Effects of carbofuran on survival and growth of Duttaphrynus melanostictus tadpoles

Abstract

This study investigated the impact of a commonly used carbamate pesticide, carbofuran, on survival, growth, development and activity of larvae of the Asian Common Toad, Duttaphrynus melanostictus Schneider 1999. Continuous exposure trials of 15 days were conducted using tadpoles of Gosner stages 24-25 with a commercial grade carbofuran (Curaterr 3G). Four concentrations 50, 150, 250 and 500 ?gl-1 were tested and treatments and controls (without pesticides) were maintained in triplicate (n=56 per treatment or control). Results revealed that there were marked elevations in mortality in larvae exposed to all tested concentrations as compared to those in the controls. Mortality was, however, not dose-dependent, but depicted a hermetic response, where mortality at 500 ?gl-1(35 %) was much lower than that recorded at 250 ?gl-1 (62 %). The 15day LC50 value of D. melanostictus larvae was 190 ?gl- 1. In contrast to mortality, the effects on growth, development and activity although pronounced, were  transient. For instance growth impairments were noted until day 7, but the body size of surviving tadpoles were comparable to those in the controls by the end of the trial. Exposure to carbofuran to concentrations of 150 ?gl-1 and above also caused several notable morphological aberrations such as swollen heads and thin tails. In particular, the fact that carbofuran induced high levels of mortality at the tested concentrations, which are below the field application levels, suggest that this pesticide may be detrimental to the survival of amphibians inhabiting agricultural landscapes in Sri Lanka.