Effects of sublethal doses of deltamethrin (Decis Ce) on Bombus terrestris
J -N Tasei; H Sabik ; L Pirastru ; E Langiu; J M Blanche; J Fournier; J P Taglloni
Experimental 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 lifespan was observed in either case of contamination in laboratory conditions. Queens were fed with a sugar solution contaminated by 0.01-0.2 mg/I of deltamethrin during either a 5-day period or continuously. None of these treatments affected the size of the first batch of workers produced by the queen or the period from egg to emergence. It is suggested that some deltamethrin detoxification might be due to intestinal enzymes. The effectiveness of this detoxification would be enough to prevent the bees from oral intoxication after collecting nectar from rape flowers sprayed with deltamethrin at rates much greater than the registered one.