Invasive populations often experience founder effects: a loss of genetic diversity relative to the source population, due to a small number of founders. Even where these founder effects do not impact colonization success, theory predicts they might affect the rate at which invasive populations expand. This is because secondary founder effects are generated at advancing population edges, further reducing local genetic diversity and elevating genetic load. We show that in an expanding invasive population of the Asian honey bee (Apis cerana), genetic diversity is indeed lowest at range edges, including at the complementary sex determiner, csd, a locus that is homozygous-lethal. Consistent with lower local csd diversity, range edge colonies had lower brood viability than colonies in the range centre. Further, simulations of a newly-founded and expanding honey bee population corroborate the spatial patterns in mean colony fitness observed in our empirical data and show that such genetic load at range edges will slow the rate of population expansion.

The interactions between plants and pollinators are complex. Flower volatiles as special olfactory cues could influence the foraging choices of pollinators. Here, we conducted bioassays to evaluate the role of flower volatiles on the attraction of honey bees (native Apis cerana and exotic Apis mellifera) to pears (native Pyrus bretschneideri and exotic Pyrus communis). Chemical and electrophysiological approaches were used to determine flower volatiles and evaluate the antennal responses of honey bees to volatiles from pear flowers. Bioassays demonstrated that flower volatiles were crucial for the attraction of honey bees to pear flowers; honey bees preferred to forage on P. communis flowers (p > 0.05), with approximately 64.37 ± 0.02% (A. mellifera) and 62.10 ± 0.02% (A. cerana) foraging on P. communis. Flowers of P. communis and P. bretschneideri yielded 27 and 31 compounds, respectively, with 17 of them being common. Honey bee antennae responded to 16 chemicals, including 5 contained in both pear species: 1-nonanol, linalool, methyl 2-hydroxy-3-methylpentanoate, methyl L-isoleucinate, and α-farnesene. In addition, there were 8 electrophysiologically active compounds in P. bretschneideri: methyl L-valine ester, benzaldehyde, 6-methyl-5-hepten-2-one, isophorone, 2-methyl octane, longicyclene, longifolene, and caryophyllene; and 3 electrophysiologically active compounds in P. communis: β-ocimene, 4-oxoisophorone and lilac alcohol D. In conclusion, our study demonstrated the significant impact of pear flower volatiles on honey bee foraging choices. This knowledge provides a basis for the selection of honey bees for pear pollination and lays a foundation for further study of the chemical communication of pear attractiveness to honey bees.

Pollen is essential to the development of honey bees. The nutrients in bee pollen vary greatly among plant species. Here, we analyzed the differences in the amino acid compositions of pear (Pyrus bretschneideri), rape (Brassica napus), and apricot (Armeniaca sibirica) pollens and investigated the variation in hemolymph metabolites and metabolic pathways through untargeted metabolomics in caged adult bees at days 7 and 14. The results showed that the levels of five essential amino acids (isoleucine, phenylalanine, lysine, methionine, and histidine) were the highest in pear pollen, and the levels of four amino acids (isoleucine: 50.75 ± 1.93 mg/kg, phenylalanine: 87.25 ± 2.66 mg/kg, methionine: 16.00 ± 0.71 mg/kg and histidine: 647.50 ± 24.80 mg/kg) were significantly higher in pear pollen than in the other two kinds of bee pollen (p < 0.05). The number of metabolites in bee hemolymph on day 14 (615) was significantly lower than that on day 7 (1466). The key metabolic pathways of bees, namely, “sphingolipid metabolism (p = 0.0091)”, “tryptophan metabolism (p = 0.0245)”, and “cysteine and methionine metabolism (p = 0.0277)”, were significantly affected on day 7. There was no meaningful pathway enrichment on day 14. In conclusion, pear pollen had higher nutritional value among the three bee pollens in terms of amino acid level, followed by rape and apricot pollen, and the difference in amino acid composition among bee pollens was reflected in the lipid and amino acid metabolism pathways of early adult honey bee hemolymph. This study provides new insights into the physiological and metabolic functions of different bee pollens in bees.

With the availability of various plants in bloom simultaneously, honey bees prefer to collect some pollen types over others. To better understand pollen’s role as a reward for workers, we compared the digestibility and nutritional value of two pollen diets, namely, pear (Pyrus bretschneideri Rehd.) and apricot (Armeniaca sibirica L.). We investigated the visits, pollen consumption, and pollen extraction efficiency of caged Apis mellifera workers. Newly emerged workers were reared, and the effects of two pollen diets on their physiological status (the development of hypopharyngeal glands and ovaries) were compared. The choice-test experiments indicated a significant preference of A. mellifera workers for apricot pollen diets over pear pollen diets (number of bees landing, 29.5 ± 8.11 and 9.25 ± 5.10, p < 0.001 and pollen consumption, 0.052 ± 0.026 g/day and 0.033 ± 0.013 g/day, p < 0.05). Both pollen diets had comparable extraction efficiencies (67.63% for pear pollen and 67.73% for apricot pollen). Caged workers fed different pollen diets also exhibited similar ovarian development (p > 0.05). However, workers fed apricot pollen had significantly larger hypopharyngeal glands than those fed pear pollen (p < 0.001). Our results indicated that the benefits conferred to honey bees by different pollen diets may influence their foraging preference.