THE PROBLEM

Africanized Honey Bees
 

 In 1956, Dr. Warwick E. Kerr, an eminent Brazilian geneticist, imported honey bees from South Africa into southern Brazil as part of a honey bee breeding program.  European races of honey bees had been used for commercial beekeeping and were considered to be poorly adapted for the tropics.  African races of honey bees were known to be well adapted for tropical conditions but to have objectionable characteristics not found in European races, for example an extreme tendency to sting.  Dr. Kerr hoped to cross tropically adapted bees from Africa with the more gentle European races of bees already present in Brazil and select for the best qualities of each.  In other words, he wanted to select a tropically adapted bee that did not sting excessively.

 Unfortunately, the African bees mated (uncontrolled) with the other bees in the area and some colonies even escaped from the experimental hives.  By 1957 there was an established wild population of now "Africanized" honey bees near Sao Paulo, Brazil.  Since then, the wild population of honey bees has grown and Africanized bees have taken over South and Central America, Mexico, and parts of the United States.  Africanized bees were first detected in 1991 in South Texas and since that time have spread throughout the southern half  of Texas, the southern tier of counties in New Mexico, all of  Arizona, all of Southern California south of Los Angeles and extreme southern Nevada (Figure 1).  There is no evidence that they have yet reached northern limits of migration.  Moreover, there is clear  evidence of widespread hybridization between European and Africanized bees in these areas.

Figure 1.  Current distribution of Africanized Honey Bee in the United States
              (as of 5 April 1999).

 
Currently, there is no consensus on the mechanism of "Africanization".  Some researchers believe that Africanized bees represent a spreading, independent population of bees that is partially isolated, reproductively, from bees of European descent.  Others believe that Africanization is a gene flow phenomenon where the relative frequencies of different genes within populations change with time.  How we ultimately deal with the problem of Africanized bees will depend on how well we understand its process.

 The potential impact of Africanized honey bees on U. S. agriculture is a hotly debated topic.  Data for honey production and the pollination potential of Africanized honey bees compared with North American (primarily of European descent) honey bees are equivocal.  Likewise, there is a lack of consensus among researchers about the expected distribution of wild colonies of Africanized bees within North America.  Some believe that the distribution will be limited to southern regions of the United States, while others believe they will be distributed as far north as the Canadian border.  There is clear evidence, particularly in Arizona, that Africanized bees have almost totally displaced Feral European colonies.  This is due almost exclusively to the demise of European colonies caused by parasitic mites.

 There is one characteristic of Africanized bees that is not debated; they are very defensive.  It is this extreme defensive behavior that threatens the ruination of the beekeeping industry with $150 million annual profits, and will have a major impact on a large sector of agriculture.  There will be further impact on the queen and package bee industry, especially in California and Texas and on migratory beekeeping for crop pollination and honey production.

 The value of honey bee pollination to United States agriculture has been recently estimated at $20 billion.  The level of pollination service provided by the beekeeping industry is dependent upon mass transport of thousands of colonies of honey bees down our nations highways and through our cities.  This system of "bees on wheels" will not be feasible with Africanized bees because of the high potential public health risk, and the associated high cost of liability insurance, because  many states will restrict the entry of Africanized bees, and  because beekeepers simply will not be willing to make the necessary changes in management practices.

 There are many mites associated with honey bees, however, most are of no economic importance.  These mites live in honey bee colonies and feed on very small quantities of stored food or on the refuse of the colony.  However, some mites form parasitic relationships with honey bees and, as a consequence, have an economic impact.

 The five most economically important parasitic mites of honey bees are: Varroa jacobsoni (the Varroa mite), Euvarroa sinhai, Tropilaelaps clareae, Tropilaelaps koenigerum, and Acarapis woodi (the tracheal mite).  Varroa jacobsoni was first detected in the United States in 1987 and is widely distributed around the world, as is Acarapis woodi  which was first detected in the United States in 1984.  Both species have since spread to all contiguous 48 states.  These two mites represent a serious and immediate threat to the U.S. beekeeping industry and to U.S. Agriculture.

Varroa mites enjoy a near world wide distribution having been found on all continents and in over 20 countries. Tracheal mite infestations have been reported throughout Africa, the Americas, Asia, Australia and Europe.

Varroa is currently the most important pest of honey bees world-wide.  It is an obligate parasite of bees and feeds externally on the immature stages of workers and the male reproductives (drones).  Parasitized individuals may die or develop into weakened, crippled adults that are incapable of functioning normally.  Unfortunately, this parasite is not detectable in colonies of honey bees until there is a large number of mites present.  Without effective control methods infested colonies dwindle in population or die.

Figure 2.  A Varroa Jacobsoni female.

 Much research has been done on Varroa in Europe.  A number of chemical agents have been used effectively for control.  Currently there are two chemicals registered for use in the United States.  Without chemical treatment, infested colonies in Europe are doomed to die, however, equivocal results have been reported from South America.  In Argentina and Uruguay mortality of mite infested colonies is high while in Brazil and Paraguay larroa infestations apparently do not result in colony death, a point of considerable interest both for economic considerations and for understanding basic biology.  It has been suggested that Africanized honey bees may be somewhat resistant to Varroa infestation, however there is evidence to suggest that resistance to Varroa may occur naturally in other races of honey bees as well.

 The impact of Varroa on U.S. agriculture has been significant.  The number of managed colonies has been halved while feral populations have been cut by more than 90 percent.  The remaining  colonies with educed numbers of workers are not effective honey producers or pollinators.  However, sufficient data are not available with which we can assess the total impact.

 Another important consideration is the effect of Varroa on the production of male reproductives in populations, Varroa mites seriously reduce the numbers of drones produced by infested colonies.  Because of the mating behavior of bees, drone production is extremely important for any program designed to reduce the effects of Africanized bees in the U.S.  Queen honey bees mate with about 10 to 18 different drones while they fly at specific mating sites away from their colonies.  It is imperative that commercial beekeepers produce large numbers of drones with desirable characteristics to mate with queens in order to reduce the proportion of matings by undesirable Africanized drones.

The primary method of controlling varroa in the U.S. is the use of fluvalinate.  however,  reports of resistance of the mites to fluvalinate are increasing.  this emphasizes the need for developing not only new chemical controls for varroa, but also a need to develop alternative methods to control the mites.

 A final important consideration is that of contamination of the hive and hive products, especially beeswax, with miticides.  Beeswax is an important world commodity which may become contaminated with miticide residues.  There is a growing body of evidence that miticide contaminated wax used in the processes of queen rearing and the building of new comb for brood rearing is contributing to queen and colony viability problems.

The tracheal mite has been regarded a serious pest of honey bees in Europe and elsewhere because it is often associated with large, unexplainable numbers of dead honey bee colonies.  This mite lives in the respiratory system of honey bees and is believed to shorten the life expectancy of an infested bee.  A shortened life expectancy results in a smaller number of worker bees in a colony and lower colony productivity.  Currently, there is not a consensus of opinion about the economic impact of this pest.  Some areas of Europe have apparently experienced devastating results while in others it apparently is not a problem.  In South America there are reports that Africanized honey bees show a natural resistance to infestation.  There is a growing body of evidence that honey bees in the United States are becoming resistant to the tracheal mite, however beekeepers in some areas are experiencing severe losses.

Figure 3.  Acarapis woodi adult and an infested honey bee trachea.