Background: The health of honeybee colonies is critical for bee products and agricultural production, and colony health is closely associated with the bacteria in the guts of honeybees. Although colony loss in winter is now the primary restriction in beekeeping, the effects of different sugars as winter food on the health of honeybee colonies are not well understood. Therefore, in this study, the influence of different sugar diets on honeybee gut bacteria during overwintering was examined. Results: The bacterial communities in honeybee midguts and hindguts before winter and after bees were fed honey, sucrose, and high-fructose syrup as winter-food were determined by targeting the V3-V4 region of 16S rDNA using the Illumina MiSeq platform. The dominant microbiota in honeybee guts were the phyla Proteobacteria (63.17%), Firmicutes (17.61%; Lactobacillus, 15.91%), Actinobacteria (4.06%; Bifidobacterium, 3.34%), and Bacteroidetes (1.72%). The dominant taxa were conserved and not affected by season, type of overwintering sugar, or spatial position in the gut. However, the relative abundance of the dominant taxa was affected by those factors. In the midgut, microbial diversity of the sucrose group was higher than that of the honey and high-fructose syrup groups, but in the hindgut, microbial diversity of the honey and high-fructose groups was higher than that in the sucrose group. Sucrose increased the relative abundance of Actinobacteria (Bifidobacteriales Bifidobacteriaceae) and Alphaproteobacteria (Rhizobiales and Mitochondria) of honeybee midgut, and honey enriched the Bacteroidetes and Gammaproteobacteria (Pasteurellales) in honeybee hindgut. High-fructose syrup increased the relative abundance of Betaproteobacteria (Neisseriales: Neisseriaceae) of the midgut. Conclusion: The type of sugar used as winter food affected the relative abundance of the dominant bacterial communities in honeybee guts, not the taxa, which could affect the health and safety of honeybee colonies during overwintering. The presence of the supernal Alphaproteobacteria, Bifidobacteriales, and Lactobacillaceae in the gut of honeybees fed sucrose and cheaper than honey both indicate that sucrose is very suitable as the overwintering food for honeybees.

MicroRNAs (miRNAs), a class of non-coding small RNAs, are crucial regulatory factors in plants and animals at the post-transcriptional level. These tiny molecules suppress gene expression by complementary oligonucleotide binding to sites in the target messenger. Recently, the discovery of plant-derived miRNAs with cross-kingdom abilities to regulate gene expression in insects has promoted exciting discussion, although some controversies exist regarding the modulation of insect development by plant-derived miRNAs. Here, we review current knowledge about the mechanisms of miRNA biogenesis, the roles of miRNAs in coevolution between insects and plants, the regulation of insect development by plant-derived miRNAs, the cross-kingdom transport mechanisms of plant-derived miRNAs, and cross-kingdom regulation. In addition, the controversy regarding the modulation of insect development by plant-derived miRNAs also was discussed. Our review provides new insights for understanding complex plant–insect interactions and discovering new strategies for pest management and even crop genetic improvement.

Honeybees cannot synthesize arachidonic acid (ARA) themselves, only obtain it from food. Most pollen is deficient or contains a small amount of ARA. The necessity of supplementary ARA in bees’ diet has not been studied. The objective of this study was to investigate the effects of dietary ARA levels on the growth and immunity ofApis mellifera ligustica. A total of 25 honeybee colonies were randomly assigned to five dietary groups which were fed basic diets supplemented with 0, 2, 4, 6, and 8% of ARA. The diet with 4% ARA improved the body weight of newly emerged worker bees compared with the control group. Supplement of ARA in honeybee diets changed the fatty acid composition of honeybee body. SFA and MUFA contents of bees’ body declined, and PUFA content rised in the ARA group. Compared with the control group, the supplement of ARA in honeybee diets increased the contents of ARA, C22:6n-3 (DHA) and C18:3n-6 in bees’ body significantly, but decreased the contents of C16:1 and C18:3n-3. The diet supplied with 4% ARA reduced the mortality rate of honeybee infected withEscherichia coli. The activity of immune enzymes (phenoloxidase, antitrypsin, and lysozyme) and the mRNA expression levels of immune genes (defensin-2,toll,myd88, anddorsal) were improved by ARA diets to varying degrees depending on the ARA levels, especially 4% ARA. These results suggested that dietary ARA could improve the growth, survival, and immune functions of honeybees. Supplement of ARA in bees’ diet would be valuable for the fitness of honeybees.

Queen bees and worker bees both develop from fertilized eggs, whereas queens live longer than workers. The mechanism of this phenomenon is worth exploring. Antioxidant capacity, immune and IIS are the conserved mechanisms of aging. The importance of gut bacteria for health prompted us to connect with bee aging. Therefore, the differences of antioxidant, immune, IIS and gut microflora between queen and worker bees were compared to find potential mechanisms of queens’ longevity. The results showed queens had stronger antioxidant capacity and lower immune pathway and IIS activity than workers. The higher expression level of catalase and SOD1/2 in queens resulted in the stronger ROS scavenging ability, which leads to the lower ROS level and the reduced accumulation of oxidative damage products in queens. The lower IMD expression and higher antimicrobial peptides (AMPs) expressions in queens suggested that queens maintain lower immune pathway activity and stronger immune capacity than workers. Gut bacteria composition analysis indicated that queens had supernal Acetobacteraceae (notably Commensalibacter and Bombella), Lactobacillus and Bifidobacterium over workers. In conclusion, antioxidant, immune, IIS, and gut symbiotic bacteria all contribute to the longevity of queens. This study provides more insights into revealing the mechanisms of queens’ longevity.

This study was designed to determine the appropriate levels of tryptophan (trp) in the diet of Apis mellifera worker bees. Newly emerged worker bees were enclosed in wooden cages in an incubator at 32°C with 55–60% humidity and fed a diet including 9, 10, 11, 12, 13, and 14 mg/g trp for 12 days. When the trp level was 11 mg/g, worker bees demonstrated better performance in terms of food intake, body weight, and total protein accumulation. However, 12 mg/g dietary trp promoted trp deposition in the worker bees, stimulated hypopharyngeal gland development, enhanced the survival rate and expedited the formation of 5-HT (5-hydroxytryptamine). The worker bees fed with 13 and 14 mg/g trp had higher malondialdehyde (MDA) levels, which suggested that a higher level of trp may be disadvantageous in maintaining worker-bee antioxidant ability, because MDA was the end product of lipid peroxidation. We also found that dietary trp regulated the mRNA expression of 5-HTRs and tryptophan hydroxylase (TPH) in a dose-dependent manner, which was related to phototaxis, aggression, and other factors. In conclusion, dietary trp exerts regulatory roles in the growth, development and some physiological and biochemical properties of worker bees. Therefore, 11–12 mg/g tryptophan is optimal for A. mellifera adult worker bees.