Apis mellifera scutellata (africanized bee)

Honey bees disperse readily by swarming frequently. During times of nectar abundance, reproductive swarms may disperse from old colonies every 6 weeks. New queens are produced prior to swarming and as soon as the virgin daughter queens are ready to emerge, the mother queen and approximately half the workers leave the parental nest to establish a new colony (Beekman et al., 2008). Throughout its range in the New World, the Africanized honey bee swarms more often than, and shows a great ability to displace, resident European honey bee colonies. It can advance at 100-300 miles (160-480 km) per year by colonizing existing hives or forming new hives in the wild (Kim and Oguro, 1999).  

  A. mellifera scutellata was accidentally released into the Brazilian countryside after being intentionally imported into Brazil to aid the honey industry (Pereira and Chaud-Netto, 2005). Within 50 years this race had colonized most of South America and all of Central America.  

  A. mellifera scutellata was intentionally introduced to Brazil in the 1950s to assist the honey industry because this subspecies was considered well-adapted to the climate of southern Brazil.

Whitfield et al. (2006) characterized A. mellifera in native and introduced ranges using single-nucleotide polymorphisms, indicating that A. mellifera originated in Africa and expanded into Eurasia at least twice. This resulted in populations in eastern and western Europe that are geographically close, but genetically distant. The authors report that a third expansion in the New World has involved the near replacement of previously introduced ‘European’ honey bees by descendants of more recently introduced A. mellifera scutellata. Their analyses revealed differential replacement of alleles derived from eastern versus western Europe, with admixture evident in all individuals. Oden (2001) presents evidence based on morphometric analyses and PCA, DCA and RDA of wing indexes and floral characteristics, in support of the theory that African honey bees belong to a number of subspecies, and thus should not be referred to as ‘African’ bees. Diniz et al. (2003), studying honey bee populations in Southern Brazil and Uruguay, used allozyme loci and mtDNA haplotypes to characterize the populations and define a possible transition area between Africanized and European honey bees. The distribution limit of African bee colonies, i.e. populations with the African mtDNA haplotype only and a high proportion of African genes as shown by allozyme analysis, is located in northern Uruguay, with a hybridisation zone farther south in Uruguay. Sereno et al. (2004) described the use of morphological traits to differentiate between Africanized, European and North African colonies of A. mellifera. Looking at 18 morphological variables of worker bees, they found that colonies from Spain, Madeira and North Africa form a homogenous morphological group, which differed from a group in beehives of Brazil and Portugal. Francoy et al. (2006) looked at morphometric differences in a single wing cell to evaluate the method for discrimination of A. mellifera racial types. Analysis of the results showed significant differences between commercial USA Italian bees (predominantly A. mellifera ligustica), German Carniolan bees (predominantly A. mellifera carnica) and Africanized honey bees (predominantly A. mellifera scutellata). In conjunction with morphometric analyses, Pinto et al. (2003) describe the procedure of mitochondrial DNA (mtDNA) assays to identify Africanized bees for regulatory purposes in the USA. Nielson et al. (2000) describes the use of a PCR-based mitochondrial genotype assay to discriminate between 4 mitotypes found in North, Central and South American honey bee racial groups. Also see Sheppard and Smith (2000) for a description of methods used to identify African-derived bees in the Americas.

The period from egg to adult is approximately 18.5 days for worker bees and 16 days for queens, and adult longevity is approximately 30 days for workers, 5-10 weeks for drones, and 1-3 years for queens. For more details on egg, larvae and pupae production in A. mellifera scutellata colonies in Mandirituba, Parana, Brazil, see Pegoraro et al. (2001). One queen can produce 1500 eggs a day, and when a queen mates with a drone, the fertilized egg becomes a female worker bee, whereas unfertilized eggs become male drones, and larvae develop into queens if they are fed large quantities of royal jelly, a very nutritious creamy white liquid consisting of hypopharyngeal and mandibular gland secretions. Colonies reproduce by frequent swarming, and one colony can result in 17 other colonies in a year. Human et al. (2007) reported that under queen right conditions in the field, A. mellifera scutellata worker bees exhibited greater ovarian development when feeding on aloe pollen than on sunflower pollen, but these results were not replicated in laboratory studies.

Africanized honey bees are limited to hot tropical and warm sub-tropical habitats with separate wet and dry seasons, in comparison to hot and cold seasons in cooler temperate areas. Temperate climatic restrictions seem to be a natural limit to the expansion of Africanized honey bees at latitudes of approximately 35-40°. Radloff and Hepburn (1999) reported on A. mellifera worker bees in South Africa and described three morphoclusters: an unnamed population at >1500 m altitude; bees considered to be A. mellifera scutellata x A. m. capensis hybrids; and A. m. scutellata surrounding the mountains at <1500 m altitude. High humidity is necessary for honey bee brood development and honey bees are very efficient at regulating the biophysical parameters of their hive according to the needs of the colony. However, Human et al. (2006), studying A. mellifera scutellata, suggested that regulation of humidity is adjusted within sub-optimal limits.

In pristine and fragmented Amazonian rainforest, tropical rain forest trees characteristically occur in low population densities and rely on animals for cross-pollination. However, Dick et al. (2003) studied pollen dispersal and found that in highly disturbed habitats, A. mellifera may expand genetic neighbourhood areas and so link fragmented and continuous forest populations. For example, Dinizia excelsa was found to thrive in pastures and forest fragments in Manaus, Brazil even in the absence of native pollinators, and A. mellifera scutellata was the predominant floral visitor in fragmented habitats, also replacing native insects in isolated pasture trees. Gene flow over 3.4 km was reported in pasture indicating the significance of this bee in possibly altering the genetic structure of remnant populations via frequent, long-distance gene flow (Dick, 2001).

A. mellifera scutellata is spreading throughout tropical and subtropical America, hybridizing with and for the most part replacing European honey bees (mainly Apis mellifera mellifera and Apis mellifera ligustica).   A. mellifera scutellata out-competes native pollinators when it invades their territory. In Mexico, human-induced disturbance lead to lower species richness of stingless bees, and where there was greatest anthropogenic disturbance there was a higher degree of dominance of A. mellifera scutellata (Cairns et al., 2005). The area with the most intact ecosystem had the highest diversity of stingless bees, and aggressive competitive behaviour was used by A. mellifera against stingless bees, indicating that the former are adopting new behaviour to better compete with dominant native pollinators.

Behavioural studies of A. mellifera scutellata have been undertaken with the aim of creating informed strategies for dealing with Africanized honey bees and educating the public (Mello et al., 2003). The removal of bee colonies and swarms in Sao Paulo, Brazil was positively correlated with average temperature and degree of insolation, and negatively correlated with relative humidity and rainfall, and it was shown to be likely that colonies nested in artificial constructions, whereas wandering swarms tended to nest in trees. Such results can be used to predict times of the year when people should be more alert for activity of the bees. State Agricultural Departments in the USA have been tracking and studying Africanized honey bees since their introduction, and in particular, the Utah Department of Agriculture and Food has been setting traps since 2003 as an early warning line (UDAF, 2008).

Public awareness facilitated by studies such as that by Mello et al. (2003) will hopefully lead to the removal of structures seen as potential nesting sites for the bees and avoidance of areas possibly harbouring swarms. Africanized bees are much more likely to attack to defend their colonies compared to European honey bees and attacks are provoked by vibration, noise or motion within 50 feet of the nest. Offending origins of such sounds include lawn mowers, leaf blowers and hedge trimmers, and the odour of freshly cut grass or citrus may also be a source of provocation. Animals and humans may be pursued for up to a quarter of a mile and bees remain agitated for up to 8 hours after disturbance (UDAF, 2008).

As Africanized honey bees move into more temperate conditions, their adaptation to tropical climates is less advantageous. They would not establish a domain in temperate conditions and thus their control status is deemed ‘minimal priority’. A control level of ‘medium priority’ is recommended for North America’s southern semi-tropical area (Ojar, 2002). Thoenes (2002) described four types of bee control service: reactive bee control; preventative bee control; nuisance bee control; and sting emergency control, which are in demand with the advent of A. mellifera scutellata becoming a pest in urban areas.

In apiculture, yearly re-queening of a hive ensures that beekeepers rear docile European honey bees (Apis mellifera) and not the aggressive Africanized honey bees (UDAF, 2008), and drone-flooding can also be used to maintain European bee stock. Large numbers of the common European honey bee are maintained in areas where commercially-reared queen bees mate, thus limiting mating opportunities between European queens and Africanized drones (Ojar, 2002). Beekeepers can also exterminate wild bee nests to protect their managed bees from resource competition (Ojar, 2002).

The ectoparasite Varroa destructor has been found on A. mellifera scutellata in Venezuela (Principal et al., 2004). However, using a honey bee-mite simulation model, Martin and Medina (2004) showed that the adult longevity of Africanized honey bees (21 days) requires >12 000 mites to kill a colony. Martin and Kryger (2002) found that in cells of A. mellifera scutellata workers, V. destructor produced 0.9 fertilized females per mother mite, which is equivalent to susceptible European honey bees, but greater than cells containing A. mellifera capensis worker pseudoclones (0.4). Increased mite mortality was the main factor causing low mite reproductive success in cells of pseudoclones. Male protonymphs and some mothers were trapped in the upper part of the cell due to the pseudoclone being 8% larger than their host and not due to their short development time. It was concluded that mite populations in A. mellifera scutellata and A. mellifera capensis honey bees in South Africa are expected to increase to levels seen in Europe and the USA. Cape honey bees (A. mellifera capensis) pose a threat to A. mellifera scutellata (Oldroyd, 2002) and commercial beekeeping of A. mellifera scutellata in north-eastern South Africa (Hepburn, 2001). They are socially parasitic and have caused dramatic losses in managed populations of A. mellifera scutellata when Cape honey bees were moved from southern to northern Africa in 1990 (Martin et al., 2002b). There is a concern that wild populations may also be affected. Based on their surveys of beekeeping areas and nature reserves, it was concluded that the latter may provide important refuges for wild populations of A. mellifera scutellata (Hartel et al., 2006). Mechanisms underlying the parasitism include the ability of A. mellifera capensis to activate their ovaries in host colonies and lay eggs that evade being killed by other workers (Martin et al., 2002a). Neumann et al. (2000) explored the role of reproductive dominance in hybrid colonies (A. mellifera scutellata and A. mellifera capensis) by thelytokous laying workers of A. mellifera capensis. Also see papers by Moritz (2002), Martin et al. (2002b) and Wossler (2002) for example, documenting A. mellifera capensis parasitism on A. mellifera scutellata.

Gervan et al. (2005) reported on the effects of a pheromone from the mandibles of A. mellifera queens. The queen mandibular pheromone (QMP) influences worker behaviour and physiology. The authors observed calming of colonies and a reduction in stings in the presence of synthetic QMP. Their experiments were carried out using A. mellifera ligustica, which showed decreased defensive behaviour after exposure to liquid QMP in colonies with queens. In the absence of queens, exposure to liquid QMP did not affect the number of stings, but there was a decrease in the number of guard bees. Synthetic lures of QMP had no effect on the colonies tested. Obviously, a method to control defensive behaviour would be important to handling Africanized honey bees. Traps and chemicals have been used in an attempt to control A. mellifera scutellata, but have proved inefficient.