Effects of diazinon on survival and growth of two amphibian larvae

Abstract

Amphibian populations are declining globally at an alarming rate and evidence suggests that pesticides may be a principal cause. The present study investigated the effects of diazinon on the survival and growth of larvae of two amphibians, Bufo melanostictus (Asian common toad) and the Sri Lankan endemic Polypedates cruciger (Common hourglass frog). Larvae were laboratory bred from egg clutches collected from ponds and wells in home gardens in the Gampaha and Colombo districts. Two separate trials were conducted using gill stage hatchlings (Gosner stages 20-22) of each species. The larvae were repeatedly exposed to 4 μg/L, 400 μg/L and 10 mg/L of diazinon for seven days. Results showed that exposure to 10 mg/L of diazinon caused significant elevations (p<0.05) in larval mortality in both B. melanostictus and P. cruciger as compared to the controls. No significant increases in mortality were noted at 4 μg/L and 400 μg/L. The trends in mortality were significant and positive for both species. Growth retardation was also noted at the highest dose of 10 mg/L, these larvae being significantly smaller than those in the controls (p<0.05). Larval activity was also seriously impaired at the highest dose.