L. bottom and clockwise: africanized honeybees at the UPR, Mayagüez Experimental Agricultural Station; africanized queen bee marked with a red dot; Tugrul Giray and undergraduate student Daliris Ramirez-Burgos demonstrate that these gentle africanized honeybees can be handled with little chance of being stung; Varroa destructor mites attacking a bee larva; bee damaged by mites. Middle: mites as seen under a microscope. Photos by Michael R. Elvin, Alberto Galindo-Cardona, Zachary Huang, José V.Camacho and Débora Weaver.
by Suzanna Engman
An entire colony of honeybees becomes sick and dies within a two-week interval. So far about half the honeybees in Europe and the United States have suddenly disappeared just so, and scientists are calling the phenomenon Colony Collapse Disorder (CCD). They theorize that a parasitic mite just a little larger than the period at the end of this sentence is partly responsible.
The Varroa destructor mite seems tiny to us, but if a bee were the size of a human, then the hemolymph-sucking, or blood-sucking, mite would be the size of a cat, says Tugrul Giray, Ph.D., a honeybee biologist and a professor of biology at the University of Puerto Rico, Río Piedras Campus. The mites weaken a bee’s immune system by making open wounds that are prone to infections. CCD is threatening european and United States honey production and crop pollination. European honeybees, bred for thousands of years for docility and kept by beekeepers in Europe and the United States, allow Varroa to sit on them and feed off their blood and that of their larvae. Their passive nature may be contributing to their demise.
Killer Bees
Africanized bees (Apis mellifera), a hybrid of african and european honeybees, escaped from Brazil in the late 1950s and spread throughout South and Central America, Mexico, and the Southwestern United States. The bees became known as “killer bees” because they tend to swarm more frequently and guard the hive more defensively, with a larger protected territory than european bees. European bees had been bred for docility and kept by beekeepers for honey production in Europe and the United States. In an effort to make european honeybees more adapted to tropical environments, biologist Warwick Kerr brought bees from Africa to Brazil in the 1950s and bred them with european bees. The story of the africanized bees’ escape has several versions. “One is that Warwick started giving beekeepers what he thought was already a gentle productive hybrid. Another version is that a beekeeper didn’t know what the excluder grates on the hives, which allowed the workers to pass freely but prevented the queens from escaping, were for and took them off. When he did that, several africanized queens escaped,” says UPR bee expert Tugrul Giray.
One reproductive female heads about 40,000 bees. The africanized queens mixed with local honeybee drones and retained the aggressive behavior of african bees. African bees are more defensive because they evolved to protect themselves against other insects and honey badgers that destroy hives. Also, in Africa the tradition of beekeeping was different from that in Europe, and docile colonies were not preferred. African and africanized bees are more likely to attack, and when they do, they attack more quickly, for a longer period of time, and in larger numbers than european bees. Scientists call this hyper-defensive behavior. Once a person is stung, a pheromone is released from a gland attached to the stinger, leading more bees to the victim. Although africanized bees’ venom is similar to that of european bees, africanized bees tend to sting their victims in greater numbers, resulting in more deaths than other subspecies.
On the other hand, some africanized bees (Apis mellifera) aggressively attack the mite. “Africanized bees in Puerto Rico actually go after the Varroa and bite it, cause damage, and dismember parts of it. When the Varroa attach to the bees, the bees start going crazy—turning and tossing around, trying to yank them off their bodies—and they are successful most of the time,” says Giray. Professor Giray and graduate students Bert Rivera-Marchand and Devrim Oskay observed this behavior in feral africanized bees, which now comprise almost all, if not all, of the feral honeybees in Puerto Rico. “In a study of mitochondrial DNA to identify maternity, we found that all feral and domesticated bees on the island are africanized.”
Researchers observe bee behavior in both the UPR, RP laboratory and in the 75 bee colonies at the UPR, Mayagüez Gurabo Experimental Agricultural Field Station. As graduate students, Rivera-Marchand and Oskay conducted field and lab assays for ectoparasite defensiveness. In the field, they opened the feral africanized bee larva cells of ten colonies to look for Varroa. Seven out of a thousand cells were infested. “In european colonies the infestation rate is about 10-20 percent. Here we’re finding less than 1 percent,” says Giray. To find out if adult feral bees are attacking the mites, researchers place a sticky piece of cardboard under the hive to collect Varroa that are groomed off the bees and then they observe the Varroa under the microscope. “Almost all of them, 94 percent, had damage, damage most likely done by bees.”
In the laboratory, the researchers put one Varroa on a petri dish with ten bees. “We see what happens upon first contact and analyze them for two minutes. We look at whether the Varroa tries to get on the bee, and if it does, whether the bee successfully protects itself from the Varroa. We observed unprovoked attacks from the africanized bees on these mites.
“Once we reported our observations to other scientists, they said they had observed the same behavior but it happened in one in 10,000 bees, a very rare event. In Puerto Rico, almost every feral bee shows this behavior.” And feral bee populations here are healthy and common. “It’s big news to find two or three feral colonies in the United States, whereas in Puerto Rico our estimated number is about 150,000 feral colonies.”
Africanized bees arrived in Puerto Rico in 1994, probably from Mexico or Texas, says Giray. But unlike other africanized bees, known popularly as “killer bees,” the bees in Puerto Rico are gentle, according to his laboratory team’s research, sponsored by National Science Foundation (NSF) and CATEC. “They’re not killer bees. Bert Rivera-Marchand, who completed his Ph.D. last year and is now assistant professor at InterAmerican University, Bayamón Campus, showed that bees in Puerto Rico are gentle africanized bees. Something has happened in Puerto Rico to make these bees less defensive.”
To test for defensive behavior, the researchers remove a comb from the bee colony and observe how aggressively bees respond. “Typically africanized bees, from Mexico for example, would, with no exception, run all over the cone, fall off it, and sting. Our bees here run a little bit on the combs, but they don’t fall off or fly up or attempt to sting.” The researchers also conduct sting tests. Protected by sting-proof clothing and netting, they disturb the colony and wave a leather flag in front of the colony to see how many bees attack the flag. “There are many zero responders, and the number of stings on the leather is similar to that of european honeybees.”
 Giray cites several possible causes for the gentle behavior. “One hypothesis is that there has been more mixing of european bees with the africanized bees on the island than in other places. Here you might have the introduction of africanized bees once, and not any further. Africanized bees in Puerto Rico have a large introgression, which means that they have a lot of european alleles, or genes, in their genome. We found that they are carrying 65-70 percent european genes, higher than any other population studied.” Elsewhere when the africanized bees mix with european bees, the african genes tend to dominate.
Another explanation for the gentle behavior is chance. “If you are on an island and have a reduced population or a population that comes only once, we may have received, just by chance, africanized bees that were gentle. There is variation within populations in Africa and also in Texas and Mexico. When you test them, some are really aggressive and others are not so bad in terms of defensiveness.”
CATEC has funded testing for the proposed hypotheses. Doctoral student Alberto Galindo Cardona is collaborating with graduate student Jenny Acevedo to test Rivera-Marchand’s hypothesis that africanized bees in Puerto Rico came from Mexico or Texas and have acquired a large percentage of european genes. In this study the researchers are likely to establish the source of the Puerto Rican bees with the help of “microsatellites,” sequences of DNA that consist of repeating units of one to four nucleotides. These markers show the extent of european genes in the africanized honeybee population from PR.
“We’re now completing a population genetics study of the bees in Puerto Rico. There are other questions. Even though we know the genetic part of the story, we want to know the behavioral part. For example, how frequently do africanized and european bees mate? In other countries, such as France, bee races remain separate, even though beekeepers bring them to the same location. It turns out that mating times of those bee races are different. By looking at the genetic data of bees in Puerto Rico, we predict that there is some overlap if not a complete overlap in mating behavior. This project will involve harmonic radar tracking technology, from our Canadian collaborators, and mini-transponders to be fitted on free flying individual bees,” says Giray.
“We have funding from NASA-PR Space Consortium, and Galindo just received a student research grant from the National Geographic Society/Waitts Grants Program for different aspects of this project. An undergraduate student, Rafine Moreno Jackson, received a NASA fellowship for her work as part of our bee transponder design team, and undergraduate Daliris Ramirez-Burgos was accepted to the NSF-REU program at the University of Central Oklahoma. She’ll visit Greece, Turkey (Bursa and Ankara), and Cyprus as part of her research project on bees.” In the last eight years, Giray has received $600 thousand from NSF and $1 million from NIH to study bee behavior. Science and health agencies fund the research because bees provide a promising model for studies in longevity, learning, and memory that could be applied to humans.
Unlike other places where honey production is down because of CCD, in Puerto Rico it is rising. “Currently there are about 130 beekeepers known to the Department of Agriculture, and production is about 14,000 gallons annually. From 2000 to 2007 honey production has grown four to five times. But still 14,000 gallons is less than seven percent of what is consumed in Puerto Rico. There is room to grow. Also if we know more about our bees, Puerto Rico may export them to other places for both honey production and pollination.”
tgiray2@yahoo.com
Bee Facts
- Alrededor de 20,000 especies de abejas han sido identificadas. Solo los miembros de la especie Apis son abejas melíferas.
- La especie Apis mellifera es utilizada para la polinización comercial de cultivos. El ochenta por ciento de los cultivos en EE.UU. (una industria de miles de millones de dólares) depende de la polinización de abejas.
- Las abejas pueden ver luz ultravioleta, a diferencia de los humanos, pero son incapaces de ver luz roja.
- La abeja reina es más grande que otras abejas y puede vivir hasta 47 veces más que lo normal. Los científicos estudian esto y tratan de aplicar sus hallazgos a los humanos.
- Las abejas, insectos sociales, son utilizadas como un sistema modelo en investigaciones evolutivas para comprender el comportamiento humano.
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El ácaro Varroa destructor puede ser el responsable de las alas deformes de las abejas melíferas, vistas en la fotografía, y se sospecha que también es responsable del fenómeno conocido como el Problema de Colapso de Colonias (CCD). Foto por Michael R. Elvin.
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