Impact of - IDL-BNC @ IDRC - International Development Research ...

and gypsum) are preferable to more resilient particles (e.g., silica and corn
cob). Also, not all available granular products have been included in this table.
Based on this information, the safest product is not an organophosphate or
carbamate, but rather a pyrethroid. Provided that pyrethroid insecticides can
be kept out of aquatic systems, they should be used in preference to organophosphates
or carbamates. They usually provide a large margin of safety for
terrestrial vertebrates and are, therefore, ideal for granular formulations.
Seed dressings
Seed dressings or seedcoats, whether factory applied or added to the seed just
before planting, constitute another well-known wildlife hazard. Many species
are naturally attracted to seeds. Awareness of the hazard first came to light
following massive kills of birds by organochlorine and organomercurial seed
dressings used in North America and Europe. The offending organochlorines
were mainly aldrin, dieldrin, and heptachlor. In contrast, one organochlorine,
lindane (y-benzene hexachioride, BHC), appears to be safe for wildlife and is
currently the material of choice for cereal treatments in Canada. Lindane does
not seem to accumulate in wildlife tissue to any degree, although it does give
rise to some contamination of the environment by assorted BHCs that are
either present as impurities or metabolized from the gamma isomer. This
product is currently thought to be preferable to the more toxic organophosphate
or carbamate alternatives, which have been linked to wildlife kills
(Greig-Smith 1988) in such products as carbophenothion and
chlorfenvinphos.
Contaminated insects or other prey
Spraying of an insecticide often results in a local abundance of food in the form
of dead or moribund insects, either of the pest species or of assorted nontarget
species. A number of bird species make use of this temporary bounty and will
gorge themselves, often to their detriment. For example, California Gulls
(Larus californicus) died from ingesting lethal quantities of grasshoppers
sprayed with a liquid formulation of carbofuran (Leighton 1988). Crackles
(Quiscalus quiscula) have been killed under the same conditions. Carbofuran
has also been shown to have a dramatic impact on a rare ground-nesting owl
species in Canada, the Burrowing Owl (Athene cunicularia) (Fox et al. 1989).
The owls are probably poisoned as they feed on contaminated grasshoppers,
although they may also be exposed through ingesting surface-coated small
mammals. The liquid formulation of carbofuran is under regulatory reevaluation
in Canada.
Forestry insecticides
In contrast to cultivated field situations, pesticides are applied directly to
complex wildlife habitats in forested areas, where a large number of individuals
of many species can be exposed. For this reason, forestry products must
251