“Our findings are of general importance in light of the controversial and vehement discussions currently underway regarding the use of pesticides known as neonicotinoids, which adversely affect the nervous system of insects to the extent of killing them,” says Randolf Menzel. Pesticides are intended to protect plants from pests. Within a group of pests, however, pesticides often function in various ways, and scientists have found that a distinction between harmful and beneficial insects is not usually possible, as the underlying mechanisms in all the insects are very similar. “For all these reasons, particular care and responsibility must govern the use of pesticides,” stresses Randolf Menzel. The European Commission has banned the use of two pesticides for the next two years to give scientists an opportunity to study their effects on pollinating insects in more detail.
Bees use the position of the sun for orientation in memorizing their flights around the hive. They develop an “internal map” for storing their flight routes. With the aid of a flight vector they know the direction and distance to the hive. In an experiment scientists at Freie Universität Berlin tested the effects of the two currently banned pesticides imidacloprid and clothianidin as well as a pesticide still being used, thiacloprid, on the ability of the bees to find their way.
The researchers at Freie Universität proceeded as follows: First, they trained a group of bees at a feeding station about 400 m from the hive. The bees learned to fly a direct route to the feeding site. In a second step the scientists caught the conditioned bees before they left the hive and released them in a different location within their explored area. Upon release the bees first used their memory of the flight vector, flying in the direction and over the distance of where they expected the hive to be, based on their original location. Since their starting point had changed, the hive was not where they expected it to be. After some searching around, the bees’ “internal map” enabled them to re-orient themselves, and they returned to the hive.
In the test situation, the navigation of the bee has two phases, the so-called vector flight and the so-called homing flight. In a third step, the test bees were administered a small amount of the pesticide in their feed. It turned out that their sense of direction during the homing phase was disturbed by the insecticide. Significantly fewer bees successfully returned to the hive, and overall, the flight paths were less direct. It should be noted that these results were obtained by testing individual bees, and it is still not clear how the pesticides affect an entire colony of bees.
In their publication “Neonicotinoids interfere with specific components of navigation in honeybees,” the scientists discuss the results of their study in the context of the application of pesticides.
Johannes Fischer, Uwe Greggers, Bernd Grünewald, Randolf Menzel. 2014. Neonicotinoids interfere with specific components of navigation in honeybees. URL: www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0091364.