The spread of Africanized honey bees across Central America has had a much smaller impact on native tropical bee species than scientists previously predicted, three long-term studies by a Smithsonian scientist have revealed. Entomologists initially feared that as colonies of aggressive “killer bees” moved into the tropics and became established, they would out-compete the less plentiful native solitary bees for food and cause a permanent drop in native bee numbers. Instead, the native bees have proven resilient in the face of increased competition for food, says David Roubik of the Smithsonian Tropical Research Institute in Panama.
Roubik’s findings are based on studies he conducted for 17 years each in tropical rainforests in French Guiana, Panama and the Mexican Yucatan. Observations were made and data collected by Roubik on native bees before, during and after African honeybees invaded each area.
In a recently published paper on research in the Yucatan, Roubik and colleague Rogel Villanueva-Gutiérrez of the College of the Southern Border, Mexico, found that when faced with competition by African honey bees the native bees simply switch their feeding to similar trees, shrubs and vines that flower at the same time as their first preferences. When Africanized bees crowded out the native bees and took over pollination of two plant families long favored by the native bees–the cashew and spurge families–the native bees simply shifted their feeding to other plants. A diversity of flowering plants in the rainforests afford native solitary bees alternate feeding choices–and they take advantage of them.
During the course of the Yucatan study, Roubik and Villanueva-Gutiérrez observed that natural disasters such as hurricanes and drought had a negative impact on native bee populations, but the “sustained presence of Africanized honey bees did not,” Roubik says. “It should be mentioned, that Africanized honey bees seldom or never skirmish with or show any aggression toward other foragers on flowers,” Roubik says.
One of the native plants in the Yucatan preferred by both native bees and African bees became more abundant due to enhanced pollination from the African bees, the scientists observed. The result, they found, was a rise in the abundance of solitary native bees.
In the Yucatan study the scientists determined which species of plant both native bees and the invasive bees were visiting by collecting pollen from the bees’ nests and hives and identifying the pollen to plant species. They also recorded the relative amounts of specific pollen in each sample to determine which flowers the bees were visiting most. They learned that pollen from more than 171 plant species comprised the pollen diets of the African honey bees, including all of the plants most important to the solitary native bees as food.
African honeybees were accidentally released in Brazil in 1957 and have been moving north since that time. Roubik cautions that native bees living in areas that have a lower diversity of flowers may be less resilient to invasions of African honeybees. “Basically we’re seeing ‘scramble competition,’ as native bee species replace a lost source of pollen with pollen from a related plant” Roubik says. “In areas with less biodiversity these solitary native bees would not have the same range of options.”
African honeybees were accidentally released in Brazil in 1957 and have been moving north since that time. Unlike the native solitary bees, African honeybees live in large colonies and make large amounts of honey from flower nectar.
Roubik cautions that native bees living in areas that have a lower diversity of flowers may be less resilient to invasions of African honeybees. “Basically we’re seeing ‘scramble competition,’ as native bee species replace a lost source of pollen with pollen from a related plant” Roubik says. “In areas with less biodiversity these solitary native bees would not have the same range of options.”