William L. Rubink

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

Abstract 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.

Pollen Foraging Response to Brood Pheromone by Africanized and European Honey Bees (Apis mellifera L.)

Abstract We examined the pollen foraging responses of Africanized and European honey bee colonies to hexane extractable compounds of Africanized and European larvae (brood pheromone). Brood pheromone was presented to broodless Africanized and European colonies equalized for numbers of bees, food stores and, empty comb space. The pheromone significantly increased the ratio of pollen to nonpollen foragers returning to colonies. There was no differential pollen foraging response to pheromone racial origin. European colonies in this study had a significantly higher proportion of pollen to nonpollen foragers entering colonies than did Africanized colonies for pheromone and control treatments. The proboscis extension response to sucrose was used to test the sensitivity to sucrose of eight Africanized (most similar to Apis mellifera scutellata Lepeletier) and six European colonies (most similar to Apis mellifera ligustica L.). Individual sensitivity to sucrose has been demonstrated as a neuro-sensory correlate of foraging behavior in European bees such that individuals that forage for pollen have lower response thresholds to sucrose than bees that forage for nectar. Africanized bees were significantly more likely to respond to lower concentrations of sucrose than European bees. We concluded that sucrose response threshold was a poor predictor for comparative foraging behavior of these races because the neuro-sensory systems of the two races may be differentially “tuned” by thresholds to defensive cues.

Spatial and Temporal Distribution and Nest Site Characteristics of Feral Honey Bee (Hymenoptera: Apidae) Colonies in a Coastal Prairie Landscape

Abstract We evaluated the distribution and abundance of feral honey bee, Apis mellifera L., colonies in a coastal prairie landscape by examining nest site characteristics, population trends, and spatial and temporal patterns in cavity use. The colony densities of up to 12.5 colonies per km2 were the highest reported in the literature for an area including both suitable and unsuitable patches of nesting habitat. The measured cavity attributes were similar to those reported from other areas. The time occupied and turnover indices provided useful information about cavity quality, although none of the measured cavity attributes were correlated with these indices. Unmeasurable cavity characteristics, such as cavity volume, may provide a better estimate of cavity quality. Spatial patterns existed in cavity use by the feral colonies, with the colonies showing an aggregated pattern of distribution throughout the study. Colony aggregations probably resulted from the distribution of resources, especially cavities. Two years after the arrival of Africanized honey bees, cavities used by Africanized and European colonies were aggregated in distribution. During what seemed to be a transition period, both Africanized and European colonies were randomly distributed. After that time, European colonies remained randomly distributed, whereas Africanized colonies were aggregated. Therefore, the invasion of Africanized honey bees seemed to fragment the existing European population, corresponding to a decrease in the overall number of European colonies in the study area.

Identification of Africanized Honey Bee (Hymenoptera: Apidae) Mitochondrial DNA: Validation of a Rapid Polymerase Chain Reaction-Based Assay

Abstract Polymerase chain reaction (PCR)-amplified mitochondrial DNA (mtDNA) assays have been used in studies of the Africanization process in neotropical feral and managed honey bee populations. The approach has been adopted, in conjunction with morphometric analysis, to identify Africanized bees for regulatory purposes in the United States such as in California. In this study, 211 Old World colonies, representing all known introduced subspecies in the United States, and 451 colonies from non-Africanized areas of the southern United States were screened to validate a rapid PCR-based assay for identification of Africanized honey bee mtDNA. This PCR-based assay requires a single enzyme digestion (BglII) of a single PCR-amplified segment of the cytochrome b gene. The BglII polymorphism discriminates the mitochondrial haplotype (mitotype) of Apis mellifera scutellata L. (ancestor of Africanized bees) from that of A. m. mellifera, A. m. caucasia, A. m. ligustica, A. m. carnica, A. m. lamarcki, A. m. cypria, A. m. syriaca, and some A. m. iberiensis, but not from that of A. m. intermissa and some A. m. iberiensis. Nonetheless, given the very low frequency (<1%) of African non-A. m. scutellata mitotype present before arrival of Africanized bees in the United States, cytochrome b/BglII assay can be used to identify maternally Africanized bees with a high degree of reliability.

Pollen Selection by Feral Honey Bee (Hymenoptera: Apidae) Colonies in a Coastal Prairie Landscape

Abstract The collection of pollen by honey bees (Apis mellifera L.) provides valuable pollination services for many plants and the protein necessary for brood and young worker development. We collected and identified pollen gathered by feral honey bee colonies living in tree cavities in a coastal prairie landscape over the duration of 1 yr. Specific objectives included evaluating overlap in pollen use between colonies throughout the year, examining the influence of the spatial locations of the colonies on overlap in pollen use, and describing general pollen collection patterns. The feral colonies collected a wide variety of pollen types. Anemophilous (wind pollinated) pollen types were important in the fall, but entomophilous (insect pollinated) pollen types were important for the remainder of the year. Herbaceous plants and shrubs provided pollen during the spring and early summer, trees in mid- to late summer, and herbaceous plants in the fall. The pollen sources used by the feral colonies also tended to be good nectar sources. Overlap in pollen use between colonies varied throughout the year. Pollen overlap was correlated with distance for some sampling periods and not others, probably because of the way colonies select resources and the flowering phenology in the study area.

Honey Bees (Hymenoptera: Apidae) of African Origin Exist in Non-Africanized Areas of the Southern United States: Evidence from Mitochondrial Dna

Abstract Descendents of Apis mellifera scutellata Lepeletier (Hymenoptera: Apidae) (the Africanized honey bee) arrived in the United States in 1990. Whether this was the first introduction is uncertain. A survey of feral honey bees from non-Africanized areas of the southern United States revealed three colonies (from Georgia, Texas, and New Mexico) with a diagnostic African mitochondrial DNA cytochrome b/BglII fragment pattern. To assess maternal origin of these colonies, we developed a primer pair for amplification of a cytochrome b fragment and sequenced using internal sequencing primers. Samples of the three reported honey bee colonies plus another 42 representing the 10 subspecies known to have been introduced in the United States were sequenced. Of the three colonies, the colonies from Texas and New Mexico matched subspecies of European maternal ancestry, whereas the colony from Georgia was of African ancestry. Contrary to expectations, the mitotype of the latter colony was more similar to that exhibited by sub-Saharan A. m. scutellata than to the mitotypes common in north African A. m. intermissa Maa or Portuguese and Spanish A. m. iberiensis Engel. This finding was consistent with anecdotal evidence that A. m. scutellata has been sporadically introduced into the United States before the arrival of the Africanized honey bee from South America.

Africanization of a feral honey bee (Apis mellifera) population in South Texas: does a decade make a difference?

Abstract The arrival to the United States of the Africanized honey bee, a hybrid between European subspecies and the African subspecies Apis mellifera scutellata, is a remarkable model for the study of biological invasions. This immigration has created an opportunity to study the dynamics of secondary contact of honey bee subspecies from African and European lineages in a feral population in South Texas. An 11‐year survey of this population (1991–2001) showed that mitochondrial haplotype frequencies changed drastically over time from a resident population of eastern and western European maternal ancestry, to a population dominated by the African haplotype. A subsequent study of the nuclear genome showed that the Africanization process included bidirectional gene flow between European and Africanized honey bees, giving rise to a new panmictic mixture of A. m. scutellata‐ and European‐derived genes. In this study, we examined gene flow patterns in the same population 23 years after the first hybridization event occurred. We found 28 active colonies inhabiting 92 tree cavities surveyed in a 5.14 km2 area, resulting in a colony density of 5.4 colonies/km2. Of these 28 colonies, 25 were of A. m. scutellata maternal ancestry, and three were of western European maternal ancestry. No colonies of eastern European maternal ancestry were detected, although they were present in the earlier samples. Nuclear DNA revealed little change in the introgression of A. m. scutellata‐derived genes into the population compared to previous surveys. Our results suggest this feral population remains an admixed swarm with continued low levels of European ancestry and a greater presence of African‐derived mitochondrial genetic composition.

Diurnal patterns of pollen collection by feral honey bee colonies in southern Texas, USA

Honey bees (Apis mellifera L.) collect pollen for brood and young worker development, and pollinate many crops and economically important plants. Pollen was collected from honey bees from six feral honey bee colonies in southern Texas during two time periods to evaluate diurnal patterns of pollen collection. Overall, the same pollen types tended to be collected throughout the day, however, the percentages differed depending upon the time of day. Honey bees from four of the six colonies collected predominant pollen types (> 45% of a sample). Honey bees from the two colonies which did not collect a predominant pollen type collected two or more secondary pollen types (1645% of a sample). Lamiaceae was the most prevalent pollen type collected during the early sampling period and an unknown tricolporate grain was the most collected pollen type during the late sampling period. However, honey bees from one colony primarily collected the unknown tricolporate grain during both sampling periods. Several factors probably contributed to these diurnal variations in pollen collection patterns. These include floral patterns of pollen availability, resource depletion and/or profitability, nutritional needs of honey bees and preferences of individual honey bee foragers.

Tissue specificity and development expression of hexokinase and africanized honey bee specific proteins in apis mellifera L. (Hymenoptera: apidae)

Abstract Four hexokinase loci were found in honey bees. The HK-1 locus with two alleles was found in pupae and in the head, thorax and abdomen of adults. HK-11, HK-12 and HK-13 were found only in the immature stages. HK-11 and HK-12 are monomorphic. Gene duplication is suggested for the polymorphic locus HK-13 with two-band homozygotes and four-band heterozygotes. The Africanized honey bee specific proteins were not found in the larval or pupal stage of Africanized honey bees. In the audlt, they were weakly present in the head, present in the thorax and absent in the abdomen.

A phoretic uropodid mite associated with honey bee swarms of northeastern Mexico

Abstract In a bait-hive survey of natural honey bee populations of central Tamaulipas state, Mexico, and South Texas, U.S.A., two Mexican, European-origin swarms were found to include phoretic deutonymphs of the family Uropodidae (Acari: Mesostigmata). Subsequently two Africanized honey bee swarms, captured in the state of Veracruz, were also found to harbor the mites. No adult mites were found. These are the first known instances of phoresy by this family of mites on Apis mellifera. Mites were attached on the pollen baskets of the bees with as many as 21 mites occurring per bee. The association reported here is most likely transitory; both bees and mites are essentially migrants exploiting the same habitats.