Determination of residues of some insecticides in clover flowers: A bioassay method using honeybee adults
S. A. Mansour* and M. K. Al-Jalili
Residues of 6 insecticides sprayed on clover (Trifolium alexandrinum) were determined biologically using adult honeybees (Apis mellifera L.) as test insects. Flower samples were extracted with acetone and extracts were applied topically to bees without need to remove co-extractives (i.e., without clean-up). Mortalities were recorded 24 h after application and the results were used to establish dosage-mortality relationships for each insecticide. The LD50 values (μg/bee) were 0.066, 0.068, 0.112, O.115, 0.212 and 0.310 for pirimiphos-methyl, methomyl, propoxur, chlorpyrifos, carbaryl and fenitrothion respectively. Recoveries of the tested insecticides from flower samples that had had known amounts of insecticides added to them ranged from 80% to 110%. Residues (expressed as ppm) in clover flowers 2, 4, 7 and 10 days after application are presented; methomyl was the most persistent compound, chlorpyrifos the least.