Chemical Mosquito Control Also Harms Pollinating Insects, Study Confirms

The study focused on ground-based ultra-low volume (ULV) mosquito control, a method in which a very small amount of insecticide (deltamethrin) is dispersed into the air as an extremely fine mist. Treatments are typically carried out after sunset or at dawn, when mosquitoes are most active.

A key feature of the study is that it separately evaluated the effects of ULV spraying on native and invasive mosquito species. This distinction is important because it was previously thought that invasive mosquitoes – such as the Asian tiger mosquito (Aedes albopictus) and the Korean bush mosquito (Aedes koreicus) – may be less susceptible to conventional ground-based chemical control than native ones. Invasive species are primarily active during the day, tend to remain within relatively small areas, and often occupy sheltered, human-associated habitats, including dense vegetation, gardens and areas around buildings, where insecticide exposure is expected to be lower.

The findings, however, showed that both invasive and native mosquito populations declined to a similar extent in the short-term following treatment. This suggests that the current ground-based ULV approach is also effective against invasive mosquitoes, with no measurable difference in efficacy compared with that observed for native species.

On average, mosquito abundance in treated areas fell by approximately 45%. However, the effectiveness of the treatments varied considerably between sites: some locations showed substantial reductions, while others exhibited only minimal effects. Treatment efficacy was influenced by local environmental conditions, including wind and the initial abundance of mosquitoes.

Another important finding of the study is that ground-based ULV treatments are non-selective. Samples collected using traps designed for the capture of flying insects in general showed that these non-target organisms also declined significantly in treated areas, alongside mosquitoes. The greatest reductions were observed among small- and medium-sized insects, and pollinators, including hoverflies, bees and butterflies, were also affected.

"The ULV-based mosquito control method examined in this study presents a clear challenge from the sustainability perspective. While it reduces mosquito abundance in the short term, it may simultaneously cause comparable damage to communities of flying insects. For this reason, current practice should be reconsidered in order to find a balance between the desired effects and the ecological side effects. Greater emphasis should be placed on integrated mosquito management, that includes the elimination of breeding sites, the application of biological control methods and the implementation of more targeted interventions," said László Zsolt Garamszegi, Director General of the HUN-REN Centre for Ecological Research.

A major strength of the study is that it provides quantitative evidence under real-world Hungarian conditions, evaluating the effects of operational mosquito control practices. This is the first scientific assessment in Hungary to quantify the impacts of the most recent chemical mosquito control on both target mosquitoes and non-target insects under operational field conditions.

The authors emphasise that the aim of their research is not to advocate a particular position, but rather to provide an objective, quantitative evidence base for decision-making and future mosquito management strategies. Achieving this requires a comprehensive assessment of both the effectiveness of current practices against target mosquito species and their broader ecological consequences.

To support the development of such an integrated strategy, researchers at the HUN-REN Centre for Ecological Research have prepared a professional guidance document entitled Ecology-Based Mosquito Control: An Integrated Approach (only in Hungarian). This guideline summarises current mosquito control practices in Hungary, reviews biological control options, discusses the main challenges associated with existing methods, and presents recommendations for integrated, ecologically based mosquito management, incorporating the findings of the present study.

The full preprint describing the current research findings is available here.