Brains and brain components in African and European honey bees (Hymenoptera: Apidae) - a volumetric comparison

Authors: DeGrandi-Hoffman, Gloria; LUCAS, TIFFANY - UNIV. ARIZONA; GRONENBERG, WULFILA - UNIV. ARIZONA; Caseman, Delayne

Submitted to: Journal of Apicultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2008
Publication Date: 11/20/2008
Citation: Hoffman, G.D., Lucas, T., Gronenberg, W., Caseman, D.L. 2008. Brains and brain components in African and European honey bees (Hymenoptera: Apidae) - a volumetric comparison. Journal of Apicultural Research 47:281-285.

Interpretive Summary: We conducted a study that compared brain volume and the ability to associate an odor with a reward between European and African worker honey bees. We found that brain volume did not differ between the two races of bees, but an area of the brain called the mushroom bodies was significantly larger in the European workers. The mushroom bodies are a brain region associated with odor learning and memory formation. We found that a higher proportion of African workers than Europeans did not learn to associate odor with a nectar reward and this might be partially because of the differences in sizes of the mushroom bodies. In the European workers, those that were sampled in the hive and did not have foraging experience responded to odor and reward at the same frequency as foragers. However, African foragers required more exposure to odor being followed by reward before responding at levels that were comparable to house bees or to European bees. In the field, the differences between European and Africans in their response to odor might lead Africans to collect nectar from more frequently rewarding plants and translate into increased foraging efficiency.

Technical Abstract: A study was conducted to determine if the volume of major regions of the brain and the capacity for associative learning differed between European (AHB) and African honey bees (AHB). Associative learning was measured in 14-day old workers and foragers using proboscis extension response to odor-sugar water reward pairings. The brian volume of EHB and AHB workers was not significantly different, but the region comprising the mushroom body lobes was significantly larger in EHB. AHB differed in their response rates compared with EHB. In EHB, 14 day old workers and foragers responded at similar rates. In AHB though, foragers showed a lower initial learning score than their 14 day old sisters or to EHB foragers. The results suggest that with foraging experience AHB require more odor-reward pairings before responding then EHB, which might translate into a more conservative foraging strategy. Possible repercussions of the differences in behaviors between EHB and AHB foragers with respect to foraging efficiency are discussed.