Report from the Sub-comittee on the environment and health

Exposure of field fauna
through treatment with
insecticides
Direct effects on natural
enemies of pests in fields
treated with pesticides
5.1 Impact of pesticides on <strong>the</strong> fauna in cultivated and
uncultivated terrestrial ecosystems
The environmental impact <strong>from</strong> <strong>the</strong> use of pesticides, understood as <strong>the</strong>
effect on flora and fauna in farmland and forests is closely connected
with how <strong>the</strong> individual pesticide is used and how often it is applied, <strong>the</strong>
pesticide’s fate in <strong>the</strong> environment and its toxic properties. The impact
on <strong>the</strong> individual plant or animal species depends on <strong>the</strong> species’
dispersal in time and space, how sensitive <strong>the</strong> species is to a given
pesticide (direct effects) and how affected it is by changes in <strong>the</strong>
population of o<strong>the</strong>r species and o<strong>the</strong>r indirect effects. The effect of
pesticides must also be seen in relation to o<strong>the</strong>r factors that affect
farmland fauna – particularly fertilisation, soil treatment, crop rotation
and o<strong>the</strong>r operational measures. In addition, reduced dosages, split
dosages and product mixtures affect <strong>the</strong> pesticides’ impact on <strong>the</strong> fauna
directly or indirectly through <strong>the</strong>ir effect on <strong>the</strong> flora. The information in
this section is amplified in Elmegaard (1998) and Strandberg (1998).
The exposure of <strong>the</strong> fauna in cultivated fields depends in part on how <strong>the</strong>
products are applied. There are three common methods in Denmark:
spraying with a boom-spray, spreading on <strong>the</strong> soil as granulate and
dressing of seed. Spraying is far and away <strong>the</strong> most common method.
Insecticide applied with a boom-spray is normally placed in a developed
crop with some degree of cover. The insecticide is deposited in small
drops of water on <strong>the</strong> leaves and stems down through <strong>the</strong> crop, and <strong>the</strong>
remainder lands on <strong>the</strong> ground. When cereal crops are sprayed with
insecticide, 10-30% of <strong>the</strong> insecticide normally ends up on <strong>the</strong> ground.
Deposition is greatest at <strong>the</strong> top of <strong>the</strong> crop, close to <strong>the</strong> nozzles, and
decreases on <strong>the</strong> way down through <strong>the</strong> crop. For animals living up in <strong>the</strong>
vegetation, exposure can also take place as <strong>the</strong>y come and go on
contaminated leaf surfaces (residual uptake) or via <strong>the</strong>ir food, which is
ei<strong>the</strong>r parts of plants or o<strong>the</strong>r arthropods.
For species that live on or in <strong>the</strong> soil, <strong>the</strong>re can similarly be several
exposure routes. The effect of <strong>the</strong> substance deposited on <strong>the</strong> ground
depends on how strongly <strong>the</strong> substance adsorbs to organic matter and soil
particles and thus also on <strong>the</strong> composition of <strong>the</strong> soil. Many insecticides
adsorb strongly to clay or organic matter and <strong>the</strong>refore have low
bioavailability in soil.
Beneficial animals, meaning <strong>the</strong> natural enemies of pests, can be divided
into two groups: general and specific predators. General predators live
<strong>from</strong> many kinds of food and <strong>the</strong> most important species are to be found
among ground beetles, rove beetles and spiders. The main species seek
food on <strong>the</strong> surface of <strong>the</strong> ground and, in <strong>the</strong> case of some species of
spider, by means of webs in <strong>the</strong> vegetation. The o<strong>the</strong>r group of beneficial
animals is specific predators, which live mainly or only <strong>from</strong> a limited
group of pests. In cereals, aphids are <strong>the</strong> main pests, and <strong>the</strong> specific
predators are ladybirds, parasitic wasps, buzzing fly larvae and lacewing
larvae.
In <strong>the</strong> case of boom spraying, direct toxic effects on field arthropods are
caused mainly by insecticides, although herbicides and fungicides can
also have direct toxic effects on some arthropods. The pest is often an
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