Apis Mellifera Unicolor Research Articles

Parasite and virus dynamics in the honeybee Apis mellifera unicolor on a tropical island recently invaded by Varroa destructor

In La Réunion, the established honeybee subspecies Apis mellifera unicolor, an endemic subspecies of African lineage, is facing considerable challenges. Since the introduction of the Varroa destructor mite in 2017 high colony losses have been recorded. We investigated the dynamics of V. destructor and two viruses, the Deformed Wing Virus (DWV), known to be transmitted by the mite, and the Chronic Bee Paralysis Virus (CBPV), in A. m. unicolor. Colonies from two apiaries located at 300 and 900 m a.s.l were monitored twice for one year without any acaricide treatment. The brood area, V. destructor infestation rates, DWV and CBPV prevalence and load were recorded monthly. A. m. unicolor maintained brood rearing throughout the year. Varroa destructor infestation resulted in high colony mortality (up to 85 %) and high phoretic mite rates (up to 52 mites per hundred bees). The establishment of DWV in colonies occurred after that of V. destructor and the mite infestation rate had a significant effect on the virus prevalence and load. CBPV appeared only transiently throughout the surveys. The data showed that, in tropical colonies with permanent brood rearing, V. destructor and DWV can reach high levels, but are still subject to seasonal variations that appear to be influenced by environmental conditions. This suggests that beekeeping practices could be adapted by favouring sites and periods for transhumance or acaricide treatment.

When European meets African honeybees (Apis mellifera L.) in the tropics: Morphological changes related to genetics in Mauritius Island (South-West Indian Ocean).

The previous genetic characterization of the honeybee population of Mauritius Island (Indian Ocean) revealed an ongoing process of hybridization between the first established African subspecies Apis mellifera unicolor and recently imported European subspecies (A. m. ligustica, A. m. carnica and A. m. mellifera). This context offers the rare opportunity to explore the influence of hybridization between African and European honeybees on phenotypic traits out of the case largely studied of the Africanized honeybee (hybrid between A. m. scutellata from South Africa and European subspecies). We thus conducted geometric morphometric analyses on forewings of 283 workers genetically characterized at 14 microsatellite loci to evaluate (1) if the morphological variability coincides well with the neutral genetic variability, (2) if hybrids exhibited rather parental, intermediate or transgressive traits, and (3) to test if fluctuating asymmetry (FA) of size and shape, as a measure of developmental stability, was elevated in hybrids (due to genetic stress) and/or European bees (due to unsuitable environment) compared to African bees. A strong concordance was found between morphological variability and neutral genetic variability, especially for wing shape, based on partial least-square analyses (PLS). However, on average, the morphology of hybrids was more similar to the African bees, potentially reflecting the dynamics and direction of introgression. Significant FA for wing size as well as wing shape was detected, suggesting the overall presence of stress during the development of the studied individuals. In contrast, the asymmetry levels do not differ according to the ancestry (African, European or hybrid) of the individuals. Therefore, if ongoing hybridization contributed to increasing the genetic and phenotypic diversity of the populations and influences its adaptive potential, developmental stressors could not be identified and their evolutionary consequences remain uncertain.

The complete mitochondrial genome of Apis mellifera unicolor (Insecta: Hymenoptera: Apidae), the Malagasy honey bee

The complete mitochondrial genome of the endemic Malagasy honey bee Apis mellifera unicolor is 16,373 bp and comprises 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes, and a control region. The mitochondrial genome closely resembles mitogenomes of other published Apis mellifera subspecies, and the phylogenetic analysis suggests that A. m. unicolor is distinct from other African (A) lineage honey bees but is most closely related to the honey bees from southern African: A. m. scutellata and A. m. capensis.

Pollen morphology of melliferous plants for Apis mellifera unicolor in the tropical rainforest of Ranomafana National Park, Madagascar

ABSTRACTThe morphological diversity of pollen brings important information on the taxonomy of plants present in past and current ecosystems. Regarding the rich biodiversity and the large number of endemic plant species on the island of Madagascar, pollen reference collections are still scarce for this part of the world. The main objective of this study was to conduct a preliminary investigation of pollen morphology of flowering plants visited by honeybees in a tropical rainforest of the south-east part of Madagascar during 2014 to 2015 (Ranomafana National Park – Fianarantsoa). Samples of 135 species belonging to 105 genera and 52 families were processed, employing the standard acetolysis method. Pollen reference slides of these melliferous plants were mounted. These pollen grains were then photographed and measured using light microscopy. The 135 collected species include 54 trees, 47 shrubs, 21 herbs, 12 lianas and one epiphyte, among which 85 taxa are endemic, 46 indigenous and four exotic. Pollen morphological characteristics of 106 species (85% endemic) are described here for the first time. Since these endemic plant taxa have co-evolved with the endemic honeybee of Madagascar, Apis mellifera unicolor, the implications of the pollen grain morphology for plant–pollinator co-evolution are discussed.

Genetic diversity and differentiation among insular honey bee populations in the southwest Indian Ocean likely reflect old geographical isolation and modern introductions.

With globalization the Western honey bee has become a nearly cosmopolitan species, but it was originally restricted to the Old World. This renowned model of biodiversity has diverged into five evolutionary lineages and several geographic “subspecies.” If Apis mellifera unicolor is indubitably an African subspecies endemic to Madagascar, its relationship with honey bees from three archipelagos in the southwest Indian Ocean (SWIO) hotspot of biodiversity is misunderstood. We compared recent mtDNA diversity data to an original characterization of the nuclear diversity from honey bees in the Mascarenes and Comoros archipelagos, using 14 microsatellites, but also additional mtDNA tRNALeu-cox2 analysis. Our sampling offers the most comprehensive dataset for the SWIO populations with a total of 3,270 colonies from 10 islands compared with 855 samples from Madagascar, 113 from Africa, and 138 from Europe. Comprehensive mitochondrial screening confirmed that honey bees from La Réunion, Mauritius, and Comoros archipelagos are mainly of African origin (88.1% out of 2,746 colonies) and that coexistence with European lineages occurs only in the Mascarenes. PCA, Bayesian, and genetic differentiation analysis showed that African colonies are not significantly distinct on each island, but have diversified among islands and archipelagos. FST levels progressively decreased in significance from European and African continental populations, to SWIO insular and continental populations, and finally among islands from the same archipelago. Among African populations, Madagascar shared a nuclear background with and was most closely related to SWIO island populations (except Rodrigues). Only Mauritius Island presented clear cytoplasmic disequilibrium and genetic structure characteristic of an admixed population undergoing hybridization, in this case, between A. m. unicolor and A. m. ligustica, A. m. carnica and A. m. mellifera-like individuals. Finally, global genetic clustering analysis helped to better depict the colonization and introduction pattern of honey bee populations in these archipelagos.

Autosomal and Mitochondrial Adaptation Following Admixture: A Case Study on the Honeybees of Reunion Island.

The honeybee population of the tropical Reunion Island is a genetic admixture of the Apis mellifera unicolor subspecies, originally described in Madagascar, and of European subspecies, mainly A. m. carnica and A. m. ligustica, regularly imported to the island since the late 19th century. We took advantage of this population to study genetic admixing of the tropical-adapted indigenous and temperate-adapted European genetic backgrounds. Whole genome sequencing of 30 workers and 6 males from Reunion, compared with samples from Europe, Madagascar, Mauritius, Rodrigues, and the Seychelles, revealed the Reunion honeybee population to be composed on an average of 53.2 ± 5.9% A. m. unicolor nuclear genomic background, the rest being mainly composed of A. m. carnica and to a lesser extent A. m. ligustica. In striking contrast to this, only 1 out of the 36 honeybees from Reunion had a mitochondrial genome of European origin, suggesting selection has favored the A. m. unicolor mitotype, which is possibly better adapted to the island’s bioclimate. Local ancestry was determined along the chromosomes for all Reunion samples, and a test for preferential selection for the A. m. unicolor or European background revealed 15 regions significantly associated with the A. m. unicolor lineage and 9 regions with the European lineage. Our results provide insights into the long-term consequences of introducing exotic specimen on the nuclear and mitochondrial genomes of locally adapted populations.

Genetic diversity of Varroa destructor parasitizing Apis mellifera unicolor in Madagascar

Varroadestructor is an invasive alien species that has been reported parasitizing the endemic honey bee of Madagascar, Apis mellifera unicolor, since 2010. Studying its nuclear genetic diversity and structure was our main goal. Using 11 microsatellite loci and 344 mites collected from 12 apiaries, we observed a low genetic diversity, with only 8 multilocus genotypes (MLG) identified. V. destructor populations form a single genetic cluster, clonal richness ranged from 0.02 to 0.20, and number of MLG within apiaries varied between one and six MLGs. About 69.5% of the mites analyzed harbored the same genotype (100%, homozygous), and 23.3% had a genotype differing by a single allele. The overall low diversity observed suggests one or multiple introductions of similar genotypes. The greater abundance of MLGs in High Land apiaries (eight MLGs) than on the east coast (two MLGs) and the presence of particular MLGs in High Land apiaries favor the hypothesis that V. destructor has been first introduced close to the international airport, and then spread to other regions by commercial exchanges.

Genetic diversity of the endemic honeybee: Apis mellifera unicolor (Hymenoptera: Apidae) in Madagascar

Apis mellifera unicolor is a tropical honeybee endemic of Madagascar. Comprehensive knowledge about its mitochondrial and nuclear genetic diversity and structuration was our main purpose. Samples of worker bees were collected from 867 colonies in 76 sites in Madagascar and 1 reference population in South Africa. PCR-restriction fragment length polymorphism (RFLP) and sequencing were used to reveal variability in the COI–COII mtDNA region. Seventeen microsatellite loci were used for studying the nuclear diversity. Three PCR-RFLP profiles were observed, among which 99.4 % belonged to A1 haplotype, 0.2 % to a new A haplotype, and 0.4 % to A4 haplotype. In microsatellite analysis, moderate genetic diversity values were found for Madagascar, together with low mean number of alleles ranging from 2.47 to 3.88 compared to South Africa. Bayesian clustering assignment methods and principal component analysis (PCA) separated populations into two genetic clusters which matched with geographic areas. Several hypotheses are discussed regarding to the low genetic diversity of A. m. unicolor in its native range.

Assessing hygienic behavior of Apis mellifera unicolor (Hymenoptera: Apidae), the endemic honey bee from Madagascar.

Hygienic behavior (HB) is one of the natural mechanisms of honey bee for limiting the spread of brood diseases and Varroa destructor parasitic mite. Objective of our study was to measure HB of Apis mellifera unicolor colonies (N = 403) from three geographic regions (one infested and two free of V. destructor) in Madagascar. The pin-killing method was used for evaluation of the HB. Responses were measured from 3 h 30 min to 7 h after perforation of the cells. Colonies were very effective in detecting perforated cells. In the first 4 h, on average, they detected at least 50% of the pin-killed brood. Six hours after cell perforation, colonies tested (N = 91) showed a wide range of uncapped (0 to 100%) and cleaned cells (0 to 82%). Global distribution of the rate of cleaned cells at 6 h was multimodal and hygienic responses could be split in three classes. Colonies from the three regions showed a significant difference in HB responses. Three hypotheses (geographic, genetic traits, presence of V. destructor) are further discussed to explain variability of HB responses among the regions. Levels of HB efficiency of A. mellifera unicolor colonies are among the greatest levels reported for A. mellifera subspecies. Presence of highly hygienic colonies is a great opportunity for future breeding program in selection for HB.

Spread and strain determination of Varroa destructor (Acari: Varroidae) in Madagascar since its first report in 2010

Varroa destructor is a major pest in world beekeeping. It was first detected in Madagascar in 2010 on the endemic honeybee Apis mellifera unicolor. To evaluate V. destructor spread dynamics in Madagascar a global survey was conducted in 2011-2012. A total of 695 colonies from 30 districts were inspected for the presence of mites. 2 years after its introduction, nine districts were found infested. Varroa destructor spread was relatively slow compared to other countries with a maximum progression of 40 km per year, the five newly infested districts being located next to the first infested ones. The incidence of mite infestation was also investigated by monitoring 73 colonies from five apiaries during 1 year (2011-2012). Sixty percent of local colony mortality was recorded after 1 year of survey. Varroa destructor strain determination was done by partial sequencing of the cytochrome oxidase I gene of 13 phoretic mites sampled in five districts. A single V. destructor mitochondrial haplotype was detected, the Korean type, also present in the closest African countries. A global pathogen survey was also conducted on the colonies inspected for mite presence. The greater wax moth, Galleria mellonella has been found in all colonies all over the country. Two other pathogens and morphological abnormalities in workers, such as deformed wings, were found associated with only V. destructor presence. A prevention management plan must be implemented to delimit mite spread across the island.