Aphid attack, predators, infections by beet yellowing viruses and yields in fields of sugar beets with different insecticidal soil and seed treatments

In laboratory tests, larvae of Poecilus cupreus L. (Col., Carabidae) in soi l proved to be less susceptible to imidacloprid than to carbofuran, when ap plied to seed Fills of sugar beets. In field experiments (1991-93, aphid at tack was always highest in plots with lindane (200 g a. i./ha, only). Numbe rs of predatory arthropods on beet leaves and on the soil surface were low in plots with lindane (spray at seeding) and with imidacloprid tin pills), and high in plots with carbofuran and without My insecticide. Aphids per pr edator were equal in all treatments except lindane, where aphid numbers wer e twofold. Correlations were nor significant, but a tendency was observed, that the incidence of yellowing viruses was dependent on the;Myzus persicae /predator-relationship: The more predators, the lower the incidance of yell owing viruses. In case of high incidence of yellowing viruses tin 1993), su gar beet yields were higher in imidacloprid- and lindane- than in carbofura n-plots. This indicates that in 1993 aphid attack and late virus infections had no effect on yield. With initial double seed, carbofuran treatment (pi lls) yielded more than "no insecticide". Sugar content was highest in imida cloprid-plots. The mechanisms leading to the results observed are discussed .