Characteristics of Imidacloprid Toxicity in Two Apis Mellifera Subspecies

Abstract

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.

Modes of honeybees exposure to systemic insecticides: estimated amounts of contaminated pollen and nectar consumed by different categories of bees

“…In particular, it might modify the learning and orientation abilities of honeybees at concentrations as low as 0.1 ng/bee ) and 1.25 ng/bee (Lambin et al, 2001). However, these results might vary according to honeybees age , race (Suchail et al, 2000), colony , and season .…”

Scientific Opinion on the science behind the development of a risk assessment of Plant Protection Products on bees (Apis mellifera,Bombusspp. and solitary bees)

“…However, even though the methodology is supposed to be standardised and results are thought to be reproducible, active substances have shown different acute mortality values among studies. The oral LD50 of Imidacloprid, for example, is observed between 3.7 and 40.9 ng/bee (48h; Schmuck et al, 2001), 5 ng/bee (48h; Suchail et al, 2000) or 40 and 60 ng/bee (48h and 72 h, respectively, Suchail et al, 2001), 49 and 102 ng/bee (48h;Nauen et al, 2001), and 490 ng/bee (48h; DEFRA, 2007). Fipronil showed oral LD50 from 4-6 ng/bee (48h, Aliouane et al, 2008) to 123 ng/bee (48h; DEFRA, 2007).…”

Standard methods for toxicology research inApis mellifera

“…From an experimental point of view, the graph of the cumulative distribution function is not necessarily sigmoidal. For instance, after one imidacloprid contact exposure, Medrzycki et al Suchail et al (2000) evidenced that mortality rates were positively correlated with doses lower than 7 ng/bee and negatively with doses ranging from 7 to 15 ng/bee. In this situation, the calculation of any lethal dose with the log-probit model is incorrect.…”

“…At the individual level, subspecies and strains of honey bees are not equally susceptible to a given dose of AI (Ladas, 1972;Suchail et al, 2000). Moreover a colony is not genetically homogeneous because of the coexistence of half-sister workers.…”