EFFECTS OF SUBLETHAL DOSES OF DELTAMETHRIN (DECIS-CE) ON BOMBUS-TERRESTRIS

Experimental plants of oilseed rape (Brassica napus cv. oleifera) were sprayed with deltamethrin at a rate of 12.5 g/ha, which is regarded a s producing sublethal effects for Bombus terrestris workers foraging o n the flowers. Contamination levels were assessed before and after tre atment 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 0.0 47 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 tes ts, contamination of worker bees by a topical application of 0.08-0.16 mg/kg of deltamethrin resulted in an increased uptake of sugar soluti on 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 lifespan was observed in either case of contamination in laboratory conditions. Queens were fed with a sugar s olution contaminated by 0.01-0.2 mg/l of deltamethrin during either a 5-day period or continuously. None of these treatments affected the si ze of the first batch of workers produced by the queen or the period f rom egg to emergence. It is suggested that some deltamethrin detoxific ation might be due to intestinal enzymes. The effectiveness of this de toxification would be enough to prevent the bees from oral intoxicatio n after collecting nectar from rape flowers sprayed with deltamethrin at rates much greater than the registered one.