KILLER BEES / AFRICANIZED BEES
Dr. E. F. Legner, University of California, Riverside
Hybridized honeybees, or "killer bees" as they frequently are called, invaded the United States from Mexico. They crossed the border into south Texas in 1992, and gradually spread through the Southwest, appearing in California in 1995, a couple of years later than was originally predicted (see Taylor 1985 and Legner 1989c).
Public health problems may now be expected as people become aware of these bees and succumb to their attacks. However, studies on hybridized honeybee behavior at higher latitudes in South America suggest that the public health threat is not as great as these bees' notoriety (Taylor 1985). Just how far north they will travel is uncertain, but recent data from South America suggests that their range might not exceed Riverside=s 34E Lat. due to day-length influences. Nevertheless, museums and public agencies in California will undoubtedly be called upon for information about how to deal with the bees and perhaps to exterminate feral colonies. As of Spring 2005, Africanized bees have largely replaced the long in residence Italian strains in southern California. The new colonizers demonstrate a higher degree of inquisitiveness especially around food sites such as hummingbird feeders. In fact they mimic hummingbird behavior somewhat by buzzing the people who regularly replace the nutrients in the feeders when fermentation ahs reached a point where these are no long suitable for feeding.
Killer bees were originally purposely bred by scientists in one of the leading honeybee research laboratories of the world in Brazil in an effort to create a type that possessed superior foraging ability and honey production. Honey bee strains from Europe and southern Africa were crossed in this effort. However, these experiments led ultimately to the creation of the killer bee strain instead.
Most of the characteristics that distinguish killer bees from the original European stock, such as aggressiveness, early‑day mating times, degrees of pollen and honey hoarding, etc., are thought to be quantitative and, therefore, under the control of polygenic systems. Unfortunately, because of difficulties inherent in studying quantitative traits in honeybees, knowledge of this phase of their genetics is scant. In fact, Taylor (1985) acknowledged that there is an overall limited understanding of honeybee genetics. Thus, we really cannot predict what will occur following hybridization of African and European strains because practically all opinions are being derived from their behavior in South America (Kerr et al. 1982, McDowell 1984, Rinderer et al. 1982, 1984, Taylor 1985). Perhaps some indications can be obtained from other groups of Hymenoptera.
A great deal of information about hymenopteran quantitative inheritance has been gathered recently from parasitic wasps in the genus Muscidifurax that attack synanthropic Diptera. For example, in Muscidifurax raptorellus Kogan & Legner, a South American species, traits for fecundity and other reproductive behavior are under the control of a polygenic system (Legner 1987b, 1987a, 1988b, 1989a). Males in this species are able to change the female's oviposition phenotype and the aggressiveness of their larval offspring upon mating by transferring an unknown substance capable of evoking behavioral changes. It appears as if a proportion of the genes in the female have the phenotypic plasticity, or norm of reaction, to change expression under the influence of the male substance environment. The intensity of this response is different, depending on the respective genetic composition of the mating pair (Legner 1989a). Thus, the genes involved, which regulate phenotypic changes in the mated female, cause partial expression of the traits they govern shortly after insemination and before being inherited by resulting progeny. Such genes that are capable of phenotypic expression in the mother and her immature offspring have been called "Wary genes" because of their partial expression in the environment before maturity.
In the process of hybridization, wary genes are thought to quicken the pace of evolution by allowing natural selection to begin to act in the parental generation and on immature individuals (Legner 1987a, 1989a, 1993). Wary genes, which are detrimental to the hybrid population, might thus be more prone to elimination, and beneficial ones may be expressed in the mother before the appearance of her adult offspring.
If such a system prevails in honeybees, greater importance could be placed on drones because it may be possible for African or European drones to convey directly to unmated queens of either strain some of their own characteristics. The rapid domination of the African type in bee colonies in South and Central America could be explained partly by this process, although early‑day mating of African drones has been considered primarily responsible (Taylor 1985).
It is admittedly presumptuous at this time to infer similarities in the genetics of genera Apis and Muscidifurax, and the presence of wary genes in both. Some speculation seems justified where similarities might exist, however, especially as there is general agreement that permanent control of the killer bees will probably involve genetic manipulation and mating biology (The Calif. Bee Times 1988). If they are present, wary genes could offer a means to the abatement of this potentially severe public health pest. However, the possible occurrence of similar hybridization events in honeybees, as has been observed in Muscidifurax, would dictate extreme caution in setting into motion any processes that might lead to the formation of new strains. Available means for identifying hybridized colonies and eliminating queens that possess the most aggressive characteristics (Page & Erickson 1985, Taylor 1985) are tedious and imperfect. With the understanding that hybridization events and wary genes of the kind found in Muscidifurax have yet to be substantiated in Apis, the following suggestions for killer bee abatement are tentative.
Considerations for Deploying Wary Genes in Abatement.--Wary genes could be used to induce in queen bees and their offspring immediate changes in behavior such as aggressiveness, a reduced dispersal tendency, greater susceptibility to winter cold, lower fecundity, or even a preference for subsequent matings to occur in the afternoon when European drones are most active.
Killer bee queens that mate with different strains of European drones might exhibit immediate postmating depression in some cases, as was reported recently in some species of Muscidifurax (Legner 1988c). However, the offspring of crosses between African queens and certain strains of European drones might be expected to show hybrid vigor, expressed as increased fecundity and stamina, while other crosses involving different strains of European bees might produce a negative effect. Crosses between hybrid queens and hybrid males could result in superactive queens after mating, followed by even more highly active progeny, as was observed recently in M. raptorellus (Legner 1989d).
Selection favoring the superactive hybrids would tend to guarantee the survival of both parental strains and a continuous formation of hybrid bees, as has been suggested for Muscidifurax (Legner 1988c). Such a process could direct events leading to the relatively rapid evolution of a new strain. A superiorly adapted strain might displace killer bees and prevail in the area. Of course this strain also would have to display desirable characteristics of honey production, pollination, and nonaggression to be acceptable.
Mating European queens with strains of drones from feral northern European populations might cause such queens to acquire increased winter tolerance and give rise to hybrids that have even greater tolerances. On the other hand, having drones available that possess a reduced winter tolerance, could increase winter kill.
The selection of appropriate populations for intra specific crosses is critical to avoid detrimental outcomes from negative heterosis, or hybrid dysgenesis, as well as undesirable positive heterotic behavior, such as increased aggressiveness. Preintroduction assessments are essential to reveal such tendencies (see Legner 1988c, 1989c).
The introduction of alien genes into a population by hybridization utilizing naturally evolved parental populations, would probably be less risky than introducing genetically engineered ones where no natural selection has acted priorly. Researchers, working to inject laboratory‑engineered products into natural populations, should consider what kind of behavior will be demonstrated once heterosis has had a chance to act. Unless the engineered populations can be completely isolated reproductively from resident, wild populations, there is considerable risk involved.
There are many other possibilities. However, the first step should involve a more thorough understanding of honeybee genetics, and whether or not enough similarity exists with known hymenopteran systems to derive safe and viable strategies. Certain aspects of genetics are as yet unclear in Hymenoptera, which was demonstrated recently with the discovery of paternal influences in males (Legner 1989b). However, there is a clear rationale for preintroduction assessments as presently advocated for parasitic Hymenoptera (Coppel & Mertins 1977, Legner 1986, 1988c).
References: [Also see MELVYL Library]
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