Biological weed control to relieve millions from Ambrosia allergies in Europe

Globalisation has increased the rate of biological invasions, with invasive alien species (IAS) impacting biodiversity, ecosystem services, economies and public health. Despite known health effects from alien parasites, invertebrates and plants, few studies quantify their human health impacts, and existing estimates are often regional, disparate, or based on limited data, likely underestimating true costs. This study addresses this gap by quantifying the health burden of common ragweed (Ambrosia artemisiifolia) pollen in Europe and assessing the potential mitigation through biological control by the accidentally introduced beetle Ophraella communa. The research aims to estimate the number of affected individuals and associated economic costs, and to project reductions achievable via biological control, thereby informing policy and resource allocation for IAS management.

Previous work estimated global health costs of invasive species at USD 5.9 billion annually (Bradshaw et al.). European estimates of ragweed allergy burden have varied widely, with prior assessments (e.g., Bullock et al.) using lower per-patient treatment costs and fewer affected individuals (0.84–4.18 million), likely underestimating impacts. Lake et al. reported higher sensitisation totals, but their region-based approach contrasts with the present geospatial interpolation of sensitisation rates from numerous geo-referenced studies. The current study builds on these works by integrating extensive pollen exposure data, sensitisation datasets, and healthcare utilisation records, offering a more robust Europe-wide estimate and validating against detailed regional health data (Rhône-Alpes, France).

- Exposure mapping: Compiled mean seasonal total Ambrosia pollen integrals (2004–2012) from 296 European monitoring stations, interpolated to a 10 × 10 km grid covering EU27 and neighboring non-EU countries. Extracted exposure metrics per grid cell using the CGRS (ETRS89). - Sensitisation mapping: Systematically reviewed European studies to obtain (a) overall aeroallergen sensitisation in the general population and (b) ragweed sensitisation among sensitised individuals. Interpolated these data to the 10 × 10 km grid, then multiplied by grid-level population to estimate numbers sensitised. Adjusted for clinical relevance to estimate clinically relevant ragweed sensitisation and restricted to areas with recorded ragweed pollen exposure to derive the number of symptomatic patients. - Validation with regional health data: Used healthcare reimbursement data (anti-allergy/asthma medications, consultations, tests, desensitisation) from 313 communes in the Rhône-Alpes region (France) during the ragweed season to relate patient numbers to seasonal pollen integrals and validate Europe-wide estimates. - Cost estimation: Derived annual per-patient treatment costs from European sources (range €380–€8,060; median €565). Incorporated socio-economic costs of lost work using a medical-to-absence cost ratio (18.5) from Rhône-Alpes. Applied PPP-adjusted health expenditures (2015) to calculate total annual European costs. - Field experiment on pollen production: In Northern Italy (Po Plain), established plots at three sites (Corbetta, Grugliasco, Magnago) with insecticide exclusion of O. communa in replicated plots (where permitted) across 2015–2016. Used GLMMs to estimate effects of beetle exclusion on probability of raceme production and raceme length density, providing an estimate of pollen production reduction due to O. communa. - Species distribution modelling (SDM): Built SDMs for A. artemisiifolia and O. communa using global occurrences and WORLDCLIM bioclimatic variables. Employed Random Forests (with GLM/GAM/MaxEnt tested) to predict suitability. Estimated number of O. communa generations via growing degree days (GDD; field-derived threshold ≈2887) mapped across Europe. Overlaid beetle generational potential with ragweed pollen integrals to project reductions in pollen exposure and patient numbers once O. communa occupies its European environmental niche. - Impact quantification: Calibrated the relationship between seasonal pollen integrals and relative patient numbers using Rhône-Alpes data, then projected Europe-wide reductions in patients and PPP-adjusted costs after O. communa establishment. Also analysed long-term pollen records (2004–2018) at Milan-area sites to quantify real-world reductions in airborne pollen following beetle establishment.

- Pre-biological control burden: Approximately 13.5 million (CI 10.9–14.8 million) people in Europe suffered from seasonal ragweed pollen allergy prior to O. communa establishment, with total annual costs of about €7.4 billion (CI €5.4–€8.6 billion). - Sensitisation: About 23.2 million Europeans are ragweed-sensitised; after adjusting for clinical relevance, an estimated 15.8 million have clinically relevant sensitisation. - Field experiment: O. communa reduced pollen production of A. artemisiifolia by an average of 82% (range 73–100%) across Northern Italy sites, aligning with observed reductions in airborne pollen in the Milan area. - Observational evidence (Milan area): Marked declines in airborne ragweed pollen concentrations since O. communa establishment that are not attributable to meteorological variation. - Projected Europe-wide impact: Once O. communa colonises its suitable European niche, the number of allergy patients is projected to drop by approximately 2.3 million (≈16.9%), and annual costs to about €6.4 billion (CI €4.4–€7.5 billion), yielding savings of roughly €1.0–€1.1 billion per year. - Geographic benefits: Greatest additional benefits anticipated in Northern Italy (already observed) and parts of the Balkan Peninsula.

The study demonstrates that the health and economic impacts of common ragweed in Europe have been substantially underestimated and that biological control via O. communa can provide significant public health benefits. By integrating extensive aerobiological data, sensitisation prevalence, regional healthcare utilisation, and ecological modeling, the authors provide more accurate estimates of patient numbers and costs. The strong reduction in pollen production in field experiments and consistent declines in airborne pollen in Northern Italy support the causal role of O. communa. Projections suggest meaningful reductions in patient numbers and costs as the beetle spreads across climatically suitable regions. Importantly, host-specificity testing indicates minimal risk to non-target plants under field conditions, supporting a favorable risk–benefit profile for biological control. The results argue for incorporating human health costs more fully into IAS impact assessments and management planning, as doing so alters cost–benefit analyses and supports investments in biological control where appropriate.

This interdisciplinary assessment quantifies the substantial public health burden of Ambrosia artemisiifolia in Europe and shows that the biological control agent Ophraella communa can significantly reduce both patient numbers and economic costs. The findings suggest that current IAS cost estimates likely omit major health-related components, underestimating true societal impacts and the benefits of management. Future work should include comprehensive risk–benefit assessments of biological control agents, continued monitoring of O. communa spread and efficacy, refinement of exposure–response relationships across regions, and integration of health costs into broader IAS economic evaluations to guide policy and coordinated management.

- Data and interpolation: Sensitisation and exposure were interpolated from heterogeneous datasets; while validated in Rhône-Alpes, regional variability may remain and some areas have sparse monitoring. - Clinical relevance adjustment: Conversions from sensitisation prevalence to clinically relevant cases rely on literature-based ratios at country/region level, introducing uncertainty. - Cost estimates: Per-patient costs and the medical-to-absence cost ratio are derived from limited country/regional sources and adjusted via PPP; true costs likely vary by healthcare system and employment patterns. - Modeling assumptions: Projections assume O. communa will fully occupy its environmental niche and sustain impacts on pollen production; establishment, dispersal, and climatic interactions may limit or delay realised benefits. - Causality outside Milan: While Milan shows strong evidence, attribution in other regions is modeled rather than empirically observed; meteorological and land-use changes could confound local outcomes. - Conservative estimates: Authors note conservative calculations; both baseline burden and benefits may be under- or overestimated due to the above uncertainties.