Genotype-environment interactions in honeybee guarding behaviour

Honeybees have an age-based division of labour that is influenced by genetic variability for the tendency to perform specific tasks. Individuals in a honeybee colony comprise diverse genotypes and their interactions can influence task allocation. Colonies from an African race (Africanized honeybees, AHB, Apis mellifera scutellata Ruttner) usually produce a much stronger defensive response than do European races of honeybees (EHB), and these races may differ in how individuals are allocated to the tasks of guarding and stinging. We observed guarding behaviour in colony environments that varied in proportions of genotypes (AHB, EHB) and population size. In large colonies, AHB showed much greater guarding persistence (number of days guarding) than EHB; hybrids were intermediate. In another series of experiments, three families each of AHB and EHB were cofostered in colonies with different AHB: EHB ratios, then tested in large and small colonies. In colonies of both sizes, colony environment interacted with both famly and type (AHB or EHB) for propensity to guard. Individuals of both types guarded more persistently in large colonies, but family and type both interacted with environment. EHB were more likely to initiate guarding bouts in low-AHB colonies, but persistence did not change with environment. AHB were insensitive to effects of environment for the tendency to initiate guarding behaviour, but were more persistent in high-AHB environments. EHB and AHB may differ in how they allocate individuals to guarding. The positive reinforcement of behaviour that occurs in high-defensive environments and in large populations could cause a stronger stinging response through alarm pheromone recruitment. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Methods for Comparing Nutrients in Beebread Made by Africanized and European Honey Bees and the Effects on Hemolymph Protein Titers

Honey bees obtain nutrients from pollen they collect and store in the hive as beebread. We developed methods to control the pollen source that bees collect and convert to beebread by placing colonies in a specially constructed enclosed flight area. Methods were developed to analyze the protein and amino acid composition of the pollen and beebread. We also describe how consumption of the beebread was measured and methods used to determine adult worker bee hemolymph protein titers after feeding on beebread for 4, 7 and 11 days after emergence. Methods were applied to determine if genotype affects the conversion of pollen to beebread and the rate that bees consume and acquire protein from it. Two subspecies (European and Africanized honey bees; EHB and AHB respectively) were provided with the same pollen source. Based on the developed methods, beebread made by both subspecies had lower protein concentrations and pH values than the pollen. In general, amino acid concentrations in beebread made by either EHB or AHB were similar and occurred at higher levels in beebread than in pollen. Both AHB and EHB consumed significantly more of the beebread made by AHB than by EHB. Though EHB and AHB consumed similar amounts of each type of beebread, hemolymph protein concentrations in AHB were higher than in EHB. Differences in protein acquisition between AHB and EHB might reflect environmental adaptations related to the geographic region where each subspecies evolved. These differences could contribute to the successful establishment of AHB populations in the New World because of the effects on brood rearing and colony growth.     

A Comparative Study of Varroa Jacobsoni Reproduction in Worker Cells of Honey Bees (Apis Mellifera) in England and Africanized Bees in Yucatan, Mexico

The aim of this study was to investigate an underlying mechanism of the apparent tolerance of Africanized honey bees (AHB) to Varroa jacobsoni mites in Mexico. This was achieved by conducting the first detailed study into the mites' reproductive biology in AHB worker cells. The data was then compared directly with a similar study previously carried out on European honey bees (EHB) in the UK. A total of 1071 singly infested AHB worker cells were analyzed and compared with the data from 908 singly infested EHB worker cells. There was no significant difference between the number of mother mites dying in the cells (AHB = 2.0%, EHB = 1.8%); the mean number of eggs laid per mite (AHB = 4.86, EHB = 4.93); the number of mites producing no offspring (AHB = 12%, EHB = 9%); and developmental times of the offspring in worker cells of AHB and EHB. However, there was a major difference between the percentage of mother mites producing viable adult female offspring (AHB = 40%, EHB = 75%). This was caused by the increased rate of mite offspring mortality suffered by the first (male) and second (female) offspring in AHB worker cells. Therefore, only an average of 0.7 viable adult female offspring are produced per mite in AHB, compared to 1.0 in EHB.     

Field energetics and the estimation of pollen and nectar intake in the marsupial honey possum, Tarsipes rostratus, in heathland habitats of South-Western Australia

A method is described, based on the simultaneous turnover of both stable (¹⁸O) and radioactive isotopes (³H and ²²Na), whereby the daily nectar and pollen intake of free-ranging marsupial honey possums (Tarsipes rostratus) may be estimated. The field metabolic rate is measured using doubly labelled water and nectar intake is estimated independently from the measured water and sodium fluxes. The method assumes that free-water intake is negligible (but may be accounted for if not the case), that virtually all dietary sodium is derived from nectar rather than from pollen, and that the animals are in energetic balance over the period of measurement. These assumptions have been tested and found to be robust, except during periods of heavy rain when significant intakes of free-water were recorded. Leaching experiments with pollen grains suggest that less than 10% of the sodium ingested by honey possums is derived from pollen and calculations thus assumed a 90%:10% split between nectar and pollen. Nectar intake averaged 5.9 ± 0.6 ml · day⁻¹ and regressing nectar intake on daily change in body mass predicts an intake of approximately 7 ml · day⁻¹ nectar to maintain balance for a 9 g honey possum. Estimates of pollen intake averaged 660 ± 156 mg · day⁻¹ and a similar regression analysis of the data predicts that a daily intake of approximately 1 g pollen would be needed to maintain mass balance of honey possums. Estimated nectar and pollen intakes did not differ significantly between males and females, but nectar intake was higher in winter compared with dry periods of the year. The sugar content of nectar falls during winter, however, and the overall energy derived from nectar thus remains roughly constant. Estimates of pollen and nectar intake for individual animals were not significantly correlated, suggesting that honey possums forage selectively for these two food items. Accepted: 19 August 1999     

A SNP test to identify Africanized honeybees via proportion of ‘African’ ancestry

The honeybee, Apis mellifera, is the world's most important pollinator and is ubiquitous in most agricultural ecosystems. Four major evolutionary lineages and at least 24 subspecies are recognized. Commercial populations are mainly derived from subspecies originating in Europe (75–95%). The Africanized honeybee is a New World hybrid of A. m. scutellata from Africa and European subspecies, with the African component making up 50–90% of the genome. Africanized honeybees are considered undesirable for bee‐keeping in most countries, due to their extreme defensiveness and poor honey production. The international trade in honeybees is restricted, due in part to bans on the importation of queens (and semen) from countries where Africanized honeybees are extant. Some desirable strains from the United States of America that have been bred for traits such as resistance to the mite Varroa destructor are unfortunately excluded from export to countries such as Australia due to the presence of Africanized honeybees in the USA. This study shows that a panel of 95 single nucleotide polymorphisms, chosen to differentiate between the African, Eastern European and Western European lineages, can detect Africanized honeybees with a high degree of confidence via ancestry assignment. Our panel therefore offers a valuable tool to mitigate the risks of spreading Africanized honeybees across the globe and may enable the resumption of queen and bee semen imports from the Americas.     

Admixture in Africanized honey bees (Apis mellifera) from Panamá to San Diego,California (U.S.A.)

The Africanized honey bee (AHB) is a New World amalgamation of several subspecies of the western honey bee (Apis mellifera), a diverse taxon historically grouped into four major biogeographic lineages: A (African), M (Western European), C (Eastern European), and O (Middle Eastern). In 1956, accidental release of experimentally bred “Africanized” hybrids from a research apiary in Sao Paulo, Brazil initiated a hybrid species expansion that now extends from northern Argentina to northern California (U.S.A.). Here, we assess nuclear admixture and mitochondrial ancestry in 60 bees from four countries (Panamá; Costa Rica, Mexico; U.S.A) across this expansive range to assess ancestry of AHB several decades following initial introduction and test the prediction that African ancestry decreases with increasing latitude. We find that AHB nuclear genomes from Central America and Mexico have predominately African genomes (76%–89%) with smaller contributions from Western and Eastern European lineages. Similarly, nearly all honey bees from Central America and Mexico possess mitochondrial ancestry from the African lineage with few individuals having European mitochondria. In contrast, AHB from San Diego (CA) shows markedly lower African ancestry (38%) with substantial genomic contributions from all four major honey bee lineages and mitochondrial ancestry from all four clades as well. Genetic diversity measures from all New World populations equal or exceed those of ancestral populations. Interestingly, the feral honey bee population of San Diego emerges as a reservoir of diverse admixture and high genetic diversity, making it a potentially rich source of genetic material for honey bee breeding.     

Colonization history and population differentiation of the Honey Bees (Apis mellifera L.) in Puerto Rico

Honey bees (Apis mellifera L.) are the primary commercial pollinators across the world. The subspecies A. m. scutellata originated in Africa and was introduced to the Americas in 1956. For the last 60 years, it hybridized successfully with European subspecies, previous residents in the area. The result of this hybridization was called Africanized honey bee (AHB). AHB has spread since then, arriving to Puerto Rico (PR) in 1994. The honey bee population on the island acquired a mosaic of features from AHB or the European honey bee (EHB). AHB in Puerto Rico shows a major distinctive characteristic, docile behavior, and is called gentle Africanized honey bees (gAHB). We used 917 SNPs to examine the population structure, genetic differentiation, origin, and history of range expansion and colonization of gAHB in PR. We compared gAHB to populations that span the current distribution of A. mellifera worldwide. The gAHB population is shown to be a single population that differs genetically from the examined populations of AHB. Texas and PR groups are the closest genetically. Our results support the hypothesis that the Texas AHB population is the source of gAHB in Puerto Rico.     

Nectar properties of the sunbird-pollinated plant Impatiens sakeriana: A comparison with six other co-flowering species

Adaptations of the nectar traits in bird-pollinated flowers are amongst the most discussed aspects of floral evolution. In the case of sunbird-pollinated plants, data on nectar traits originate almost exclusively from the South African region and are very scarce for tropical Africa, where paradoxically the highest sunbird diversity occurs. Here we present a study on the nectar properties of a sunbird-pollinated plant, Impatiens sakeriana, growing in the West African mountains, including the nectar production, diurnal changes in the nectar standing crop, the nectar concentrations, the nectar volumes, total sugar amounts and sugar composition. Moreover we compare the nectar traits of I. sakeriana with six other co-flowering insect-visited plant species.Our results showed that many nectar properties, including high volume (approx. 38 μL in flowers unvisited by sunbirds), low sugar concentration (approx. 30% w/w) and high sucrose content (95%), are specific to I. sakeriana, compared to the insect-visited plants. These are in accordance with the most recent theory that nectar properties of the sunbird-pollinated plants are similar to those pollinated by hummingbirds.     

Amygdalin in almond nectar and pollen – facts and possible roles

 Nectar and pollen within flowers are usually the primary attractants to floral visitors. Chemical analysis of almond nectar and pollen in this study revealed that they contain the secondary compound amygdalin. Floral display often reflects pollinator characters, and almond flowers are accordingly designated as “bee flowers”. A previous study in Israel showed that when almonds bloom early in the season they attract honeybees, but later in the season the bees shift toward other species that start blooming. In this study, we offered honeybees sugar solutions containing various concentrations of amygdalin. These preference experiments revealed that in mid-summer bees were not selective, whereas early in the summer they were more discriminating, and consumed faster the sugar solutions with the lower amygdalin concentrations. Possible roles of amygdalin in almond nectar and pollen are discussed. Received September 10, 2002; accepted January 17, 2003 Published online: June 2, 2003     

Bees get a head start on honey production

Nectar concentration is assumed to remain constant during transport by honeybees between flowers and hive. We sampled crop contents of nectar foragers on Aloe greatheadii var. davyana, a major winter bee plant in South Africa. The nectar is dilute (approx. 20% w/w), but the crop contents of bees captured on flowers are significantly more concentrated. In returning foragers, the concentration increases further to 38–40%, accompanied by a volume decrease. The doubling of sugar concentration suggests that nectar is regurgitated onto the tongue and evaporated during foraging and on the return flight. Processing of the dilute nectar into honey thus begins early, aided by low ambient humidities. This has implications for honeybee thermoregulation, water balance and energetics during foraging, and for the communication of nectar quality to recruits.     

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.     

The influence of paternity on virgin queen success in hybrid colonies of European and African honeybees

When African honeybees, Apis mellifera scutellata, migrate into an area, substantial hybridization occurs with existing European bee populations. However, over time European traits disappear until the populations become predominantly or entirely African. European patrilineal traits could be lost when hybrid colonies raise virgin queens if African-patriline queens have a survival advantage during reproductive competition. We examined queen competition in observation colonies that contained an African (A) or European (E) matriline, and both patrilines. In colonies of either matriline, the virgin queens that survived the elimination process were those that emerged sooner, piped more, eliminated more rivals and received more vibration signals from workers. Hybrid queens had increased piping and vibration rates and greater fighting success than did purebred queens. However, the effects of hybridization were expressed differently in the two matrilines, resulting in significant matriline-by-patriline interactions. In the E-matriline colonies, African-patriline queens emerged sooner, piped more, killed more rivals, were vibrated at higher rates and were more likely to survive the replacement period than were their European-patriline sister queens. In contrast, in the A-matriline colonies, the behaviour of African- and European-patriline queens was highly variable, and the two queen types did not differ for any of the characters examined or the ability to survive the rival elimination period. Thus, African paternity potentially conveys a competitive advantage to queens of European maternity, which would contribute to the spread of African alleles and the loss of European traits in hybrid zones. Furthermore, we observed that vibration signals were produced predominantly by African-paternity workers. The vibration signal may influence the spread of African traits, and this effect may be mediated largely by the behaviour of African-paternity workers. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

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.     

Pollinator foraging behavior and pollen collection on the floral morphs of tristylous Pontederia cordata L.

Summary The foraging behavior of the pollinators of tristylous Pontederia cordata was studied to determine if differences in floral morphology would lead to preferential visitation of the floral morphs. Although nectar production is not different in the three floral morphs, differences in the production and size of pollen grains produced by the three anther levels results in the morphs offering variable amounts of resources to pollen-collecting insects. Bumblebees (Bombus spp.) and the solitary bee Melissodes apicata used P. cordata primarily as a nectar source and therefore did not seem to exhibit any morph preference. In contrast, honeybees visited flowers mainly for pollen and preferred to forage on long-level anthers of the short-and mid-styled morphs. An analysis of the composition of corbicular pollen loads indicated that, relative to the frequency of production in the population: 1) honeybees collected an excess of pollen from long-level anthers; 2) bumblebees collected the three types of pollen without any apparent preference; and 3) M. apicata preferentially collected pollen from the short-level anthers — presumably because their proboscides are modified by the presence of tiny hairs. The results suggest that P. cordata in Ontario is serviced by a diverse, unspecialized pollinator fauna which is not co-adapted to the tristylous floral polymorphism.     

Response of pollinators to the tradeoff between resource acquisition and predator avoidance

Although the behaviour of animals facing the conflicting demands of increasing foraging success and decreasing predation risk has been studied in many taxa, the response of pollinators to variations in both factors has only been studied in isolation. We compared visit rates of two pollinator species, hoverflies and honeybees, to 40 Chrysanthemum segetum patches in which we manipulated predation risk (patches with and without crab spiders) and nectar availability (rich and poor patches) using a full factorial design. Pollinators responded differently to the tradeoff between maximising intake rate and minimising predation risk: honeybees preferred rich safe patches and avoided poor risky patches while the number of hoverflies was highest at poor risky patches. Because honeybees were more susceptible to predation than hoverflies, our results suggest that, in the presence of competition for resources, less susceptible pollinators concentrate their foraging effort on riskier resources, where competition is less severe. Crab spiders had a negative effect on the rate at which inflorescences were visited by honeybees. This effect was mediated through changes in the foraging strategy of honeybees, and could, in principle, be reversed by increasing nectar productivity of inflorescences. Our study shows that both pollinator species responded simultaneously and differently to variations in food reward and predation risk, and highlights the importance of studying the foraging strategies of pollinators in order to fully understand how plant–pollinator interactions are established.     

Geographical overlap of two mitochondrial genomes in Spanish honeybees (Apis mellifera iberica)

Restriction enzyme cleavage maps of mitochondrial DNA from the Spanish honeybee, Apis mellifera iberica (Hymenoptera: Apidae), were compared with those from the European subspecies A. m. mellifera, A. m. ligustica, and A. m. carnica, and the African subspecies A. m. intermissa and A. m. scutellata. The mitochondrial DNA (mtDNA) of the two African subspecies can be distinguished by restriction fragment polymorphisms revealed by Hinf I digests. Two distinct mtDNA types were found among Spanish honeybees: a west European mellifera-like type, which predominates in the north of Spain, and an African intermissa-like type, which predominates in the south. Spain appears to be a region of contact and hybridization between the two subspecies A. m. intermissa and A. m. mellifera, which respectively represent African and west European honeybee lineages. This natural boundary between European and African honeybee populations in the Old World may provide a model for predicting the eventual outcome of the colonization of North America by introduced African honeybees.     

Flight machinery dimensions of honeybees, Apis mellifera

The flight muscles of different honeybee subspecies are known to have different allozymes of malate dehydrogenase (Mdh) which in turn are correlated with differences in mass-specific metabolic flight rate. Flight capacity is also affected by dimensional, morphological relationships of mass and area which allow an estimation of an “excess power index”. The dimensions of the flight machinery of honeybees (based on our own data) were coupled with the frequency distributions of Mdh (taken from the literature) to compare nine subspecies of African and nine European honeybees, Apis mellifera as miniature aircraft. The two groups differed significantly for five dimensions of flight machinery and in the distribution frequencies of Mdh phenotypes. In the African group, northern and southern subgroups occurred which significantly differed in body mass and excess power index, while flight engine and body mass varied proportionately. In the European group, wing surface was nearly constant but body mass and the thorax/body mass ratio varied significantly resulting in significantly differing wing loading values. The final excess power index (modified for allozyme phenotype) of the European bees reflected both flight machinery and allozymic differences. Mdh allozymic phenotype frequencies were correlated with the dimensional morphological components of the excess power index. As a group, the European subspecies of honeybees were 33% heavier and had 15% more wing surface area than the African group. However, the former have a thorax/body mass ratio of 0.45 and wing loading value of 0.48 against the latter's 0.53 and 0.35 respectively. This confers an advantage on the African group solely on the grounds of dimensions because there was proportionately less mass per unit area of wing surface and so lower lift requirement. The better engine to aircraft mass ratio provides greater power per unit mass in the African group taken as miniature aircraft. Differences in metabolic capacity associated with Mdh allozymes (taken from the literature) finally result in an excess power index that is 38% greater in the African than European subspecies of honeybees. Accepted: 22 December 1998     

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.     

A trade-off between the amount and distance of pollen dispersal triggered by the mixed foraging behaviour of Sephanoides sephaniodes (Trochilidae) on Lapageria rosea (Philesiaceae)

Nectar thieves may increase or decrease pollinator-mediated pollen flow and thus may have positive or negative effects on plant reproductive success. In temperate rainforests of South America, the hummingbird Sephanoides sephaniodes acts as both a pollinator and non-destructive nectar thief on Lapageria rosea. Although pollinators that also act as nectar thieves have the potential to significantly modify plant reproductive success, no previous study has addressed this. To determine how the mixed behaviour of S. sephanoides affects pollen flow, we experimentally exposed some flowers to nectar theft and excluded nectar thieves from other flowers. We then assessed pollen dispersal into the floral neighbourhood. Thieved flowers exported less pollen, but the pollen exported was transferred farther into the neighbourhood. Our findings indicate a trade-off between distance and amount of pollen flow.     

An analysis of the energetic reward offered by field bean (Vicia faba) flowers: Nectar,pollen, and operative force

Global consumption of crops with a yield that is dependent on animal pollinators is growing, with greater areas planted each year. However, the floral traits that influence pollinator visitation are not usually the focus of breeding programmes, and therefore, it is likely that yield improvements may be made by optimizing floral traits to enhance pollinator visitation rates. We investigated the variation present in the floral reward of the bee‐pollinated crop Vicia faba (field bean). We examined the genetic potential for breeding flowers with a greater reward into current commercial varieties and used bee behavioral experiments to gain insight into the optimal nectar concentration to maximize bee preference. There was a large range of variation in the amount of pollen and nectar reward of flowers in the genotypes investigated. Bee behavioral experiments using nectar sugar concentrations found in V. faba lines suggest that Bombus terrestris prefers 55% w/w sugar solution over 40% w/w, but has no preference between 55% w/w and 68% w/w sugar solution. We provide a first indication of the force required to open V. faba flowers. Our results provide a valuable starting point toward breeding for varieties with optimized floral reward. Field studies are now needed to verify whether the genetic potential for breeding more rewarding flowers can translate into higher yield and yield stability.