Effectiveness of the sterile insect technique in controlling Aedes albopictus as part of an integrated control measure: evidence from a first small-scale field trial in Switzerland.

Background: The invasive Asian tiger mosquito (Aedes albopictus) poses growing health risks across Europe. In Switzerland, a preliminary field trial was conducted to assess the feasibility of integrating the sterile insect technique (SIT) into existing integrated vector management (IVM), which includes breeding site removal and application of biological larvicides. SIT involves repeated releases of irradiated sterile males, which mate with wild females, producing non-viable eggs and leading to population decline.

Methods: Following a preliminary release test in 2022, a small-scale SIT trial took place in 2023 in Morcote, Switzerland. Approximately 150,000 sterile males were released weekly over a 45-hectare area throughout the entire mosquito activity season, from May to September. This SIT area also received routine IVM. Population dynamics were compared with a control area where only IVM was applied. Monitoring included egg counts, hatch rates, and adult female densities. Generalized additive mixed-effects models (GAMM) and generalized additive models (GAM) accounted for spatial, temporal, and random effects. Model selection used AIC, BIC, and Chi-square tests (significance at 5%).

Results: The SIT-treated area showed a significant mosquito population reduction. Egg counts dropped by 57% (GAMM regression coefficient: - 0.8513, P < 0.001), with temporal patterns differing between SIT-treated and control areas (P < 0.001). Egg hatch rates were also lower in the SIT area, with odds of hatching reduced by 1.24 log-odds units (P < 0.001). Adult female densities declined by 66% (regression coefficient: - 1.0818, P < 0.001). Spatial GAMs revealed heterogeneous effects: up to 90% egg reduction in the western release area, while the eastern edge, bordering untreated zones, showed up to 300% higher egg counts. Similar spatial trends were observed for hatch rates and adult females (P < 0.01). These findings highlight both the overall effectiveness of SIT and the influence of mosquito immigration on spatial patterns.

Conclusions: This trial demonstrated the potential of SIT as a complementary tool in Swiss vector control. Public interest and acceptance were high. To improve cost-effectiveness, further optimization of male production, sterilization, transport, and release processes is needed. Continued implementation over multiple seasons is recommended to enhance long-term effectiveness.