Exposure of Bombus terrestris L. to three different active ingredients and two application methods for olive pest control

A potential cause of bumblebee losses on farmland is probably the toxic effects of insecticides used against crop pests. The olive fruit fly, Bactrocera oleae, is a major pest of olive trees in Mediterranean countries, so spray treatments (cover and bait sprays) are applied for this and other minor pests starting in early spring. The objective of this study was to determine the effect of three pesticide spraying solutions (alpha-cypennethrin, dimethoate, and spinosad) and control methods used against olive fruit flies and other olive tree pests, on adult buff-tailed bumblebees, Bombus terrestris (Hymenoptera: Apidae). The results indicated that exposing worker bumblebees to enviromnentally realistic levels of these active ingredients in the laboratory resulted in high mortality rates of 34% (alpha-cypermethrin, cover spray) and 54% (alpha-cypermethrin, bait spray) at the end of the three-day exposure period. Bumblebees are probably at a high risk of mortality when they forage in olive groves with dry residues of a bait solution of a-cypennethrin (which resulted in 54% mortality in this study). Spinosad and dimethoate posed a lower risk of mortality for bumblebees. However, when the tested chemicals were applied to the whole tree canopy and without the bait attractant, the recorded mortality for dimethoate and a-cypennethrin was 8% and 34%, respectively. This study contributes to optimizing the use of the tested active ingredients as well as the applied control methods against managed pests, because it inflicts definite damage to populations of bumble bees and other non-target pollination.