CrynodebConifers are widely planted for timber production as they can grow rapidly even under difficult conditions, have good yields, and produce suitable wood for industrial use. Bark-feeding and woodboring insect pests can have significant negative impacts on coniferous forests and wood production by killing trees, damaging the wood, or vectoring other pests such as nematodes, bacteria, or fungi. In the United Kingdom (UK), little is known about these pests, however, the damage they cause is expected to increase in the future due to climate change and the growth of international trade. This thesis aimed to develop a better understanding of the ecology of wood-boring and bark-feeding insects in coniferous tree forestry in the UK by applying genetic approaches. Firstly, communities of bark-feeding and wood-boring beetles were studied. DNA-barcoding was evaluated and revealed to be an accurate method to identify many wood-boring and bark-feeding beetles in the UK (Chapter 2). Beetle communities associated with three conifer species (Sitka spruce, Noble fir, and Scots pine) in Wales were then assessed using DNA barcoding (Chapter 3). Within a nested sampling design, larvae collected from several wood-decay successional stages in standing trap trees and log piles were identified. The results provided insight into successional patterns of community composition for each conifer species and the environmental variables driving the observed differences. The data also provided informative material for monitoring and management of novel pest species, and for conservation and promotion of beneficial species. Unexpectedly, two Kyklioacalles roborislarvae were identified from underneath the bark of a Noble fir log (Chapter 6). This revealed an unexpected habitat for this rare flightless weevil and highlighted that the ecology of this species is not well understood.
Moving from communities, genetic variation was studied at the species level for the native pest Tomicus piniperda (Chapter 4) and the invasive pest Ips typographus (Chapter 5). Genetic diversity within and between populations was assessed using various combinations of mitochondrial DNA sequencing, nuclear microsatellites, and Restriction-site Associated DNA sequencing (RAD-Seq) of Single nucleotide polymorphism (SNPs). Phylogeography analyses of T. piniperda confirmed the complexity of its postglacial history and linked the UK individuals to a genetic group widely distributed throughout Europe while excluding more recent coancestry with 3 other groups previously identified. Scottish samples exhibited elevated levels of genetic variation suggesting colonisation from a northern refugial area. High levels of genetic differentiation between UK populations suggested limited dispersal between forest stands despite the good dispersal abilities of the beetle. Finally, the origin and demography of I. typographus populations found in Kent (2018, 2019, and 2020) and in Felixstowe port (England) were examined. Results confirmed that the first outbreak of I. typographus was comprised of a sufficient number of colonising individuals to mean that the invasive population retained levels of variation equivalent to those of established populations in Europe. Samples from 2019 and 2020 and Felixstowe samples all displayed genetic signatures consistent with an origin from the South-West (S-W) Europe. On the other hand, the Kent 2018 population were unlikely to have originated from the North-East of Europe but displayed genetic characteristics that were not
consistent with the genetic characteristics of the S-W Europe (microsatellite and SNPs data). The first outbreak of Ips typographus in the UK may have originated from regions not sampled in this study and/or from multiple sources. For both pest species studied, the English Channel does not seem to act as a barrier to dispersal between Europe and the UK. Overall, the results of this thesis informed the ecology of wood-boring and bark-feeding pest species in the UK. They also provide genetic resources that can be operationalised and may help reduce the damage to the UK forestry sector by improving monitoring, surveillance, management, and control of these pests.
|Goruchwyliwr||Paul Shaw (Goruchwylydd), Niall McKeown (Goruchwylydd) & Peter Dennis (Goruchwylydd)|