Changes in the frequency of feeder visits after treatment with imidacloprid or clothianidin.

<p>During 3-hour observation periods, we recorded the frequency of visits at the feeder immediately after treatment (a.t.) and up to 48 h after treatment (24 h a.t., 48 h a.t.). Values inside the bars: n = Number of bees returning to the feeder after treatment, % = (bees returned/bees treated)*100, (<b>A</b>) Oral administration with 0.15 ng imidacloprid did not affect the visit frequency per bee significantly, while 1.5 and 3 ng imidacloprid led to a significant reduction of feeder visits compared to the controls during the first three hours immediately after treatment. Not all bees treated with 3 ng reappeared at the feeder immediately after treatment, but almost all returned regularly after 24 h. No bees treated with 6 ng imdacloprid returned in the first three hours of observation after treatment. After 24 h only three of twelve bees returned to forage from the feeder. (<b>B</b>) The frequency of visits was not affected negatively after administration of 0.05 ng clothianidin, while treatment with 0.5 ng, 1 ng, and 2 ng clothianidin reduced the frequency of visits significantly compared to the control group during the first three hours immediately after treatment. As shown here, only 67.8% and 11.8% of the bees treated with 1 ng and 2 ng, respectively returned to forage at the feeder. The missing bees were not registered again during the experiments. The significant reductions to the visit frequency by both substances did not persist on the following day. * = p<0.05, ** = p≤0.01, *** = p≤0.001.