Genetic dominance and worker interactions affect honeybee colony defense

Colonies of honeybees (Apis mellifera L.) were established thatvaried in the proportions of their workers that were of Europeanand hybrid (Africanized x European) descent. Colony defensiveresponses increased with higher proportions of hybrid workers.Colonies consisting exclusively of hybrid workers did not differin their response from "pure" Africanized colonies, suggestingthat the strong defensive behavior of Africanized workers isgenetically dominant. European workers became more defensivein colonies that also contained hybrid workers, whereas hybridworkers became less defensive in the same mixed colonies. Inmixed colonies hybrid workers were individually more likelythan Europeans to sting a leather target but not more likelyto guard the entrance.     

Nest Defense Behavior in Colonies from Crosses Between Africanized and European Honey Bees (Apis mellifera L.) (Hymenoptera: Apidae)

Honey bee (Apis mellifera L.) colonies with either European or Africanized queens mated to European or Africanized drones alone or in combination were tested for defensive behavior using a breath test. The most defensive colonies were those with European or Africanized queens mated to Africanized drones. In colonies where both European and Africanized patrilines existed, most of the workers participating in nest defense behavior for the first 30 s after a disturbance were of African patrilines. Nest defense behavior appears to be genetically dominant in honey bees.     

Genetic variation in worker temporal polyethism and colony defensiveness in the honey bee, Apis mellifera

To test the hypothesis that colonies of honey bees composedof workers with faster rates of adult behavioral developmentare more defensive than colonies composed of workers with slowerbehavioral development, we determined whether there is a correlationbetween genetic variation in worker temporal polyethism andcolony defensiveness. There was a positive correlation for thesetwo traits, both for European and Africanized honey bees. Thecorrelation was larger for Africanized bees, due to differencesbetween Africanized and European bees, differences in experimentaldesign, or both. Consistent with these results was the findingthat colonies with a higher proportion of older bees were moredefensive than colonies of the same size that had a lower proportionof older bees. There also was a positive correlation betweenrate of individual behavioral development and the intensityof colony flight activity, and a negative correlation betweencolony defensiveness and flight activity. This suggests thatthe relationship between temporal polyethism and colony defensivenessmay vary with the manner in which foraging and defense dutiesare allocated among a colony's older workers. These resultsindicate that genotypic differences in rates of worker behavioraldevelopment can influence the phenotype of a honey bee colonyin a variety of ways.     

Quantitative trait loci for honey bee stinging behavior and body size.

A study was conducted to identify quantitative trait loci (QTLs) that affect colony-level stinging behavior and individual body size of honey bees. An F1 queen was produced from a cross between a queen of European origin and a drone descended from an African subspecies. Haploid drones from the hybrid queen were individually backcrossed to sister European queens to produce 172 colonies with backcross workers that were evaluated for tendency to sting. Random amplified polymorphic DNA markers were scored from the haploid drone fathers of these colonies. Wings of workers and drones were used as a measure of body size because Africanized bees in the Americas are smaller than European bees. Standard interval mapping and multiple QTL models were used to analyze data. One possible QTL was identified with a significant effect on tendency to sting (LOD 3.57). Four other suggestive QTLs were also observed (about LOD 1.5). Possible QTLs also were identified that affect body size and were unlinked to defensive-behavior QTLs. Two of these were significant (LOD 3.54 and 5.15).     

Suppression of queen rearing in European and Africanized honey beesApis mellifera L. by synthetic queen mandibular gland pheromone

Summary Queen rearing is suppressed in honey bees (Apis mellifera L.) by pheromones, particularly the queen's mandibular gland pheromone. In this study we compared this pheromonally-based inhibition between temperate and tropically-evolved honey bees. Colonies of European and Africanized bees were exposed to synthetic queen mandibular gland pheromone (QMP) for ten days following removal of resident queens, and their queen rearing responses were examined. Queen rearing was suppressed similarly in both European and Africanized honey bees with the addition of synthetic QMP, indicating that QMP acts on workers of both races in a comparable fashion. QMP completely suppressed queen cell production for two days, but by day six, cells containing queen larvae were present in all treated colonies, indicating that other signals play a role in the suppression of queen rearing. In queenless control colonies not treated with QMP, Africanized bees reared 30% fewer queens than Europeans, possibly due to racial differences in response to feedback from developing queens and/or their cells. Queen development rate was faster in Africanized colonies, or they selected older larvae to initiate cells, as only 1 % of queen cells were unsealed after 10 days compared with 12% unsealed cells in European colonies.     

Effects of meteorological factors on defensive behaviour of honey bees

The defensive behaviour of honey bee colonies (Apis mellifera L.) was quantitated in the field throughout a three month season by the use of a standardized test in which numbers of stings in a leather target were counted after single colonies were opened and exposed to alarm pheromone. The main results show how the defensive behaviour of honey bees is highly dependent on weather factors. Eliminating genetic variance, the following meteorological variables account for 92.4% of the variation in defensive behaviour: air temperature, solar radiation intensity, wind velocity, relative humidity, and barometric pressure.     

Genetic dissection of honeybee (Apis mellifera L.) foraging behavior

We demonstrate the effects of a new quantitative trait locus (QTL), designated pln3, that was mapped in a backcross population derived from strains of bees selected for the amount of pollen they store in combs. We independently confirmed pln3 by demonstrating its effects on individual foraging behavior, as we did previously for QTLs pln1 and pln2 (Hunt et al. 1995). QTL pln2 is very robust in its effects on foraging behavior. In this study, pln2 was again shown to affect individual foraging behavior of workers derived from a hybrid backcross of the selected strains. In addition, pln2 was shown to affect the amount of pollen stored in combs of colonies derived from a wide cross of European and Africanized honeybees. This is noteworthy because it demonstrates that we can map QTLs for behavior in interstrain crosses derived from selective breeding and study their effects in unselected, natural populations. The results we present also demonstrate the repeatability of finding QTLs with measurable effects, even after outcrossing selected strains, suggesting that there is a relatively small subset of QTLs with major effects segregating in the population from which we selected our founding breeding populations. The different QTLs, pln1, pln2, and pln3, appear to have different effects, revealing the complex genetic architecture of honeybee foraging behavior.     

The Africanization of honeybees (Apis mellifera L.) of the Yucatan: a study of a massive hybridization event across time

Until recently, African and European subspecies of the honeybee (Apis mellifera L.) had been geographically separated for around 10,000 years. However, human-assisted introductions have caused the mixing of large populations of African and European subspecies in South and Central America, permitting an unprecedented opportunity to study a large-scale hybridization event using molecular analyses. We obtained reference populations from Europe, Africa, and South America and used these to provide baseline information for a microsatellite and mitochondrial analysis of the process of Africanization of the bees of the Yucatan Peninsula, Mexico. The genetic structure of the Yucatecan population has changed dramatically over time. The pre-Africanized Yucatecan population (1985) comprised bees that were most similar to samples from southeastern Europe and northern and western Europe. Three years after the arrival of Africanized bees (1989), substantial paternal gene flow had occurred from feral Africanized drones into the resident European population, but maternal gene flow from the invading Africanized population into the local population was negligible. However by 1998, there was a radical shift with both African nuclear alleles (65%) and African-derived mitochondria (61%) dominating the genomes of domestic colonies. We suggest that although European mitochondria may eventually be driven to extinction in the feral population, stable introgression of European nuclear alleles has occurred.     

Africanized honey bees (Hymenoptera: Apidae) have a greater fidelity to sunflowers than European bees

A study of sunflower, Helianthus annuus L., pollen collection by Africanized and European honey bees, Apis mellifera L., was conducted in a hybrid seed production field in Argentina. Africanized honey bees collected significantly larger proportions of sunflower pollen than did European honey bees. The result suggests that Africanized bees would be more efficient for commercial sunflower seed production.     

Is the number of antennal plate organs (sensilla placodea) greater in hygienic than in non-hygienic Africanized honey bees?

Hygienic behavior is a desirable trait in honey bees (Apis mellifera L.), as hygienic bees quickly remove diseased brood, interrupting the infectious cycle. Hygienic lines of honey bees appear to be more sensitive to the odors of dead and diseased honey bee brood, and Africanized honey bees are generally more hygienic than are European honey bees. We compared the number of sensilla placodea, antennal sensory structures involved in the perception of odor, in 10 bees from each of six hygienic and four non-hygienic colonies of Africanized honey bees. The sensilla placodea of three of the terminal segments (flagellomeres) of the right antenna of each bee were counted with a scanning electron microscope. There were no significant differences in the mean numbers of sensilla placodea between the hygienic and non-hygienic bees, though the variance was higher in the hygienic group. Flagellomere 4 had significantly more sensilla placodea than flagellomeres 6 and 8. However, there was no significant difference between the other two flagellomeres. As hygienic bees are capable of identifying dead, injured, or infested brood inside a capped brood cell, sensilla placodea probably have an important role in enabling worker bees to sense sick brood. However, we did not find greater numbers of this sensory structure in the antennae of hygienic, compared to non-hygienic Africanized honey bees.     

The influence of brood comb cell size on the reproductive behavior of the ectoparasitic mite Varroa destructor in Africanized honey bee colonies

Africanized honey bees (Apis mellifera, Hymenoptera: Apidae) in Brazil are tolerant of infestations with the exotic ectoparasitic mite, Varroa destructor (Mesostigmata: Varroidae), while the European honey bees used in apiculture throughout most of the world are severely affected. Africanized honey bees are normally kept in hives with both naturally built small width brood cells and with brood cells made from European-sized foundation, yet we know that comb cell size has an effect on varroa reproductive behavior. Three types (sizes) of brood combs were placed in each of six Africanized honey bee colonies: new (self-built) Africanized comb, new Italian comb (that the bees made from Italian-sized commercial foundation), and new Carniolan comb (built naturally by Carniolan bees). About 100 cells of each type were analyzed in each colony. The Africanized comb cells were significantly smaller in (inner) width (4.84 mm) than the European-sized comb cells (5.16 and 5.27 mm for Italian and Carniolan cells, respectively). The brood cell infestation rates (percentage cells infested) were significantly higher in the Carniolan-sized comb cells (19.3%) than in the Italian and Africanized cells (13.9 and 10.3%, respectively). The Carniolan-sized cells also had a significantly larger number of invading adult female mites per 100 brood cells (24.4) than did the Italian-sized cells (17.7) and the natural-sized Africanized worker brood cells (15.6). European-sized worker brood cells were always more infested than the Africanized worker brood cells in the same colony. There was a highly significant correlation (P<0.01) between cell width and the rate of infestation with varroa in four of the six colonies. The small width comb cells produced by Africanized honey bees may have a role in the ability of these bees to tolerate infestations by Varroa destructor, furthermore it appears that natural-sized comb cells are superior to over-sized comb cells for disease resistance.     

The influence of hybridization between African and European honeybees, Apis mellifera, on asymmetries in wing size and shape

Abstract We examined the possible role of hybridization in the invasion process of the African honeybee by testing two hypotheses regarding fluctuating asymmetry (FA), a measure of developmental stability, in wing characteristics: (1) FA should be higher in hybrid versus parental genotypes of African and European races; (2) FA should be lower in African bees compared to hybrid and European workers. Parental and reciprocal hybrid worker genotypes were cross fostered in common-hive rearing environments. We did not find greater FA for wing size and shape in the hybrids compared to both parental types. However, we did find significantly lower FA of shape in the African workers compared to the European and hybrid workers, suggesting that European bees and their hybrids may have compromised fitness relative to African bees. We also found that the two hybrid genotypes significantly differed in overall wing size and shape. If these differences affect wing aerodynamics, then the paternity of hybrids may influence worker performance and could potentially contribute to the loss of European matrilines. Hybridization had few consistent effects on directional asymmetry for wing size and shape. Genotypic factors played a far greater role in determining the effect of hybridization on wing morphology than did differences in rearing environment. Thus, African bees may have lower FA for wing shape (and by inference greater developmental stability) relative to European and hybrid workers, which may contribute to the ability of African bees to displace European honeybee races in invaded regions.     

Range and Frequency of Africanized Honey Bees in California (USA)

Africanized honey bees entered California in 1994 but few accounts of their northward expansion or their frequency relative to European honey bees have been published. We used mitochondrial markers and morphometric analyses to determine the prevalence of Africanized honeybees in San Diego County and their current northward progress in California west of the Sierra Nevada crest. The northernmost African mitotypes detected were approximately 40 km south of Sacramento in California’s central valley. In San Diego County, 65% of foraging honey bee workers carry African mitochondria and the estimated percentage of Africanized workers using morphological measurements is similar (61%). There was no correlation between mitotype and morphology in San Diego County suggesting Africanized bees result from bidirectional hybridization. Seventy percent of feral hives, but only 13% of managed hives, sampled in San Diego County carried the African mitotype indicating that a large fraction of foraging workers in both urban and rural San Diego County are feral. We also found a single nucleotide polymorphism at the DNA barcode locus COI that distinguishes European and African mitotypes. The utility of this marker was confirmed using 401 georeferenced honey bee sequences from the worldwide Barcode of Life Database. Future censuses can determine whether the current range of the Africanized form is stable, patterns of introgression at nuclear loci, and the environmental factors that may limit the northern range of the Africanized honey bee.     

The influence of nest site selection on the population dynamics of Africanized honey bees in an urban landscape

Urban landscapes provide habitat for many species, including domesticated and feral honey bees, Apis mellifera L. (Hymenoptera: Apidae). With recent losses of managed honey bee colonies, there is increasing interest in feral honey bee colonies and their potential contribution to pollination services in agricultural, natural, and urban settings. However, in some regions the feral honey bee population consists primarily of Africanized honey bees. Africanized honey bees (AHB) are hybrids between European honey bees and the African honey bee, Apis mellifera scutellataLepeletier, and have generated economic, ecological, and human health concerns because of their aggressive behavior. In this study, we used two long‐term datasets (7–10 years) detailing the spatial and temporal distribution of AHB colonies in Tucson, AZ, USA, where feral colonies occupy a variety of cavities including water meter boxes. A stage‐structured matrix model was used to elucidate the implications of nest site selection and the effects of colony terminations on the structure and dynamics of the AHB population. Our results suggest that Tucson's AHB population is driven by a relatively small number of ‘source’ colonies that escape termination (ca. 0.165 colonies per km² or 125 colonies in total), although immigrating swarms and absconding colonies from the surrounding area may have also contributed to the stability of the Tucson AHB population. Furthermore, the structure of the population has likely been impacted by the number and spatial distribution of water meter boxes across the city. The study provides an example of how urban wildlife populations are driven by interactions among landscape structure, human management, and behavioral traits conferred by an invasive genotype.     

Quantitative trait loci influencing honeybee alarm pheromone levels.

Quantitative trait loci (QTL) mapping procedures were used to identify loci that influence the levels of alarm pheromones found in the stinging apparatus of worker honeybees. An F1 queen was produced from a cross between a queen of European origin and a drone descended from an African subspecies. Haploid drones from the hybrid queen were individually backcrossed to European queens to produce 172 colonies. Samples of stings were taken from backcross workers of these colonies. Alarm pheromone levels were determined by gas chromatography. RAPD markers were scored from the haploid drone fathers of these colonies. The multiple-QTL model (MQM) of MapQTL was used to identify QTLs that influence the levels of four alarm pheromone components. Seven independent, potential QTLs were identified with LOD scores greater than two, and one at LOD 1.88. We identified one QTL for n-decyl acetate, three for n-octanol, four for isopentyl acetate, and one for hexyl acetate. One region of linkage group XI shows a strong influence on body size and the levels of three alarm pheromone components. This locus explained 40% of the variance for the amount of n-decyl acetate (LOD 6.57). In general, the QTLs influencing alarm pheromone levels were independent of previously identified loci that influenced the stinging behavior of these colonies. The only exception was a potential locus influencing levels of n-octanol, which was inversely correlated with stinging behavior.     

Nocturnal defensive responses of Africanized and European honey bees to the greater wax moth (Galleria mellonella L.)

Colonies of honey bees (Apis mellifera L.) in Brazil, the United States and Venezuela were presented with adult greater wax moths (Galleria mellonella L.) at their hive entrances. Africanized colonies were quicker, more persistent, and more intense in their attacks than were European colonies. Both races attacked female moths in preference to males. Although colony size did not appear to be related to defensiveness, attack data were correlated with the numbers of bees guarding the entrance. Africanized colonies had significantly more guard bees. During successive trials, both races attacked the moths in significantly shorter times. These findings may help explain the unexpectedly low population levels of G. mellonella in some areas of South America.     

Uncapping activity of Apis mellifera L. (Hymenoptera: Apidae) towards worker brood cells infested with the mite Varroa destructor Anderson & Treuman (Mesostigmata: Varroidae)

Varroosis, a disease caused by the mite Varroa destructor Anderson and Treuman has killed hundreds of thousands of Apis mellifera L. colonies in various parts of the world. Nevertheless, the damage caused by this mite varies with the type of bee and climate conditions. Varroa causes little damage to Africanized bee colonies in Brazil, as the infestation rates are relatively stable and low. We evaluated the hygienic behavior (uncapping and removal of brood) of highly hygienic Africanized bees using combs with worker brood cells infested (naturally) and no infested with V. destructor. The daily uncapping rate, measured in eight colonies during six days, was 3.5 fold higher in the combs infested with varroa compared to no infested combs. The results show that the Africanized bees are able to recognise and remove brood cells naturally infested with V. destructor what is an important mechanism for tolerance against varroa.     

Temporal pattern of africanization in a feral honeybee population from Texas inferred from mitochondrial DNA

The invasion of Africanized honeybees (Apis mellifera L.) in the Americas provides a window of opportunity to study the dynamics of secondary contact of subspecies of bees that evolved in allopatry in ecologically distinctive habitats of the Old World. We report here the results of an 11-year mitochondrial DNA survey of a feral honeybee population from southern United States (Texas). The mitochondrial haplotype (mitotype) frequencies changed radically during the 11-year study period. Prior to immigration of Africanized honeybees, the resident population was essentially of eastern and western European maternal ancestry. Three years after detection of the first Africanized swarm there was a mitotype turnover in the population from predominantly eastern European to predominantly A. m. scutellata (ancestor of Africanized honeybees). This remarkable change in the mitotype composition coincided with arrival of the parasitic mite Varroa destructor, which was likely responsible for severe losses experienced by colonies of European ancestry. From 1997 onward the population stabilized with most colonies of A. m. scutellata maternal origin.     

Parental Analysis of Introgressive Hybridization between African and European Honeybees Using Nuclear DNA Rflps

African honeybees, introduced into Brazil 33 years ago, have spread through most of South and Central America and have largely replaced the extant European bees. Due to a paucity of genetic markers, genetic interactions between European and African bees are not well understood. Three restriction fragment length polymorphisms (RFLPs), detected with random, nuclear DNA probes, are described. The polymorphisms are specific to bees of European descent, possibly specific to certain European races. Each European marker was found present at a high frequency in U.S. colonies but absent in South African bees. Previous mitochondrial DNA studies of neotropical bees have revealed negligible maternal gene flow from managed European apiaries into feral African populations. The findings reported here with nuclear DNA show paternal gene flow between the two but suggest asymmetries in levels of introgressive hybridization. Managed colonies in southern Mexico, derived from European maternal lines, showed diminished levels of the European nuclear markers, reflecting significant hybridization with African drones. The European alleles were present only at low frequencies in feral swarms from the same area. The swarms were of African maternal descent. In Venezuelan colonies, also derived from African maternal lines, the European markers were almost totally absent. The results point to limited paternal introgression from European colonies into the African honeybee populations. These findings dispute other views regarding modes of Africanization.     

Africanization in the United States: replacement of feral European honeybees (Apis mellifera L.) by an African hybrid swarm

The expansion of Africanized honeybees from South America to the southwestern United States in <50 years is considered one of the most spectacular biological invasions yet documented. In the American tropics, it has been shown that during their expansion Africanized honeybees have low levels of introgressed alleles from resident European populations. In the United States, it has been speculated, but not shown, that Africanized honeybees would hybridize extensively with European honeybees. Here we report a continuous 11-year study investigating temporal changes in the genetic structure of a feral population from the southern United States undergoing Africanization. Our microsatellite data showed that (1) the process of Africanization involved both maternal and paternal bidirectional gene flow between European and Africanized honeybees and (2) the panmitic European population was replaced by panmitic mixtures of A. m. scutellata and European genes within 5 years after Africanization. The post-Africanization gene pool (1998-2001) was composed of a diverse array of recombinant classes with a substantial European genetic contribution (mean 25-37%). Therefore, the resulting feral honeybee population of south Texas was best viewed as a hybrid swarm.