# Entomological surveillance for bluetongue virus in Poland: late-season activity and abundance of Culicoides vectors in 2024

## TL;DR

This study tracked biting midges in Poland during late 2024 to assess their role in spreading bluetongue virus, finding no active virus but highlighting ongoing transmission risks.

## Contribution

The study provides new insights into late-season Culicoides activity and vector distribution along livestock routes in Poland.

## Key findings

- Culicoides obsoletus/scoticus and C. punctatus were abundant, with high blood-feeding activity among females.
- No bluetongue virus RNA was detected in tested midge pools despite active vector presence.
- Environmental conditions and spatial variation influenced midge abundance and activity patterns.

## Abstract

This study focused on the seasonal activity and species diversity of Culicoides biting midges collected from 11 locations along the western border of Poland and major livestock transit routes, and included screening for bluetongue virus (BTV) RNA.

The sampling was conducted between September and November 2024. Collected biting midges were counted and identified to the species level. The gonotrophic forms of the females were also determined. Pools of insects were tested for the presence of BTV genetic material using a reverse-transcription quantitative real-time PCR.

A total of 13,022 individuals were identified. The results revealed spatial and temporal variation in midge abundance, likely influenced by local environmental conditions. A sharp decline in activity was observed after week 44, coinciding with decreasing ambient temperatures The widespread presence of Culicoides obsoletus / scoticus complex, recognised vectors of BTV, was confirmed along with high abundance of C. punctatus, a species considered a potential vector. All gonotrophic forms were identified, and 57.3% of females had taken a blood meal, indicating active reproduction and frequent host-animal contact throughout the sampling period. Pools of blood-fed, parous and gravid females were tested for BTV RNA, but all samples returned negative results.

Although no evidence of active BTV circulation was found, the presence of competent vectors and favourable autumn conditions highlights the potential risk of transmission. These findings underscore the need for continued entomological and virological surveillance to support early detection and control of BTV.