Christmas trees threatened by increase in pine weevil population

Britain's Christmas tree industry is under pressure from a tiny insect that could severely damage young trees following restrictions on certain insecticides. The large pine weevil, barely the size of a fingernail, gnaws through the delicate bark of Sitka spruce to feed on its sap, leaving the tree vulnerable to environmental stress. While mature trees can often withstand this damage, younger saplings are at serious risk, and bark loss can be fatal.

Each year, approximately 35 million young Sitka spruce trees are planted in the UK, making it the country's third largest crop after wheat and barley, and accounting for around half of the 2 billion forestry market. A notable example is the 40-foot Sitka spruce from Kielder Forest in Northumberland, which is displayed annually outside the Houses of Parliament at the base of Big Bens Elizabeth Tower.

Without effective pest control, pine weevils can devastate entire tree restock areas. Following government bans on several insecticides due to environmental and health concerns, damage from these insects has been increasing. James Harrison-Moore, senior forest manager at Till Hill in northern England, explained that weevils can appear rapidly in restock areas, sometimes unnoticed at first. We typically plant around 2,700 young trees per hectare. Losing 10-15% in the first year is considered normal, but without intervention, entire areas can be wiped out, he said.

Agri-tech company Syngenta has introduced a new solution called Lanzarta, which uses a natural insecticide derived from the Ryania plant. When a weevil feeds on a treated tree, the insecticide targets a protein in its muscle cells, causing paralysis and eventually death. Importantly, Lanzarta only affects insects that consume the treated plants, leaving other animals unharmed. It received emergency authorization for use this year.

Andrew Crossthwaite, head of bioscience target selectivity at Syngenta, described the mechanism: the active ingredient opens ryanodine receptors in the insects muscle cells, releasing calcium and causing paralysis. This process effectively neutralizes weevils feeding on the tree.

Young Sitka spruce are particularly at risk because they take years to establish, unlike crops like wheat or barley which are only vulnerable for a few months. Restock areas are ideal for weevils, supporting their entire life cycle. Mature weevils are drawn to harvested stumps to lay eggs, and when young restock trees are planted, emerging weevils feed on them. This cycle peaks twice a year: in spring, when adults lay eggs, and in autumn, when offspring begin feeding, which is now the primary focus for spraying interventions.

The Confederation of Forest Industries warns that pine weevil damage is severe, often killing thousands of young trees. Estimated annual losses from these insects reach around 5 million, and dead trees also reduce carbon sequestration, impacting environmental efforts. Christopher Williams, CEO of the Royal Forestry Society, emphasized that managing pests like the pine weevil is vital for climate action, as healthy trees lock away carbon dioxide and contribute to long-term environmental sustainability.

Author: Zoe Harrison