Assessing the Sterile Insect Technique in Small, Non-Isolated Urban Areas: A Field Trial Against Aedes albopictus in...

The sterile insect technique (SIT) is considered a promising and environmentally sustainable tool for controlling Aedes albopictus. While current guidelines address its implementation in moderately large and partially isolated areas, evidence from small, fully urban and spatially connected environments remains limited. In 2025, we evaluated SIT in two municipalities in southern Switzerland, releasing sterile males in small (≈12 ha), non-isolated urban areas representing contrasting operational contexts within ongoing integrated vector management programs. Entomological responses were assessed using a spatial, distance-based framework integrating ovitrap-derived egg abundance and hatching rates from treated and surrounding zones, alongside adult female monitoring. Following releases, egg abundance declined within treated areas relative to surrounding zones, with model-based peak reductions of approximately 57% in Ascona and 67% in Losone. Egg hatching rates were also lower within treated areas, with estimated reductions of approximately 9% and 22%, respectively. For both indicators, spatial analyses revealed gradual distance-dependent patterns rather than abrupt boundary effects. No consistent pattern was detected for adult female abundance, likely reflecting limited sampling intensity. The spatial and temporal responses observed across the two study sites suggest that SIT may contribute to modifying local reproductive dynamics of Ae. albopictus even in small, non-isolated urban areas under operational conditions.