Risk determination for non-target arthropods from outdoor space applications of mosquito adulticides

Outdoor space applications of ultra-low-volume (ULV) insecticides are widely used for adult mosquito management, but public concerns persist about their potential effects on non-target arthropods. Therefore, we conducted a systematic review and analysis to evaluate evidence from global peer-reviewed operational studies, field studies simulating operational studies, and modeled ecological risk assessments (ERA). A total of 38 articles met inclusion criteria, representing 43 distinct studies across multiple arthropod taxa and 10 insecticidal active ingredients. Study types comprised 25 field experiments, nine operational applications, and nine ERAs. We recorded the presence or absence of acute mortality effects on non-target arthropods and analyzed associations using Fisher's exact test and Firth logistic regression. Operational studies-representing large-scale, real-world mosquito control applications-had no deleterious effects across all taxa and insecticides. In contrast, field studies documented effects in 15 of 25 cases, although results were equivocal, with 10 studies finding no effects despite conditions favoring direct exposure (eg caged insects placed in the direct aerosol path). The ERAs showed mixed outcomes, most likely reflecting their intentionally conservative design. Study type was strongly associated with effect detection (P < 0.001), with operational applications significantly less likely to report effects. Overall, evidence suggests that risks to non-target arthropod populations from operational ULV mosquito adulticide applications are low, primarily due to reduced exposure from nighttime treatments, aerosol droplet characteristics (size and volume), rapid dispersal, and rapid breakdown. Increased emphasis on operational-scale research is needed to strengthen the understanding of risks for non-target arthropods.