Interaction between Thiamethoxam and Deformed Wing Virus Type A on Wing Characteristics and Expression of Immune and Apoptosis Genes in Apis mellifera.

Honey bees are economically important insects for crop pollination. They play a significant role as pollinators of wild plants and agricultural crops and produce economical products, such as honey, royal jelly, wax, pollen, propolis, and venom. Despite their ecological and economical importance, the global honey bee population is in decline due to factors including pathogens, parasites, intensive agriculture, and pesticides. Moreover, these factors may be interlinked and exacerbate the loss of honey bees. This study aimed to investigate the interaction between a pesticide, thiamethoxam, and deformed wing virus type A (DWV-A) to honey bees and the effects on survival rate, wing characteristics, and expression of immune and apoptosis genes in Apis mellifera. We described the potential interaction between thiamethoxam and DWV-A on honey bee wing characteristics, DWV-A loads, and the expressions of immune (defensin, abaecin, and hymenoptaecin) and apoptosis genes (buffy, apaf1, caspase3-like, caspase8-like, and caspase9-like). Honey bee larvae were fed with three different thiamethoxam doses (0.001, 1.4, and 14.3 ng/µL of the diet). Then, thiamethoxam-treated white-eyed pupae were injected with 107 copy numbers/honey bee of the DWV-A genome. The interaction between thiamethoxam and DWV-A caused a high mortality rate, crippled wings in newly emerged adult honey bees (100%), and resulted in induced expression of hymenoptaecin gene compared to the control group, while downregulation of caspase8-like, caspase9-like genes compared to the DWV injection group. Therefore, the potential interaction between thiamethoxam and DWV-A might have a deleterious effect on honey bee lifespan. The results from this study could be used as a tool to combat DWV-A infection and mitigate pesticide usage to alleviate the decrease in the honey bee population.

Comparative Study of Antimicrobial Properties of Bee Venom Extracts and Melittins of Honey Bees.

Bee venom (BV), or apitoxin, is a complex substance produced by a gland in the abdominal cavity of bees. The main component of BV is melittin, which is a largely studied substance due to its biological properties. To date, the most well-known bee venom and melittin are derived from domesticated honey bees, while venom and melittin derived from wild honey bees have been under-investigated. Hence, this study primarily reports the antimicrobial activities of bee venom and synthetic melittin derived from four different honey bee species (Apis mellifera, A. cerana, A. dorsata, and A. florea) in Thailand. All the bee venom extracts and melittins showed more robust antibacterial activities against Gram-positive (Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, S. aureus MRSA, and S. epidermidis) than Gram-negative bacteria (Escherichia coli, Klebsiella pneuminiae, and Salmonella typhimurium) or a fungus (Candida albicans), while the synthetic melittins also have antimicrobial activity at higher concentrations than the bee venom extract. Furthermore, the A. cerana venom extract showed the highest activity against the tested bacteria, followed by A. mellifera, A. florea, and A. dorsata. Therefore, A. cerana venom may be further developed for use in medical applications as a potential alternative agent against Gram-positive bacteria and antibiotic-resistant bacteria.

Effects of Deformed Wing Virus Infection on Expressions of Immune- and Apoptosis-Related Genes in Western Honeybees (Apis mellifera).

Honeybees are globally threatened by several pathogens, especially deformed wing virus (DWV), as the presence of DWV in western honeybees is indicative of colony loss. The high mortality rate is further exacerbated by the lack of effective treatment, and therefore understanding the immune and apoptosis responses could pave an avenue for the treatment method. In this study, DWV was directly injected into the white-eyed pupae stage of western honeybees (Apis mellifera). The DWV loads and selected gene responses were monitored using the real-time PCR technique. The results showed that honeybee pupae that were injected with the highest concentration of viral loads showed a significantly higher mortality rate than the control groups. Deformed wings could be observed in newly emerged adult bees when the infected bees harbored high levels of viral loads. However, the numbers of viral loads in both normal and crippled wing groups were not significantly different. DWV-injected honeybee pupae with 104 and 107 copy numbers per bee groups showed similar viral loads after 48 h until newly emerged adult bees. Levels of gene expression including immune genes (defensin, abaecin, and hymenoptaecin) and apoptosis genes (buffy, p53, Apaf1, caspase3-like, caspase8-like, and caspase9-like) were analyzed after DWV infection. The expressions of immune and apoptosis genes were significantly different in infected bees compared to those of the control groups. In the pupae stage, the immune genes were activated by injecting DWV (defensin and hymenoptaecin) or Escherichia coli (defensin, abaecin, and hymenoptaecin), a positive control. On the contrary, the expression of apoptosis-related genes (buffy, caspase3-like, caspase8-like, and caspase9-like genes) was suppressed at 96 h post-infection. In DWV-infected newly emerged adult bees, abaecin, hymenoptaecin, Apaf1, and caspase8-like genes were upregulated. However, these genes were not significantly different between the normal and crippled wing bees. Our results suggested that DWV could activate the humoral immunity in honeybees and that honeybee hosts may be able to protect themselves from the virus infection through immune responses. Apoptosis gene expressions were upregulated in newly emerged adult bees by the virus, however, they were downregulated during the initial phase of viral infection.

Comparative susceptibility and immune responses of Asian and European honey bees to the American foulbrood pathogen, Paenibacillus larvae.

American foulbrood (AFB) disease is caused by Paenibacillus larvae. Currently, this pathogen is widespread in the European honey bee-Apis mellifera. However, little is known about infectivity and pathogenicity of P. larvae in the Asiatic cavity-nesting honey bees, Apis cerana. Moreover, comparative knowledge of P. larvae infectivity and pathogenicity between both honey bee species is scarce. In this study, we examined susceptibility, larval mortality, survival rate and expression of genes encoding antimicrobial peptides (AMPs) including defensin, apidaecin, abaecin, and hymenoptaecin in A. mellifera and A. cerana when infected with P. larvae. Our results showed similar effects of P. larvae on the survival rate and patterns of AMP gene expression in both honey bee species when bee larvae are infected with spores at the median lethal concentration (LC50 ) for A. mellifera. All AMPs of infected bee larvae showed significant upregulation compared with noninfected bee larvae in both honey bee species. However, larvae of A. cerana were more susceptible than A. mellifera when the same larval ages and spore concentration of P. larvae were used. It also appears that A. cerana showed higher levels of AMP expression than A. mellifera. This research provides the first evidence of survival rate, LC50 and immune response profiles of Asian honey bees, A. cerana, when infected by P. larvae in comparison with the European honey bee, A. mellifera.

Capsid Gene Divergence of Black Queen Cell Virus Isolates in Thailand and Japan Honey Bee Species.

Black queen cell virus (BQCV) has been found in honey bees worldwide. By using the reverse transcription polymerase chain reaction (RT-PCR) technique, BQCV was detected in a non-native species, Apis mellifera L., collected in both Thailand and Japan, and three other honey bee species (Apis cerana indica F., Apis dorsata F., and Apis florae F.) native to Thailand and Apis cerana japonica F. native to Japan. Based on the capsid coding region, the phylogenetic analysis showed that the BQCV strains found in A. cerana indica and A. cerana japonica were similar within the group and closer to BQCV in Asia. It is interesting to note that the genetic variation of the BQCV isolates was more associated with geographic origin than the host bee species from which the isolates were obtained.