Sub-lethal pesticide exposure interferes with honey bee memory of learnt colours.

Neonicotinoid pesticide use has increased around the world despite accumulating evidence of their potential detrimental sub-lethal effects on the behaviour and physiology of bees, and its contribution to the global decline in bee health. Whilst flower colour is considered as one of the most important signals for foraging honey bees (Apis mellifera), the effects of pesticides on colour vision and memory retention in a natural setting remain unknown. We trained free flying honey bee foragers by presenting artificial yellow flower feeder, to an unscented artificial flower patch with 6 different flower colours to investigate if sub-lethal levels of imidacloprid would disrupt the acquired association made between the yellow flower colour from the feeder and food reward. We found that for doses higher than 4 % of LD value, the foraging honey bees no longer preferentially visited the yellow flowers within the flower patch and instead, we suspect, reverted back to baseline foraging preferences, with a complete loss of the yellow preference. Our honey bee colour vision modelling indicates that discriminating the yellow colour from the rest should have been easy cognitive task. Pesticide exposure also resulted in a significant increase in Lop1, UVop, and Blop, and a decrease in CaMKII and CREB gene expression. Our results suggest that memory loss is the most plausible mechanism to explain the alteration of bee foraging colour preference. Across bees, colour vision is highly conserved and is essential for efficient pollination services. Therefore, our findings have important implications for ecosystem health and agricultural services world-wide.