The Effects Of Pesticides On Wildlife
Pesticides affect a broad range of species in a wide variety
of ways. Effects can be immediate and lethal, or long-term and sub lethal.
Pesticides can act directly, by poisoning, by affecting the hormone system, and
so on, or indirectly, by altering a species' habitat or food supply. While the
first casualties will be those species in the immediate area where the
pesticides were applied, such as beneficial insects, the effects will not
necessarily end there.
Pesticides move in the environment, and often persist
over long periods of time, and therefore species outside of the targeted area
will be affected. Some of the key species we need to worry about are bees,
birds, amphibians, and fish.
Bees are very important insects because they act as pollinators, which is
important for biodiversity and for agricultural production. Bees recover slowly
from insecticide spraying and other disturbances because of their low fecundity
(they are unable to reproduce rapidly or in great numbers) which also makes
them more susceptible to local extinction.
For more information on pesticides and bees try these websites:
In Canada, more than 30 registered pesticides can poison wild birds. Most of
these are the cholinesterase-inhibiting organophosphates and carbamates.
Mammals are much better than birds at detoxifying organophosphates and
carbamates. For example, birds are 100 times more sensitive than mammals to the
organophosphate diazinon, a common active ingredient in many insect sprays.
Insects and vegetation sprayed with insecticides can contain sufficient
residues to kill birds. Sublethal effects can also occur, as well as such
indirect effects as habitat loss and the depletion of food supplies.
For more information on the impacts of pesticides on birds, try these websites:
There is growing evidence that pesticides are partly responsible for dramatic
amphibian population declines occurring throughout North America. The
consequences of chemical stressors, such as pesticides, on amphibians are
lethal, sublethal, direct and indirect. The sublethal affects include hampered
growth and developmental and behavioral abnormalities. In turn these
abnormalities may increase an amphibian's susceptibility to predation and
decrease its reproductive success.
Pesticides also weaken the immune system
making amphibians more susceptible to parasites, disease and UV radiation.
Certain pesticides can disrupt the endocrine system, resulting in sexual
malformations, such as hermaphroditism (see section on Endocrine Disruption).
For more information on amphibians and pesticides see:
The US Geological Service has found concentrations of pesticides in Pacific
Northwest rivers and streams at levels that are associated with negative
impacts on fish growth, development, behaviour and reproduction. Pesticides can
impair swimming ability, cause abnormal sexual development, and cause skeletal
deformities. Indirect affects include reduction in food supply, and reduction
or elimination of vegetative cover used by young fish. In BC, and the entire
Pacific Northwest, the main concern is for the health of already greatly
depleted salmon stocks.
For more information on pesticides and fish see: