Why are African honey bees and not European bees invasive? Pollen diet diversity in community experiments

We studied resource use and competition by varieties of a honey bee, Apis mellifera, through re-introducing European A. m. ligustica in experimental apiaries in a habitat ‘saturated’ by African (or hybrid African and European) honey bees that naturally colonized forest in the Yucatan Peninsula of Mexico. Over 171 pollen species comprised honey bee diets. The Morisita-Horn similarity index (highest similarity = 1.0) between the two honey bee races was 0.76 for pollen use and, from the average daily volume usage by colonies of each bee subspecies, 0.55 for taxon-specific intensity of use. Although using more plant species, the European bee specialized much more heavily on a few plants than did African honey bees. By re-analysis of pollen pellets collected by locally-adapted (Mexican) European honey bees for one year, at the same experimental sites and using the same pollen traps as our studies, before the arrival of invasive honey bees in S. Mexico, we infer that resident bees may respond to exotic honey bee competition by shifting flower choice and by increasing resource specialization. We also show that replicated, quantitative pollen analysis is a powerful tool that may be applied to understanding diet diversity of bees