Guttation and risk for honey bee colonies (Apis mellifera L.): Use of guttation drops by honey bees after migration of colonies - a field study

Background: The aim of this experiment was to investigate whether honeybees from colonies that are not familiar with their surrounding landscape, due to short-distance migration to a new location, are more at risk by guttation drops from seed-treated plants than bee colonies which are already familiar with alternative water sources in the surrounding of their apiary. Results: The mean mortality of bees, which occurred after moving beehives to a new location, increased only slightly from 6 bees/day (-1 day before moving) up to a maximum of 21 bees/day (1 day after moving). No significant differences in the mean number of dead bees between bee colonies that were familiar with all sites of water sources in the surrounding area and bee colonies that were only recently moved to the field were observed. Conclusion: There was no indication that honey bee colonies which were not familiar with the surrounding landscape are more at risk by guttation drops from seed-treated plants than bee colonies which are already familiar with the alternative water sources in their surrounding landscape. Keywords: guttation, seed treatments, transport beehives, pesticides, honey bee, water forager

Guttation and the risk for honey bee colonies (Apis mellifera L.): a worst case semi-field scenario in maize with special consideration of impact on bee brood and brood development

Background: The possible risk of guttation for bees was investigated in two semi-field studies with maize treated with clothianidin. In a worst-case scenario set-up the effects on adult and brood mortality of bees with special consideration of the brood development of the bees were assessed. Results: Due to the weather conditions in the first experiment guttation occurred only once, which caused a high mortality and a brood-termination rate of up to 100 % in the worst-case scenario without additional water supply but no clear increase of mortality or brood termination was observed when water was supplied. In the second experiment guttation in maize occurred on 5 of 10 days. The mortality in treated variants with water supply and control variants with untreated seeds was on a similar level and within normal range. The brood-termination rate was in the control below 16 %, in the treatment from 16 to 43 %. Conclusion: In the first experiment in the variant with treated maize and no additional water supply, an artificial and extreme situation a high impact on mortality and also on the brood development was observed, indicating the sensitivity of the test system but representing an unrealistic worst case scenario. In variants with treated maize and additional water supply no clear effects on adult mortality and brood were observed in the first and the second experiment. Keywords: honey bees, guttation, pesticides, clothianidin, seed treatments, brood developmen

Water collection by honey bees – How far will foragers fly to use water sources like guttation drops? A first distance trial using cereals and oilseed rape

Background: Depending on the location, various water sources may be available for bee colonies. These sources can be permanent, such as ponds, or incidental like dew or guttation droplets. The aim of the experiment was to investigate whether bees prefer guttation drops as a water source compared to dew or rain drops. Furthermore it was analysed if bees use these water sources up to a distance of 50m from their hives. Results: During the experiment 147 bees were observed scanning the surface of the plants without landing, 13 bees took up guttation fluid and 36 bees collected dew or rain drops. Few bees were observed collecting guttation fluid at 50m from their hives but most in close proximity of the hives. Furthermore, in some dead bees residues of the seed treatment were detected (imazalil: 0.0011 μg/bee – 0.329 μg/bee; LD50= 35.1 μg/bee). Conclusion: In the majority of observations, bees were spotted scanning the leaf area of the plants. Only single bees were observed that actually took up water from plant leaves. It seems these bees did not distinguish between dew, rain or guttation droplets. The majority of water collecting or bees resting on plants were observed in the close proximity of their hives. Keywords: guttation fluid, pesticides, seed treatment, honeybee, water source, distanc

Frequency and intensity of guttation events in different crops in Germany

Background: In crops of economic relevance and some common weeds in Germany, several glasshouse and field trials were conducted at the JKI and cooperating research partners (DWD, IfZ, BDP and UFOP) from 2009 to 2011. Aim of the investigations was to analyze the guttation frequency of these crops, to document climatic conditions that trigger guttation and to describe the quality and quantity of guttation events (e.g. size/number of drops). Results: Guttation occurred in all crops mainly at young growth stages. Only maize, cucumber, oilseed rape and potato produced guttation droplets until emergence of inflorescence. The excreted amount of fluid was comparable for maize and oilseed rape but considerably lower for sugar beet and barley. In field situation guttation occurred frequently in more than one plant species in parallel when it was not dry or too windy or frosty. Conclusion: Monocotyledonous crops and weeds showed a higher guttation frequency than most dicotyledonous crops. Maize showed large guttation drops even under low relative air humidity, whereas guttation drops in sugar beets were much smaller and only observed under very high humidity conditions (>90%). Other dicotyledonous crops, such as oilseed rape and potato, showed a much higher guttation frequency than sugar beets. Keywords: guttation, honey bees, pesticides, crops, weed