Mosquito Spraying in Hungary Cuts Pests but Also Kills Beneficial Insects

Every summer, municipalities across Central Europe fire up truck-mounted sprayers to fight mosquitoes, blanketing neighborhoods in a fine chemical fog that residents rarely think twice about. The technique, known as ultra-low volume or ULV spraying, releases tiny droplets of insecticide that drift through the air and knock down adult mosquitoes on contact. It is one of the most visible and widely trusted tools in public health pest management, and in Hungary it typically relies on deltamethrin, a synthetic pyrethroid often blended with an extract of the pyrethrum-producing chrysanthemum. Yet a fundamental question has lingered behind the routine: does this approach actually work in the field, and at what cost to the rest of the insect world? A new experimental study conducted in Hungary set out to answer both questions at once, and its findings reveal an uncomfortable trade-off between human comfort and insect conservation.

The research, published in PLOS Neglected Tropical Diseases, was led by László Zsolt Garamszegi and colleagues, who designed a rigorous field experiment to quantify, for the first time under real Central European conditions, how ULV spraying affects both target mosquitoes and the broader community of flying insects that share the same air. Rather than simply comparing sprayed and unsprayed areas at a single moment, the team employed a before-after-control-impact design, abbreviated BACI, which is considered the gold standard for detecting environmental impacts in field studies. In this framework, researchers sample sites both before and after a disturbance occurs, and they do so at both impacted and control locations. This four-way comparison allows scientists to separate genuine treatment effects from natural fluctuations in insect abundance that would occur anyway due to weather, season, or chance.

The technical logic of the BACI design matters because insect populations are notoriously variable. Mosquito numbers can swing dramatically from one night to the next depending on temperature, humidity, and wind, so a naive before-and-after comparison at a single sprayed site could easily mistake natural decline for chemical kill. By pairing treated sites with untreated controls and measuring change in both, the researchers could isolate the signal of the insecticide itself. Mosquitoes were monitored using BG Sentinel traps, a widely used sampling device that mimics the visual and olfactory cues of a human host and is particularly effective at capturing Aedes species, including the invasive tiger mosquito. Non-target flying insects, meanwhile, were collected with malaise traps, tent-like passive structures that intercept insects as they move through the landscape and provide an unbiased sample of whatever happens to be flying by.

When the results came in, the good news for mosquito control was real but qualified. ULV treatment produced a significant reduction in mosquito abundance at treated sites, with an average decline of approximately 47 percent. That is a meaningful drop, and it confirms that the technology is not merely theater: the fog genuinely kills a substantial fraction of adult mosquitoes in the treated zone. Importantly, the decline was proportional across both native mosquito species and invasive newcomers such as Aedes albopictus, the Asian tiger mosquito, and Aedes koreicus, two species that have been steadily expanding their range into Europe and raise concern because of their ability to transmit diseases like dengue, chikungunya, and West Nile virus. From a purely operational standpoint, the sprayers were doing their job against both established and emerging threats.

However, the study also revealed that the effectiveness of ULV spraying is far from uniform. The reduction in mosquito numbers varied substantially from site to site, and two factors emerged as key influences: the initial abundance of mosquitoes before treatment and the wind conditions at the time of spraying. This makes intuitive sense from an application standpoint. ULV droplets are extremely small, typically in the range of a few tens of microns, which allows them to remain airborne and drift through vegetation where mosquitoes rest. But the same property makes them exquisitely sensitive to air movement. Where wind carried the droplets away from their intended target zone, or where mosquito populations were so dense that a single pass could not make a dent, the treatment underperformed. For municipal operators, this suggests that timing applications to calm conditions and calibrating expectations to local population levels could squeeze more value out of every spraying campaign.

The more troubling half of the story concerns what else was flying through that chemical fog. Malaise trap samples revealed a marked decline in non-target flying insects at treated sites, with reductions exceeding 40 percent across multiple taxonomic groups. The damage was not confined to a single vulnerable lineage; it swept broadly through the insect community, hitting small and medium-sized insects particularly hard. This size bias has a plausible mechanistic explanation: smaller insects have greater surface area relative to their body mass, so they absorb a lethal dose of insecticide more readily from contact with droplets, and their smaller energy reserves give them less capacity to survive sublethal exposure. The pattern also held when the researchers considered pollinator taxa as a group, a finding with obvious implications for ecosystems that depend on insect pollination services.

The scale of the non-target impact deserves careful interpretation. A 40 percent or greater short-term reduction in flying insects is not a trivial side effect, especially when it recurs across a growing season in which municipalities may spray repeatedly. Insects underpin food webs as prey for birds, bats, and fish, and they provide essential services including pollination, decomposition, and pest suppression. While the study measured short-term impacts and cannot by itself establish long-term population consequences, the magnitude of the immediate effect suggests that a single ULV application sends a substantial shock through the local insect community, one from which recovery must occur before the next application arrives. Whether repeated cycles of impact and recovery accumulate into lasting damage remains a critical open question for future research.

The findings arrive at a moment of heightened public anxiety about insect declines. Reports of falling insect biomass across Europe have made headlines worldwide, and conservationists have increasingly pointed to pesticide use as a contributing factor. Against that backdrop, the Hungarian study offers a rare piece of hard, quantitative evidence about one of the most common pest control interventions on the continent. It does not conclude that ULV spraying should be abandoned; the 47 percent reduction in mosquitoes, including disease-capable invasive species, represents a genuine public health benefit that cannot be dismissed. Instead, the authors frame the results as a trade-off: vector control and insect conservation are both legitimate goals, and current practice imposes real costs on the latter in pursuit of the former.

That framing points toward practical improvements rather than a simple verdict. If treatment effectiveness depends on wind conditions and initial mosquito abundance, then smarter application protocols, including monitoring-based triggering, weather-aware timing, and targeted treatment of breeding hotspots rather than blanket coverage, could reduce the total insecticide load while maintaining or even improving mosquito suppression. The similar proportional declines observed in native and invasive mosquitoes also suggest that the insecticide itself is not selective, meaning selectivity would have to come from where, when, and how much is sprayed rather than from the chemistry. Integrating ULV spraying into an integrated vector management strategy, alongside larval source reduction and biological controls, could shrink the collateral footprint of each campaign.

For residents of mosquito-prone towns, the study is a reminder that the reassuring fog rolling down the street is a double-edged instrument. It demonstrably cuts mosquito numbers, including the invasive species now knocking at Europe’s door, but it also cuts down a large share of everything else with wings, from pollinators to the tiny insects that feed the birds. As climate change pushes Aedes albopictus and Aedes koreicus further north and lengthens the season during which spraying seems necessary, the tension documented in this Hungarian field experiment will only intensify. The study’s lasting contribution is to replace anecdote with numbers, giving policymakers, municipal operators, and conservationists a common factual foundation for deciding how much mosquito control is worth, and what the rest of the insect world is being asked to pay for it.

Subject of Research: Field evaluation of ultra-low volume deltamethrin mosquito spraying on target and non-target insects in Hungary

Article Title: The effect of ULV-based mosquito control on target and non-target organisms in Hungary: An experimental field study

Article References: Garamszegi, L. Z., Nagy, G., Klein, Á., Szentiványi, T., Vásárhelyi, Z., Markó, G., Zsebők, S., & Soltész, Z. (2026). The effect of ULV-based mosquito control on target and non-target organisms in Hungary: An experimental field study. PLOS Neglected Tropical Diseases, 20(10), e0014140. https://doi.org/10.1371/journal.pntd.0014140

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014140

Keywords: ULV spraying, deltamethrin, mosquito control, Aedes albopictus, Aedes koreicus, non-target insects, BACI design, pollinators, insect decline, vector management, Hungary, field experiment