Prevalence of Nosema and Virus in Honey Bee (Apis mellifera L.) Colonies on Flowering Period of Acacia in Korea

Preliminary Survey of Pathogens in the Asian Honey Bee (Apis cerana) in Thailand

Widespread parasites, along with emerging threats, globalization, and climate change, have greatly affected honey bees' health, leading to colony losses worldwide. In this study, we investigated the detection of biotic stressors (i.e., viruses, microsporidian, bacteria, and fungi) in Apis cerana by surveying the colonies across different regions of Thailand (Chiang Mai in the north, Nong Khai and Khon Kaen in the northeast, and Chumphon and Surat Thani in the south, in addition to the Samui and Pha-ngan islands). In this study, we detected ABPV, BQCV, LSV, and Nosema ceranae in A. cerana samples through RT-PCR. ABPV was only detected from the samples of Chiang Mai, whereas we found BQCV only in those from Chumphon. LSV was detected only in the samples from the Samui and Pha-ngan islands, where historically no managed bees are known. Nosema ceranae was found in all of the regions except for Nong Khai and Khon Kaen in northeastern Thailand. Paenibacillus larvae and Ascosphaera apis were not detected in any of the A. cerana samples in this survey. The phylogenetic tree analysis of the pathogens provided insights into the pathogens' movements and their distribution ranges across different landscapes, indicating the flow of pathogens among the honey bees. Here, we describe the presence of emerging pathogens in the Asian honey bee as a valuable step in our understanding of these pathogens in terms of the decline in eastern honey bee populations.

Immune Response and Hemolymph Microbiota of Apis mellifera and Apis cerana After the Challenge With Recombinant Varroa Toxic Protein

The honey bee is a significant crop pollinator and key model insect for understanding social behavior, disease transmission, and development. The ectoparasitic Varroa destructor mite put threats on the honey bee industry. A Varroa toxic protein (VTP) from the saliva of Varroa mites contributes to the toxicity toward Apis cerana and the deformed wing virus elevation in Apis mellifera. However, the immune response and hemolymph microbiota of honey bee species after the injection of recombinant VTP has not yet been reported. In this study, both A. cerana and A. mellifera worker larvae were injected with the recombinant VTP. Then the expressions of the honey bee immune genes abaecin, defensin, and domeless at three time points were determined by qRT-PCR, and hemolymph microbial community were analyzed by culture-dependent method, after recombinant VTP injection. The mortality rates of A. cerana larvae were much higher than those of A. mellifera larvae after VTP challenge. VTP injection induced the upregulation of defensin gene expression in A. mellifera larvae, and higher levels of abaecin and domeless mRNAs response in A. cerana larvae, compared with the control (without any injection). Phosphate buffer saline (PBS) injection also upregulated the expression levels of abaecin, defensin, and domeless in A. mellifera and A. cerana larvae. Three bacterial species (Enterococcus faecalis, Staphylococcus cohnii, and Bacillus cereus) were isolated from the hemolymph of A. cerana larvae after VTP injection and at 48 h after PBS injections. Two bacterial species (Stenotrophomonas maltophilia and Staphylococcus aureus) were isolated from A. mellifera larvae after VTP challenge. No bacterial colonies were detected from the larval hemolymph of both honey bee species treated by injection only and the control. The result indicates that abaecin, defensin, and domeless genes and hemolymph microbiota respond to the VTP challenge. VTP injection might induce the dramatic growth of different bacterial species in the hemolymph of the injected larvae of A. mellifera and A. cerana, which provide cues for further studying the interactions among the honey bee, VTP, and hemolymph bacteria.

A Saliva Protein of Varroa Mites Contributes to the Toxicity toward Apis cerana and the DWV Elevation in A. mellifera

Varroa destructor mites express strong avoidance of the Apis cerana worker brood in the field. The molecular mechanism for this phenomenon remains unknown. We identified a Varroa toxic protein (VTP), which exhibited toxic activity toward A. cerana worker larvae, in the saliva of these mites, and expressed VTP in an Escherichia coli system. We further demonstrated that recombinant VTP killed A. cerana worker larvae and pupae in the absence of deformed-wing virus (DWV) but was not toxic to A. cerana worker adults and drones. The recombinant VTP was safe for A. mellifera individuals, but resulted in elevated DWV titers and the subsequent development of deformed-wing adults. RNAi-mediated suppression of vtp gene expression in the mites partially protected A. cerana larvae. We propose a modified mechanism for Varroa mite avoidance of worker brood, due to mutual destruction stress, including the worker larvae blocking Varroa mite reproduction and Varroa mites killing worker larvae by the saliva toxin. The discovery of VTP should provide a better understanding of Varroa pathogenesis, facilitate host-parasite mechanism research and allow the development of effective methods to control these harmful mites.

Analysis of the complete genome sequence of black queen cell virus JL1 from infected honeybees in China

There are six strains of the complete genomic sequences of black queen cell virus (BQCV) published in the GenBank, including South Africa (AF183905), South Korea (JX149531), Hungary 10 (EF517515), Poland 4 (EF517519), Poland 5 (EF517520) and Poland 6 (EF517521). Based on the six BQCV strains published in the GenBank, ten pairs of primers were designed in the present study using reverse transcription polymerase chain reaction to obtain the first complete genome sequence of a BQCV strain in China, called the BQCV China-JL1 strain (KP119603). A phylogenetic tree was then built to analyse their genetic relationships. The BQCV China-JL1 strain showed 86-93% similarity with the six strains published in the GenBank. The BQCV China-JL1 strain consisted of 8358 nucleotides (nt). The 5'-proximal open reading frame (ORF1) initiated at nt position 546 and terminated at nt position 4676, ORF3 initiated at nt position 4891 and terminated at nt position 5433, and the 3'-proximal ORF (ORF2) was located between nt positions 5750 and 8203.