Invasive species such as Bombus terrestris represent a severe threat that can result in the decline of local biodiversity. We examined the habitat suitability for B. terrestris invasion in East Asian countries and the risk of habitat overlap with 24 bumblebee species from different groups in China. All East Asian countries were predicted to be susceptible to invasion by B. terrestris, with the highest habitat suitability occurring in China followed by Japan, North Korea, South Korea and Mongolia. Within China, which is a global biodiversity hotspot for bumblebees, three different regions, north-west, central to south-east and north-east, were predicted as being highly suitable for invasion. In China, the group of species closely related to B. terrestris showed higher sensitivity (89%) to habitat overlap with B. terrestris than did the group of non-closely related species (73%). The risk of overlap for the three major regional bumblebees within China decreased in the order southern region, northern region and Tibetan Plateau region. Due to the sensitivity of habitat suitability and overlap, the use of the introduced European bumblebee B. terrestris for pollination services should be discouraged in regions with overlapping habitats in China, and management strategies should be implemented to conserve the vulnerable bumblebees in all East Asian countries.

Pear (Pyrus bretschneideri) is characterized by being self-incompatible and dependent on cross-pollination to set fruit. Honeybee (Apis mellifera) is considered the most important pollinator of pear. Nevertheless, limited pollen transfer has been cited as the main cause of poor fruit set in many pear orchards. Here, we tested the following hypotheses: (i) colony manipulations increase the pollen collection tendency of honeybees and (ii) the proportion of pollen loads being returned to the hive is from the target plant. The technique reliably and rapidly estimates the pollination of honeybees tested under different colony manipulations: (1) using pollen trapping (PT); (2) PT with sugar syrup feeding (SS) (PTSS); (3) SS alone and (4) control without PT and SS. The results clearly show that the pollen collection of honeybees during the experiment was significantly affected (P < 0.05) by colony manipulations. The mean amount of pollen harvested daily was higher for PTSS (19.4 g) and PT (16.4 g) than for SS (12.85 g) and control (8.7 g) colonies. Therefore, PTSS was the most effective treatment for increasing pear pollen collection; other treatments such as PT and SS could also be useful. This study was important for determining how the behavior of honeybee colonies is shaped through colony manipulation to enhance pollen collection of less preferred pear flowers, which is critical when pollination is required.

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.

The vitellogenin receptor (VgR) belongs to the low-density lipoprotein receptor (LDLR) family, responsible for mediating the endocytosis of vitellogenin (Vg) into the ovaries to promote ovarian growth and oviposition. Here, we cloned and measured VgR gene expression characteristics in the bumblebee Bombus lantschouensis. RNA interference was used to validate VgR function. The results showed that the full length of the BLVgR cDNA was 5519 bp, which included a 5280 bp open reading frame encoding 1759 amino acids (AAs). Sequence alignment revealed that the protein contained 12 LDLa, 5 EGF, 2 EGF-CA and 10 LY domains. Phylogenetic analysis showed that BLVgR and the VgR of Bombus terrestris clustered together and the tree of bumblebees (Bombus) appeared as one clade next to honeybees (Apis). Transcript expression analysis showed that BLVgR was expressed in all tested tissues and showed the highest abundance in the ovaries. BLVgR expression was present in all developmental stages. However, the expression level in larvae was extremely low. In addition, the expression of BLVgR was significantly upregulated after egg laying in both workers and queens. In new emerging workers injected with 5 µg of VgR dsRNA, the expression level of BLVgR was 4-fold lower than that in the GFP dsRNA-injected group after 72 h. Furthermore, BLVgR silencing significantly reduced the number of eggs laid (3.67 ± 1.96 eggs) and delayed the first egg-laying time (16.31 ± 2.07 days) in worker microcolonies when compared to dsGFP (37.31 ± 4.09 eggs, 8.15 ± 0.22 days) and DEPC-treated water injected controls (16.42 ± 2.24 eggs, 10.00 ± 0.37 days). In conclusion, the BLVgR gene and its reproductive function were explored in the bumblebee B. lantschouensis. This gene plays an important role in egg laying time and egg number.