Climate change and global trade are driving rising threats to British forests from insect pests, with impacts ranging from reduced timber yields to losses in biodiversity and carbon storage. Drawing on a comprehensive assessment of 56 pest species, this presentation highlights the origins, impacts, and management of both native and non-native pests, identifies tree genera most at risk, and examines the role of trade, climate, and management in shaping outcomes. This talk will highlight several high-impact pests, including large pine weevil and bark beetles and advocate for a systems-level Integrated Pest Management (IPM) approach to strengthen forest resilience and anticipate future threats.
Q&A with Katy Dainton
Katy Dainton is a Research Entomologist at Forest Research where she develops Integrated Pest Management (IPM) tools and strategies for forest pests. This includes designing monitoring techniques, advancing non-chemical controls, managing the Rhizophagus grandis breeding programme, and providing specialist advice on tree health in northern Britain. She joined Forest Research in 2015 after completing an MSc in IPM, following earlier work with Natural England and a career in the arts and heritage sector.
How can we tell when a new pest species has been introduced? Presumably some new species are ‘naturally’ colonising under climate change.
Sometimes it is obvious when something has been introduced, for example there are several pest species that have established near sites handling imported timber or plant material. Conversely, there are also some pests for which current consensus holds that the species arrived in Britain ‘of its own accord’ (i.e. naturally dispersed here). This ‘natural’ dispersal may of course have only been facilitated by anthropogenic climate change, though. There is also evidence that some species arrive via both routes. For others, it is hard to be sure exactly how they got here. This is because some forest pest species live cryptic lifestyles and exist (for some time after arrival, at least) as small populations. This means they are not always immediately detected upon their arrival, and thus we cannot be sure if the place we first detect the species is truly the site of its first arrival. Sometimes it is possible to track backwards and pinpoint a clear first site of establishment, but not always.
What are the worst forest pests in mainland Europe which aren’t yet a problem in the UK?
The obvious answer would be Ips typographus, the Eight-toothed Spruce Bark Beetle. Populations of this species have been recorded in south and east England since 2018, initiating a programme of surveillance and eradication that have, so far, prevented the beetle from becoming established in the UK. In mainland Europe, though, this beetle is the primary pest of concern in the context of forestry. It has killed millions of spruce trees and had devastating landscape-wide impacts. And whilst it’s not killing trees in Britain yet, there are fears that climate change may facilitate it to become a problem in the future. So far we’re fortunate in that all the arrivals have been in southeast England, where there is a limited amount of spruce planted and eradication efforts are relatively feasible. If the beetle was to turn up in the more substantial forestry plantations of northern and western Britain, that’s when the real problems would begin.
Two other pests on our radar are Pine Processionary moth (Thaumetopoea pityocampa) and Pine Wood Nematode (Bursaphelenchus xylophilus), which is vectored by Monochamus longhorn beetles. Pine processionary moth has much the same impacts as Oak Processionary moth (Thaumetopoea processionea) (i.e. urticating hairs), but feeds on pines instead of oaks. This species has spread to northern France fairly recently and may well arrive in Britain soon.
Is the Large Pine Weevil only considered a pest in artificial pine plantations, or in native coniferous forest too?
Hylobius abietis, the Large Pine Weevil, has been considered a forest pest in the UK for as long as we have been clear felling and restocking forests. That is to say that its status as a pest is entirely linked to human management of forests. It could be considered a ‘man-made’ pest. The reason for this is because it relies on conifer stumps to breed. In a natural situation, stumps are a relatively scarce resource in the landscape. On a clear fell site, in contrast, there is a huge abundance of stumps, and consequently we see a huge abundance of Large Pine Weevils. When adults weevils emerge on clear fells sites they feed on newly planted saplings, sometimes decimating up to 100% of each year’s new crop. Although they only breed in conifer stumps, they will feed on pretty much any tree species. This phenomenon is, again, driven by the nature of clear felling practices. In a natural woodland, the weevils would feed on a variety of different trees growing at different stages. In clear fells, all trees are at the same stage of development at a given time, which makes the newly planted saplings the only food source and therefore very vulnerable. Without any control measures, these get merrily demolished by the weevils.
Are there any ‘nature-friendly’ control methods for Large Pine Weevils being trialled in Britain? E.g. nematodes or sapling stem coatings?
Yes to both of those things! To explain the first option, there’s a native nematode species which can be released as a ‘drench’ and applied to conifer stumps. The nematodes hunt down the Large Pine Weevil larvae and pupae and kill them, thereby reducing the proportion of the weevil population which makes it to adulthood. This methodology for control has been used extensively in Wales, but there are logistical barriers to greater uptake. The method requires a substantial volume of water and a lot of heavy machinery. Transporting these across rugged forestry landscapes is challenging. The second approach – ‘sapling stem coatings’ – is used extensively in Scandinavia as a tree protection method. This methodology involves coating the stems of young saplings in a protective wax to deter and prevent herbivory from weevils. Unfortunately, whilst the approach seems to work in Scandinavia, it doesn’t work so well in the UK. We think this is because our Large Pine Weevil populations are just so large – the collective power of many nibbles from many weevils are enough to overcome the protective layer!
With a bit more research there’s hope that one of these more ‘nature-friendly’ control methods could become operationally viable in the British context. But sadly for now neither is feasible nor cost effective enough for widespread uptake.
Presumably the more diverse a forest is, the more resilient it is to damage from pests? Is the ultimate problem monocultures?
A complex question! On the face of it, yes, greater tree diversity does seem to confer greater resilience to pests and we do see specific examples of reduced pest damage in mixtures compared to monocultures. In terms of long-term resilience to known and unknown pests as well as increasingly extreme climate conditions, diversifying tree species seems a sensible option so that even if some of the crop is lost to pests and diseases, not all of the trees are. However, there are logistical advantages to monocultures that make them easier to manage. Different trees grow at different rates and in different ways, and so managing a forest for production when you have a mix of trees is more complicated. The more complex the tree species mix is the more ‘management-needy’ the forest is, and this can be expensive. More complex management also brings greater risk of mechanical damage to trees. Another reason most trees are grown in monocultures is because many tree planting sites are actually only suitable to growing a small number of different types of trees (e.g. because of high winds, poor soil quality, boggy ground, cold temperatures, etc.). From a tree health perspective, the most important requisite for reducing the risk of pest damage is ensuring your trees are generally healthy. There’s also some interesting research that has recently come out showing that as tree diversity increases the number of potential insect forest pests also increases. This is logical because with more tree diversity you would also expect more insect diversity in general. All that is to say that although we would recommend diversifying tree species and planting mixed-species plantations, we appreciate this is not always straightforward to do in practice! The key thing is to ensure that the trees are suitable for the site they are planted on and are therefore growing happily as that is the best way to reduce susceptibility to pests and diseases.
Literature References
The key reference, upon which this entoLIVE talk is based, is:
- Dainton et al. (2026) ‘Forest pests in 21st century Britain: A review of impacts and management’: https://academic.oup.com/forestry/article/99/4/cpag061/8793149
Other useful references:
- Barzman et al. (2015) ‘Eight principles of integrated pest management’: https://link.springer.com/content/pdf/10.1007/s13593-015-0327-9.pdf
- Evans (1997) ‘The present position of forest entomology in Great Britain’: https://academic.oup.com/forestry/article-abstract/70/4/327/592938
- Freer-Smith and Webber (2017) ‘Tree pests and diseases: the threat to biodiversity and the delivery of ecosystem services’: https://link.springer.com/content/pdf/10.1007/s10531-015-1019-0.pdf
- Munro (1927) ‘The present position of forest entomology in Great Britain’: https://www.cabidigitallibrary.org/doi/full/10.5555/19270501436
- Sing et al. (2017) ‘A review of the effects of forest management intensity on ecosystem services for northern European temperate forests with a focus on the UK’: https://academic.oup.com/forestry/article-abstract/91/2/151/4282674
Further Info
- Defra UK Plant Health Risk Register 2025: https://planthealthportal.defra.gov.uk/pests-and-diseases/uk-plant-health-risk-register/index.cfm
- UK Government Plant Biosecurity Strategy for Great Britain 2023 to 2028: https://www.gov.uk/government/publications/plant-biosecurity-strategy-for-great-britain-2023-to-2028/plant-biosecurity-strategy-for-great-britain-2023-to-2028
- Forest Research’s UK Forestry Standard: https://assets.publishing.service.gov.uk/media/651670336a423b0014f4c5c0/Revised_UK_Forestry_Standard_-_effective_October_2024.pdf
- Review of the Forest Trapping Network Year One Rollout 2022: https://cdn.forestresearch.gov.uk/2024/01/FTN-2022-full-report_final_acc.pdf
- Observatree Explained: A layperson’s Report: https://www.observatree.org.uk/media/1241/final-laymans-report.pdf
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