I could not find the whole paper unless you pay a subscription. 

Abnormal Foraging Behavior Induced by Sublethal Dosage of Imidacloprid in the Honey Bee 
(Hymenoptera: Apidae)

Authors: Yang, E. C.; Chuang, Y. C.; Chen, Y. L.; Chang, L. H.

Source: Journal of Economic Entomology, Volume 101, Number 6, December 2008 , pp. 1743-
1748(6)

Abstract 
Although sublethal dosages of insecticide to nontarget insects have never been an important 
issue, they are attracting more and more attention lately. It has been demonstrated that low 
dosages of the neonicotinoid insecticide imidacloprid may affect honey bee, Apis mellifera L., 
behavior. In this article, the foraging behavior of the honey bee workers was investigated to show 
the effects of imidacloprid. By measuring the time interval between two visits at the same feeding 
site, we found that the normal foraging interval of honey bee workers was within 300 s. However, 
these honey bee workers delayed their return visit for >300 s when they were treated orally with 
sugar water containing imidacloprid. This time delay in their return visit is concentration-
dependent, and the lowest effective concentration was found to be 50 μg/liter. When bees were 
treated with an imidacloprid concentration higher than 1,200 μg/liter, they showed abnormalities 
in revisiting the feeding site. Some of them went missing, and some were present again at the 
feeding site the next day. Returning bees also showed delay in their return trips. Our results 
demonstrated that sublethal dosages of imidacloprid were able to affect foraging behavior of 
honey bees.

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