Characteristics of imidacloprid toxicity in two Apis mellifera subspecies

Imidacloprid (1‐(6‐chloro‐3‐pyridylmethyl)‐N‐nitroimidazolidin‐2‐ylideneamine) belongs to a new chemical family of chloronicotinyl compounds whose mode of action on the insect nervous system differs from that of traditional neurotoxic products. Imidacloprid, a strong systemic compound, is effective against several sucking and mining pests. The acute toxicity of contact and oral applications on two Apis mellifera subspecies, Apis mellifera mellifera and Apis mellifera caucasica, was investigated. In all toxicological studies, each dose included three cages of 20 individuals and each study was replicated three times. The dose‐mortality relation revealed some unusual characteristics. At low imidacloprid concentrations, a biphasic mortality appeared, particularly with the contact exposure route. At moderate doses, mortality profiles at 24 and 48 h were different only after oral application. Response kinetics showed that mortality was delayed at the higher doses of imidacloprid. After oral intoxication, the LD50 values of imidacloprid at 24 and 48 h were about 5 ng/bee for both A. m. mellifera and A. m. caucasica. After contact application, the LD50 values at 24 and 48 h were approximately 24 ng/bee for A. m. mellifera and 14 ng/bee for A. m. caucasica. Imidacloprid ranks among the more potent contact insecticides in this important pollinator species.