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Title: Comparative susceptibility and immune responses of Asian and European honey bees to the American foulbrood pathogen

item KRONGDANG, SASIPRAPA - Chiang Mai University
item Evans, Jay
item Chen, Yanping - Judy
item CHANTAWANNAKUL, PANUWAN - Chiang Mai University

Submitted to: Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2018
Publication Date: 3/26/2018
Citation: Krongdang, S., Evans, J.D., Chen, Y., Chantawannakul, P. 2018. Comparative susceptibility and immune responses of Asian and European honey bees to the American foulbrood pathogen. Insect Science. 00:1-12.

Interpretive Summary: One of the most destructive diseases affecting health of honeybee larvae is American foulbrood disease caused by a bacterium called Paenibacillus larvae. However, little is known about the impacts of this bacterium on the Asian honey bee, a close cousin of the European honey bee, as well as the differences in immune responses of two bee hosts. We conducted a study to investigate bacterial infection in two bee species. Our results showed that larvae of Asian honey bees were more susceptible to this bacterium and died more rapidly after infection, compared to larvae of European honey bees. In addition, Asian honey bees were found to mount higher immune responses than European honey bees in response to bacterial infection. The results illustrate that host genetic variation could play a critical role in the progress and outcome of bacterial disease infection in honey bees and deepen our understanding of the complex interactions of bacterial pathogen and host defenses. The results from our study should be of interest to the researchers, graduate students, regulators, and beekeepers worldwide.

Technical Abstract: 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 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 AMPs gene expressions in both honey bee species, when bee larvae are infected spores at the median lethal concentration (LC50) for A. mellifera. All AMPs of infected bee larvae showed significant up-regulation compared with non-infected 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 AMPs 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.