae. In 1971 the effects of this treatment on caged tadpoles ( Rana temporaria) were assessed. Two nylon mesh cages were staked in each of five different water bodies varying in size from a ditch 1 m wide to a gravel pit 140 × 30 m. Tadpoles were placed in the cages four or five days before spraying. In the vicinity of the cages, the margins of each site were sprayed with 0·4–0·5 kg DDT/ha. Observations were made and tadpole samples were taken for analysis one, three and fourteen days after spraying. Death, morphological abnormality or hyperactivity occurred only amongst tadpoles in the three smallest sites. Tadpoles in most of the cages were exposed to DDT for many days after spraying. In a site where tadpoles were exposed to high acute levels, larval development was significantly retarded, whilst, in the largest site, where tadpoles acquired tissue residues more slowly, their rate of metamorphosis was increased. These observations were consistent with those made during acute and chronic dosing experiments in the laboratory and further similarities between field and laboratory studies are discussed. The effects of this use of DDT on tadpole populations is briefly considered. Residues in free-living snails and fish were also determined.