Pesticides Research, 85 – Effects of Pesticides on Bombina bombina in Natural Pond Ecosystems

Effects of Pesticides on Bombina bombina in Natural Pond Ecosystems

7 Conclusion

Findings of pesticides decreased significantly with increasing width of buffer zone and there was found a tendency towards decreasing peak concentrations of pesticides with increasing width of buffer zone (1-10 m). In ponds with buffer zones wider than 5 m pesticide concentrations above 1,000 ng/l did not occur. Even buffer zones of 10 m width did not completely prevent contamination of ponds.

Hatching of eggs was almost 100 % successful and was apparently not influenced by pesticides. Young tadpoles (0-30 days old) was shown to be the most vulnerable life stage.

In 3 out of 8 cases there were a significant positive correlation between the Food Quality Index, representing the amount and quality of food sources for the tadpoles, and growth parameters of the tadpoles. This indicates that the quality and thickness of epiphytic coverings on stems of higher plants are probably of vital importance for the fitness of the tadpoles of Bombina bombina.

Only in one case an indirect negative effect of pesticides on tadpoles was found. Probably because of contamination with herbicides, the higher plants in a pond was wiped out in 1995 and replaced by dense mats of filamentous algae, causing very poor survival of both newly hatched and large tadpoles.

A few significant correlations between growth parameters of tadpoles and pesticide contamination was found, but the results were contradictory. At least some of the correlations must have been coincidental due to a low number of ponds investigated.

Synergistic and additive effects on tadpoles of commonly used insecticides and fungicides at repeated exposures to low concentrations is recommended to receive more attention in future studies.

Intensive cultivation can possibly reduce the yearly survival of adult frogs. Adult survival of 80-94 % was found on more natural habitats and 55-60 % in the most cultivated areas. Lower adult survival in cultivated areas are suspected to be caused by mechanical disturbance by heavy machinery and the use of fertilizers and pesticides.