Honeybees

Navigation in honeybees is studied with the help of a special radar that allows to trace the flights of individual bees over kilometers. In a typical experiment, the bees were trained to a feeder or they follow a dancing bee. Then we equipped one bee with a radar transponder and released it at a site within the range of the explored area. First, the animal performs a straight flight that would have brought it back from the feeder to the hive (vector flight) would it not have been transported to a different site. In the case of the dance follower, the bee performs the vector information transmitted in the dance, as described by Karl von Frisch and followers. Then the bee loops around (search flight), followed by a straight return flight to the hive (homing flight). We carried out the experiments in an area where the skyline of the horizon or a beacon at the hive did not guide the bees’ navigation. Thus, the bees referred only to the pattern of landmarks on the ground. We show that the memory structure used by the bees can be best conceptualized as a cognitive map storing the geometric relations of landmarks and important locations. Sublethal doses of neonicotinoids interfere selectively with the homing flight component based on this cognitive map memory, reducing the probability of successful returns to the hive. Chronic exposure to the neonicotinoid Thiacloprid reduces the attractiveness of a feeding site and the rate of recruitment.

Wir verwenden ein spezielles Radargerät, um den Flug von einzelnen Bienen über Kilometer zu verfolgen. Das Design der Versuche zum Studium ihrer Navigationsleistungen besteht darin, Bienen nach einer Dressur auf einer Futterstelle oder nach dem Verfolgen einer Tänzerin am Stockausgang mit einem Transponder auszustatten und an einer anderen Stelle innerhalb ihres explorierten Areals freizulassen. Sie führen dann zuerst einen Vektorflug durch, der sie entweder zum Stock zurück gebracht hätte (wären sie nicht versetzt worden) oder zu der im Tanz angegebenen Futterstelle. Danach führen sie einen Suchflug durch, von dem sie auf direktem Flug zum Stock zurückkehren. Die Experimente sind so angelegt, dass die Bienen sich dabei nicht nach einem Horizontprofil oder einer Landmarke in der Nähe des Stockes, sondern ausschließlich nach der Bodenstruktur orientieren können. Wir weisen nach, dass das Navigationsgedächtnis der Bienen am besten als eine kognitive Karte beschrieben werden kann. Subletale Dosen von Neonicotinoiden stören selektiv die Heimflugphase, die auf der Verwendung dieses kartenartigen Gedächtnisses beruht, sodass die Tiere dann nicht mehr sicher zum Stock zurückfinden. Eine chronische Aufnahme von Thiacloprid reduziert die Sammelaktivität und die Tanzkommunikation.

In recent years, populations of honey bees and other pollinators have been reported to be in decline worldwide. A number of stressors have been identified as potential contributing factors, including the extensive prophylactic use of neonicotinoid insecticides, which are highly toxic to bees, in agriculture. While multiple routes of exposure to these systemic insecticides have been documented for honey bees, contamination from puddle water has not been investigated. In this study, we used a multi-residue method based on LC-MS/MS to analyze samples of puddle water taken in the field during the planting of treated corn and one month later. If honey bees were to collect and drink water from these puddles, our results showed that they would be exposed to various agricultural pesticides. All water samples collected from corn fields were contaminated with at least one neonicotinoid compound, although most contained more than one systemic insecticide. Concentrations of neonicotinoids were higher in early spring, indicating that emission and drifting of contaminated dust during sowing raises contamination levels of puddles. Although the overall average acute risk of drinking water from puddles was relatively low, concentrations of neonicotinoids ranged from 0.01 to 63 µg/L and were sufficient to potentially elicit a wide array of sublethal effects in individuals and colony alike. Our results also suggest that risk assessment of honey bee water resources underestimates the foragers' exposure and consequently miscalculates the risk. In fact, our data shows that honey bees and native pollinators are facing unprecedented cumulative exposure to these insecticides from combined residues in pollen, nectar and water. These findings not only document the impact of this route of exposure for honey bees, they also have implications for the cultivation of a wide variety of crops for which the extensive use of neonicotinoids is currently promoted.

In a letter submitted for today’s White House “listening sessions” deadline, over 100 scientists from diverse disciplines (including Dutch toxicologist Henk Tennekes) cited the growing body of evidence that neonicotinoids and other systemic pesticides harm bees. These scientists called on leaders of President Barack Obama’s Pollinator Health Task Force to take action on pesticides to protect and promote healthy populations of bees and other pollinators.