The impact of landscape complexity and composition on honey bee visual learning

Abstract

Over the past few decades there has been an overall decline in the number of pollinators, including wild bees, partly due to stress factors such as the availability of food resources, nest site availability and pesticide usage. Managed honey bees have also been negatively impacted in certain regions, such as the USA. One of the major stress factors facing bees currently is land use change, where natural landscapes are decreasing and often converted to either agricultural or urban land. Here, we assess directly the link between landscape diversity, edge density and honey bee learning, by analysing how honey bee visual learning ability varies across different landscapes, using a field-adapted version of the proboscis extension response. It was previously thought that honey bees from hives based in different landscapes may vary in visual learning abilities because of their different experiences and neural plasticity. Thus, bees that have experience in more complex learning environments may do better in learning tasks. To test this, bees were taught to associate a coloured yellow paper strip with a positive sugar reward and a blue coloured strip with a negative salt reward. Results showed that as edge density increased in the landscape, visual learning in bees reduced, and when landscape diversity increased, so did learning. This is important as bees must learn foraging routes, find profitable flowers and develop spatial maps, as well as recognise intruders. If their cognitive abilities are reduced and they are unable to carry out these tasks, this will be detrimental for the continuous development of the colony.

Keywords: Apis; Apidae; Honey bee; Landscape; Learning.

Fig. 1.

Twenty-six apiaries located across southern England identified for this study. The 12 apiaries used in this study are indicated by a blue circle, which represents the 1 km buffer zone around each hive. Closeups are displays of these sites. Yellow circles represent apiaries that were not chosen. Habitat types were obtained at a 25 m resolution from images collected by the Landsat 5 Thematic Mapper, from EDINA Digimap.

Fig. 2.

Spearman correlation coefficients between total edge length and Shannon's landscape diversity (H) at the chosen 12 apiary sites. Little correlation was found between landscape diversity and total edge length (s=9,774,066, ρ=0.052, P=0.130).

Fig. 3.

Honey bees show a conditioned response across five consecutive learning trials. Learning improved across trails and the greatest number of bees successfully choosing the sugar reward was at trial 5. From trial 2 onwards, significantly more bees chose the positive reward than the negative. Black bars represent the bees that did not learn the conditioned response, and thus chose the blue negative strip containing salt water. Clear bars represent bees that learned the conditioned response, and thus chose the yellow strips containing the sugar water (n=934).

Fig. 4.

The effect of landscape diversity and total habitat edge on the percentage of bees choosing the sugar reward (n=934). (A) There was a positive effect of landscape diversity (Shannon's H) on the percentage of bees that correctly chose the sugar reward. Bees in landscapes with low total edge made more correct choices compared with bees in landscapes with high total edge.