Abstract:
Amphibiati populations arc declining globally at an
alaiming rate and a growing body of evidence suggests thai
pesticides may be a major cause. The present study is aimed
at providing empirical evidence for the potential impact of
pesticides on amphibian populations. The effects of diazinon.
a widely used organophosphate pesticide, on the survival and
growth of larvae of two amphibians, the common toad Bujb
inelanoslicius and the Sri Lankan endemic common hourglass
frog Polypadates cruciger are investigated.
Larvae were laboratory bred from six egg clutches, three
from each species, collected from ponds and wells located in
home gardens in Delgoda and Malabe in the two districts of
Gampaha and Colombo. Two separate trials were conducted
using gill stage hatchlings{Gosner stages 20-22) of each species.
The larvae were held in glass tanks and repeatedly exposed
to 4 ug/L, 400 ug/L and 10 mg/L o f diazinon for seven days.
Larval mortality was recorded daily, whilst the body length and
activity levels were measured at the end of the experiment.
Results showed that exposure lo 10 mg/L of diazinon
caused significant elevations (p<0.05) in lar\'al mortality
in both B, melanostictus and P. cruciger as compared to the
controls. On the other hand, no significant increases in mortality
were noted at 4 and 400 ug/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 Ihc controls (p<0,05).
Larval activity was also seriously impaired at the highest
dose. This study is one of the initial studies that have provided
empirical evidence of the harmful etTects of pesticides on larval
mortality, groulh and activity of native amphibian species in
Sn Lanka. In view of these findings, we suggest that pesticides
may facilitate the decline of"many amphibian populations in Sri
Lanka.
