Oral exposure to thiacloprid-based pesticide (Calypso SC480) causes physical poisoning symptoms and impairs the cognitive abilities of bumble bees

Abstract

Background: Pesticides are identified as one of the major reasons for the global pollinator decline. However, the sublethal effects of pesticide residue levels found in pollen and nectar on pollinators have been studied little. The aim of our research was to study whether oral exposure to the thiacloprid levels found in pollen and nectar affect the learning and long-term memory of bumble bees. We tested the effects of two exposure levels of thiacloprid-based pesticide (Calypso SC480) on buff-tailed bumble bee (Bombus terrestris) in laboratory utilizing a learning performance and memory tasks designed to be difficult enough to reveal large variations across the individuals.

Results: The lower exposure level of the thiacloprid-based pesticide impaired the bees' learning performance but not long-term memory compared to the untreated controls. The higher exposure level caused severe acute symptoms, due to which we were not able to test the learning and memory.

Conclusions: Our results show that oral exposure to a thiacloprid-based pesticide, calculated based on residue levels found in pollen and nectar, not only causes sublethal effects but also acute lethal effects on bumble bees. Our study underlines an urgent demand for better understanding of pesticide residues in the environment, and of the effects of those residue levels on pollinators. These findings fill the gap in the existing knowledge and help the scientific community and policymakers to enhance the sustainable use of pesticides.

Keywords: Associative learning; Bombus terrestris; Bumble bee; Insecticide exposure; Neonicotinoids; Pollinator; Sublethal effects.

Fig. 1

The figure illustrates the symptoms observed in ten minutes intervals for 1 h after the thiacloprid exposure of the studied bumble bees in treatment 2

Fig. 2

The left side of the figure shows the predicted levels of performance (proportion of correct decisions) and its 95% confidence band for the sample values of performance in the learning phase. Circles on the right side of the figure represent model estimates of performance and error bars represent confidence levels at 95% for the sample values of performance in the memory test. Black bars above each learning bout represents the number of sample values per bout. The horizontal dashed line indicates the chance level (50%)

Fig. 3

Flight arena with the colour chips. The colour patches under the titles ‘sugar’ and ‘quinine’ indicate whether the chips of the respective colours had 7 µl 40% sucrose solution or saturated quinine solution