The Relative Success of Africanized and European Honey-Bees Over a Range of Life-Zones in Costa Rica

The reproductive success and biology of Africanized and European honey-bees (Apis mellifera) were compared for a year over three life-zones from 900 m to 2800 m in Costa Rica, with the aim of identifying the factors which might limit the distribution of both bee types in tropical highlands. ' 2. Determinations of colony success and comparative biology included survivorship during the rainy season, causes of colony mortality, frequency of swarming, absconding, seasonal patterns of weight gain, brood-rearing (worker and drone), and nectar and pollen storage. 3. There was a significant difference in survivorship during the rainy season between European colonies given supplemental feedings and those not so fed; however, there were no significant differences in survivorship between the fed and unfed Africanized colonies. 4. More European than Africanized colonies died from gradual weakening, and only Africanized colonies absconded. However, colony deaths and absconding occurred with approximately equal frequency over all elevations during the year. 5. Almost three times as many Africanized as European colonies swarmed over the year. Although the majority of swarms occurred in the dry season at the lowest apiary, both bee types issued swarms at the highest elevation. 6. Africanized colonies weighed significantly more and maintained significantly larger worker brood areas than European colonies across all elevations for most months of the year, except at 2800 m from March through June. 7. Africanized colonies reared more drones than European colonies, except during the dry season at the highest elevation. 8. There were no significant differences in pollen storage between bee types across all elevations for 10 months of the year, and there were no significant differences in nectar storage throughout the year. 9. The most pronounced differences between the bee types were observed in the lowlands, which accounts for the rapid population growth and range expansion of Africanized bees, and their displacement of European bees in these areas. 10. The differences between the bee types in the highlands (2200 m and 2800 m) were not as pronounced for any of the determinations, indicating that neither was better adapted than the other to the climatic and resource conditions of tropical highlands. Possible reasons for the similarities in survival and performance between the bee types in the highlands as well as the implications of these findings on the potential distribution of Africanized bees are discussed.