The influence of pesticides repellency used in oilseed rape (Brassica napus subsp. napus) on the preference by bees (Apis mellifera L.)

Abstract

The occurrence of honey bees was observed in fields of oilseed rape (Brassica napus subsp. napus) during the flowering period. The investigation revealed that the farmer was using different pesticides against pests and diseases during that time. Experiments using the feeding stations (Free-Choice Trials) method with honey solutions containing pesticides revealed that the repellency effect of pesticide formulations is different with some even attractive to honey bees. Experiments were held outdoors close to bee colonies and indoors in a fly-through hall in controlled conditions and commercial pesticides were used. The highest repellency in outdoors/indoors experiments was observed using the solution with formulations of pesticide Horizon 250 EW (a. c. tebuconazole) – 96.5%/99% and Nurelle D (a. c. chlorpyriphos-cypermethrin) 88%/97%, and the lowest repellency was observed for solution with formulations of Plenum (a. c. pymetrozine) – 19.2%/27.8%, Mospilan 20 SP (a. c. acetamiprid) – 20%/23.8%. The most repellent pesticides were diluted to half and a quarter of the recommended dose. The reducing of the active ingredient concentration improved attractiveness to honey bees, especially with Trebon OSR (74.3% for half dose and 55.8 for quarter dose) and Nurelle D (77.8% for half dose and 66.7 for quarter dose). However, a quarter dose of Horizon 250 EW did not show any substantial change in repellency (90.7%). Further investigations in field conditions will be done.