ACUTE ORAL TOXICITY OF NEONICOTINOIDS ON DIFFERENT HONEY BEE STRAINS

Neonicotinoids are a class of relatively new insecticides, designed in the '80s, characterized by their excellent feedback, since they are highly systemic and with long-term persistence. These insecticides, however, show very strong toxicity to pollinating insects and in particular to the honey bee, besides causing also other effects which are often not easily identifiable, such as behavioural disturbances, orientation difficulties, and impairment of social activities. During the past few years, in many countries, alarming bee mortality rates were recorded. In some cases this was clearly due to the use of neonicotinoids either for seed dressing or crop spraying. It was therefore considered appropriate to test on three strains of Apis mellifera of Piedmontese origin and referable to A. m. ligustica in the laboratory both the acute oral toxicity of Imidacloprid, which had been, in use for many years, and Clothianidin and Thiametoxam, only more recently introduced in Italy. To reach this aim, methods developed at the Di.Va.P.RA. and applied in several previous studies, were used. Commercial products were used throughout the tests. They were tested at the recommended concentration for field treatments. When mortality was higher in the tested bees than in the untreated ones, the active ingredients were tested at gradually decreasing concentrations so as to reach a mortality not significantly different from that found in the untreated controls. The LD50 calculated for Clothianidin and Thiametoxam were lower than for Imidacloprid; the differences between the honey bee strains for the same active ingredient were slight.