Is honeybee colonies mortality related to insecticide use in agriculture?

Imidacloprid is systemic insecticide belonging to the group of neonicotinoids, which is often used in agriculture and household. Oral LD50 for honeybee is 37-206 ppb (3.7-20.6 ng/bee). Olfactory response of honeybee is trigged at 10 ppb of the insecticide in the food. 20 ppb and higher concentration disturbs significantly central nervous system of the honeybee. Sunflowers, which seeds were treated with Gaucho (contains imidacloprid), had concentration of imidacloprid below 10 ppb (0.01 mg/kg). It has been reported 1.9 ppb in nectar and 3.9 ppb in pollen of the sunflower. However, foraging honeybees contained 5 and 8 ppb of imidacloprid and its metabolites. When imidacloprid was applied to the thorax of the honeybee, it had been shown that at liest 5 ng/bee is needed to increase threshold of sugar concentration, which released proboscis extension. Imidacloprid is metabolized in honeybee body in 4.5 to 5 hours. The highest concentration of the dangerous products 5-hydroxiimidacloprid and olefin was detected 4 hours after feeding. Based on fast degradation of imidacloprid it exist reasonable doubt that honeybees which took higher amounts of imidacloprid died already outside of the hive and before final death of the colony as well before samples were taken. In our recent incident, selected sampling methodology was shown to be problematic. That could had an undefined effect on analysis results. Based on beekeepers report 13 apiaries were under veterinary examination. Samples of bees and in 7 cases also samples of comb pollen were taken for further analysis. All sampled colonies were affected by Varroa destructor (varoa) and most of them also with Nosema apis. Colonies were also affected by long lasting dry period and not adequate natural food supply previous summer. Chemical analysis showed presence of imidacloprid and its metabolites in 12 samples of bees. 5 of them had detected concentration higher then 5 ppb. On the other hand the insecticide was not detected in pollen samples. Possible effect of sub lethal intoxication with the insecticide on the increase of parasites and diseases could not be excluded. In the samples of bees with higher concentration then 5 ppb of imidacloprid and metabolites intoxication with the insecticide could be major reason for the death of the colonies. Based on known degradation processes, bees had to have at list 10 ppb of imidacloprid and metabolites in their bodies at the time of possible intoxication. Such high concentration could be enough to cause sublethal effects on single bee, and had an effect on colony decline. In a current paper we discuss possible future research of imidacloprid effects on single bee as well to whole colony.