Acute toxicity of cypermethrin and fenitrothion on honeybees (Apis mellifera mellifera) according to age, formulations and (chronic paralysis virus)/insecticide interaction.

The LD50 parameter used to evaluate the acute toxicity of chemical compounds on animals-especially honeybees-can vary in accordance with many factors. The LD50 of two classes of insecticides, cypermethrin (a pyrethroid) and fenitrothion (a organophosphate) were calculated on worker honeybees (Apis mellifera mellifera) under various conditions: insecticide's formulations, age of bees, and CPV (chronic paralysis virus)/insecticide interaction. LD50 for pure standards of cypermethrin (0.16 +/- 0.21 mu g/bee) and fenitrothion (0.27 +/- 0,031 mu g/bee) were significantly different (P<0.05) from those of commercial formulation as cymbush (0.26 +/- 0.07 mu g/bee) [100g of cypermethrin per litre of petroleum ether], and folithion (0.38 +/- 0.2 mu g/bee) [550g of fenitrothion per litre of petroleum ether]. The LD50 calculated on newly emerged bees (age< 1 day) for cypermethrin (0.16 +/- 0.03 mu g/bee) and fenitrothion (9.27 +/- 0.08 mu g/bee) varied significantly (P<0.05) from those calculated on adult bees, i.e.: cypermethrin 0.21 +/- o.01 mu g/bee, and fenitrothion 0.42 +/- 0.10 mu g/bee. We also demonstrated that CPV increases the acute toxicity of cypermethrin on newly emerged bees. In fact LD50 of cypermethrin (0.16 +/- 0.03 mu g/bee) decreased in presence of CPV (0.06 +/- 0.01 mu g/bee), hence acute toxicity was increased by factor k=2.66. In another experiment honeybees received separately or jointly during 7 days cypermethrin at 10 mu g/liter of sucrose syrup and 1 mu l of viral solution diluted at 10(-6). In case of interaction tratement, we noticed that the correlated increase of death rate and decrease of sucrose consumption of caged bees, behaved differently with significance (P<0.05) from those which received separately cypermethrin or CPV.