Field Efficacy of Seven Nighttime Ultra-Low-Volume Spraying Strategies Against Aedes albopictus in Urban Green Spaces - Shenzhen City, Guangdong Province, China, October-November 2025.

INTRODUCTION: Daytime adult mosquito control in urban parks may disrupt public activities and constrain equipment movement. We evaluated whether nighttime ultra-low-volume (ULV) operations could reduce adult Aedes albopictus host-seeking activity in complex vegetation. METHODS: Descriptive field comparisons were conducted at three urban green-space sites in Shenzhen, China. Seven strategies were evaluated: ground ULV-only, unmanned aerial vehicle (UAV)-only, light- or wind-disturbance-assisted UAV, dual-insecticide UAV, and two coordinated ground-air regimens. Adult host-seeking activity was measured using protected human-bait collection, a modified human landing catch (HLC) procedure with full protective clothing and no skin exposure. Henderson-Tilton control-adjusted efficacy was the primary comparison, and direct reduction was used as a supporting measure. RESULTS: In the control-adjusted analysis, wind disturbance plus UAV spraying yielded the highest observed Day 1 efficacy, 91.7% (11/12). Ground-air coordinated dual-regimen ULV spraying yielded the highest observed overall efficacy, 75.9% (2,339/3,080). Dual-insecticide UAV spraying yielded efficacies of 77.8% (7/9) on Day 1 and 67.9% (112/165) overall. Ground-air coordinated same-regimen ULV spraying showed moderate control-adjusted efficacy, whereas ground ULV-only spraying produced negative estimates under the evaluated field conditions. CONCLUSION: Under heterogeneous field conditions, wind disturbance plus UAV spraying had the highest observed Day 1 adjusted efficacy, whereas ground-air coordinated dual-regimen ULV spraying had the highest observed overall adjusted efficacy. Site, period, and baseline differences limit causal comparisons among strategies.