Effects of sublethal doses of deltamethrin (Decis Ce) on Bombus terrestris

SUMMARYExperimental plants of oilseed rape (Brassica napus cv. oleifera) were sprayed with deltamethrin at a rate of 12.5 g/ha, which is regarded as producing sublethal effects for Bombus terrestris workers foraging on the flowers. Contamination levels were assessed before and after treatment in small samples: 1.0 g of anthers, 0.7–2.0 g of nectar, 0.4–3.5 g of honey, 1.0 g of workers. Weights of residues ranged from 0.002 to 0.006 mg/kg in honey, from 0.012 to 0.019 mg/kg in nectar, from 0.047 to 0.605 mg/kg in anthers and from 0.149 to 0.932 mg/kg in workers. Six days after spraying no residues could be detected in anthers and nectar (detection thresholds = 0.0012–0.0062 mg/kg). In laboratory tests, contamination of worker bees by a topical application of 0.08–0.16 mg/kg of deltamethrin resulted in an increased uptake of sugar solution from a feeder by 40–100%. Contamination of the sugar solution by 0.1–0.2 mg/kg of deltamethrin resulted in a reduction of food uptake by 47–59%. No negative effect on lif...