Report from the Sub-comittee on the environment and health

Importance of headland
vegetation to <strong>the</strong> fauna
Effect of pattern of pesticide
use on flora and fauna
indirect, since herbicides and fungicides remove <strong>the</strong> food eaten by <strong>the</strong>se
insect groups (Hald et al. 1994; Reddersen et al. 1998).
The absence of herbicides, in particular, plays a major ecological role in
headlands because it results in a much richer flora, with <strong>the</strong> possibility of
both flowering and seeding. The ground cover with different plant
species is important as a food resource for herbivores, insects that visit
flowers and seed-eaters, although <strong>the</strong> microclimate and <strong>the</strong> possibility of
concealment also play a role (Reddersen et al. 1998). Buffer zones
bordering on uncultivated small biotopes also mean that ground beetles
and rove beetles can overwinter <strong>the</strong>re and return to <strong>the</strong> field in <strong>the</strong> spring.
Certain common insect groups occur in <strong>the</strong> field only in <strong>the</strong> buffer zone
along uncultivated small biotopes, whe<strong>the</strong>r, as in <strong>the</strong> case of plant bugs
and plant hoppers, <strong>the</strong>y live <strong>the</strong>re or, as in <strong>the</strong> case of harvest spiders,
ants and woodlouse, <strong>the</strong>y are simply guests <strong>from</strong> <strong>the</strong> boundary biotope.
Only a few species of bird and small mammal live in <strong>the</strong> cultivated field,
while <strong>the</strong> many species living in uncultivated small biotopes often go on
foraging excursions in <strong>the</strong> field edge: that applies, for example, to
different species of mice and species of bird, such as yellowhammer,
partridge and pheasant. Such species naturally potentially benefit <strong>from</strong>
<strong>the</strong> ample food resources available to <strong>the</strong>m in unsprayed headlands.
Wild plants are an important and basic element in <strong>the</strong> agroecosystem’s
species diversity, see earlier sections. Use of reduced herbicide dosages
could be expected on average to leave more weed in Danish fields.
Surviving plants could form a food resource for herbivorous insects,
among o<strong>the</strong>rs, if <strong>the</strong> food quality of <strong>the</strong> host plants were adequate. This
has been studied in <strong>the</strong> case of <strong>the</strong> knotgrass leaf beetle and <strong>the</strong> herbicide
Glean (Elmegaard, Kjær 1995; Kjær, Elmegaard 1996).
There is generally reason to assume that sublethally treated plants can
form a food resource for herbivorous animals. The treated plants do not
always have <strong>the</strong> same quality as untreated plants, but for herbivorous
animals and seed-eaters, insects visiting flowers, etc. a little food is better
than none.
However, <strong>the</strong>re has not been any clear tendency towards an increase in
<strong>the</strong> amount of weed due to <strong>the</strong> widespread use of reduced dosages – at
any rate not when <strong>the</strong> registration takes place at harvest time (Kristensen
1994). In o<strong>the</strong>r words, farmers have become better at spraying optimally
and are achieving <strong>the</strong> same effect with reduced dosages. Studies have not
been carried out of <strong>the</strong> development of weed throughout <strong>the</strong> season as a
function of changes in <strong>the</strong> spraying pattern.
Reduced dosages of insecticides are not widely used, but are
recommended in certain cases by <strong>the</strong> Agricultural Advisory Service.
For species with LD50 close to or above <strong>the</strong> corresponding field dose,
repeated spraying will also increase <strong>the</strong> probability of <strong>the</strong> individual
being hit and affected by an application. The advantage or disadvantage
of split dosing (i.e. <strong>the</strong> full dose is distributed over several applications
with reduced dose) for harmless organisms thus seems to depend on <strong>the</strong>
species’ sensitivity to <strong>the</strong> dosage used. It is <strong>the</strong>refore interesting to
compare <strong>the</strong>se considerations with observations in <strong>the</strong> field. Split dosing
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