Assessment of the distribution of an insecticide applied to wheat tillers under field conditions.

In order to carry out a relevant assessment of pesticide toxicity towards beneficial arthropods under field conditions, it is important to have an accurate and reliable knowledge of the distribution of pesticide residues over the entire plant. As the compound is not homogeneously distributed over the plant, insects can encounter very different residue concentrations. The work presented aims to determine the quantities of deltamethrin residue on seven specific parts of the wheat tillers after spraying in the field. The results obtained indicate that the total quantity of pesticide applied per unit area represents only 40% of the maximum theoretical amount that would be expected on a horizontal surface area. Logically enough, a third of the spray deposit can be found on the flag leaf and over 70% is found on the entity formed by the ear and the two last leaves. On the other hand, the amounts recovered on the stalk are limited and do not exceed 10% of the total residue. Thus, beneficial arthropods are not exposed to pesticide amounts per unit area as high as those envisaged during standard toxicity tests carried out under laboratory conditions.