New Evidence that Common Pesticide Kills Frogs

Tag : Pyridaben

A pesticide used to kill everything from head lice and fleas athome to agricultural pests in farm fields and mosquitoes inneighborhoods can decimate populations of frogs whose habitat isexposed to the poison, according to new research.
The pesticide, malathion , doesn't directly affect frogs, but repeated low doses leads tothe elimination of key links in the tad pole food chain,effectively destroying the ecosystem that supports leopard frogs,according to the University of Pittsburgh study, published in Ecological Applications and funded by the National Science Foundation. The zooplankton --tiny floating animals -- were killed, leaving their algae food togrow unfettered, which choked off so much light that it starvedbottom-dwelling algae that tadpoles eat. That, in turn, starved thetadpoles.
In the experiment, 43% of the leopard frog tadpoles in the exposedecosystem died, while wood frog tadpoles were not affected.
The experiment mirrored real-world conditions, in which thepesticide is applied in relatively small doses repeatedly overtime. Government regulations require only tests of toxicity tospecific species, not ecosystems, and they do not require testingon amphibians.
"The chain of events caused by malathion deprived a large fractionof the leopard frog tadpoles of the nutrients they needed tometamorphose into adult frogs," Relyea said. "Repeated applicationssustained that disruption of the tadpoles' food supply. So, evenconcentrations that cannot directly kill tadpoles can indirectlykill them in large numbers."
The results should be applicable to other pesticides, includingcarbaryl, diazinon, endosulfan, esfenvalerate, and pyridaben,according to Relyea.
The study is part of a nine-year project by Pitt researcher RickRelyea to determine whether pesticides are one cause of the globalamphibian decline. A previous study implicated the common weedkiller "Roundup" in frog deaths. The study is well-timed, since2008 is the Year of the Frog, an international effort to bringattention to the crisis.
That malathion is toxic is not news. Farm workers who hand-pickcrops must by law wait as long as six days after an application toenter fields, according to the Agency for Toxic Substances andDisease Registry. Like many pesticides, it is a man-made chemicalthat came into wide use in the 1950s and has remained in heavy usesince.