American foulbrood and its causative agent, Paenibacillus larvae, in New Zealand’s registered hives and apiaries

摘要

Though the honey bee (Apis mellifera) is exposed to an extensive diversity of parasites and pathogens from multiple kingdoms, few are as devastating as American foulbrood. American foulbrood is a highly contagious bacterial disease, of which the causative agent (bacterium Paenibacillus larvae) infects honey bee brood through the ingestion of its spores, ultimately leading to the death of the infected larva and the collapse of the infected hive. Paenibacillus larvae’s genotypes (ERIC I-IV) exhibit differing ‘killing time’ of infected larvae, resulting in different larval and colony level virulence of the disease within hives.American foulbrood is found in New Zealand’s registered hives, and poses a threat to the country’s apiculture industry. The first objective of this thesis was to perform a genetic analysis on New Zealand’s P. larvae field strains using the well-established methodology of rep-PCR with MBO REP1 primers. A total of 172 bacteria isolates were gathered from registered hives from 2011 to 2014 and examined. The MBO REP1 primer identifies the ‘beta’ genetic subgroups of P. larvae. By identifying beta subgroups, the ERIC genotypes that are present in New Zealand can also be concluded. The genetic analysis of P. larvae using rep-PCR is a first for New Zealand, and appears to be a first for Australasia. The second objective of this thesis was to conduct a temporal and geographical statistical analysis on American foulbrood infection rate trends in New Zealand’s national and regional, divided into seven regions, registered hives and apiaries from 1994 to 2013.The genetic analysis of P. larvae detected three ‘beta’ genotypic subgroups: B, b, and Б. From these findings it was concluded that ERIC I and ERIC II are present in New Zealand. Previous to my findings, subgroup B and Б and ERIC II genotype had not been recorded outside of Europe. The statistical analysis reported that American foulbrood infection rates were significantly decreasing nationally. Results also reported that four of the seven regions’ infection rates were significantly decreasing, whilst three regions were significantly increasing.Conclusions on the subgroups and genotypes present in New Zealand gives the first insight to the virulence and occurrence of P. larvae strains. Additionally, the use of rep-PCR for the genetic analysis of P. larvae enables this thesis to contribute to the increasing knowledge on American foulbrood. By examining the temporal and geographic dynamics of American foulbrood, the results allow for the evaluation of current management strategies and the most recent understanding on the national and regional infection rates of the disease.