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Abstract
The aim of this work was to propose methods to test mechanisms of synergistic effects of toxic agents in bees. We assumed that the fungicide prochloraz acts synergistically on deltamethrin by increasing the penetration of deltamethrin and/or inhibiting the oxidative metabolism of deltamethrin. These hypotheses were tested by using a pharmacokinetic box model. A previous experimental work showed that there was a synergy between deltamethrin and prochloraz in bees, and allowed to compare the effects of the treatment with 0.25 g ha−1 deltamethrin in the presence of 25 g ha−1 (Δ0.25 + P) prochloraz and the treatment with 1 g ha−1 deltamethrin alone (Δ1). We postulated that cumulated mortality was proportional to the cumulated internal deltamethrin (ID 2). To be consistent with the experimental data, ID 2 of treatment (Δ0.25 + P) had to be greater than ID 2 of treatment (Δ1) during the period from 2 to 8 hours. We studied in the most favourable conditions if the different hypotheses could be consistent with the experimental data. The conclusions were that published parameter values would be consistent with simulation results only in the case of an action on both metabolism and possible active transports during penetration, whereas inhibition of metabolism and increase in penetration, by increasing diffusion, would not be sufficient to explain the synergy.