Targeted, density-dependent sterile male releases to enhance Aedes aegypti population suppression in southern California

Abstract The establishment of Aedes aegypti in California, coupled with recent detections of locally transmitted dengue, poses an increasing risk of arboviral transmission and highlights the need for effective control strategies. Conventional approaches are often insufficient due to the cryptic and inaccessible breeding habitats of Ae. aegypti , underscoring the need for innovative tools such as the Sterile Insect Technique (SIT). However, SIT effectiveness depends on a complex interplay of biological, ecological, and operational factors, including release frequency, wild-to-sterile (W:S) ratio, and baseline mosquito density. Understanding how SIT performance varies across density gradients is thus critical for optimizing intervention strategies. This study evaluated the density-dependent effects of SIT releases on Ae. aegypti population suppression in southern California. A targeted SIT program was implemented over two years (2024–2025), involving biweekly releases of in-house reared male Ae. aegypti sterilized using a 55 Gy X-ray dose. A total of 31 sites were stratified into high-, medium-, and low-mosquito density categories based on 2023 baseline data and treated with wild-to-sterile (W:S) ratios of 1:100, 1:50, and 1:20. Adult Ae. aegypti populations were monitored weekly using BG-Sentinel traps and analyzed using a negative binomial generalized linear mixed model. Our results indicated that SIT implementation resulted in consistent and substantial Ae. aegypti population reductions across all density strata. In high-density areas, abundance declined by 59–78% in 2024 and up to 88% in 2025, while reductions in low-density areas were more modest in 2024 (19–43%) but increased in 2025 (38–71%), both compared to the baseline (2023). Aedes population suppression exhibited a dose–response relationship, but with diminishing returns at higher W:S ratios. These findings provide strong evidence that targeted SIT can achieve substantial and sustained suppression of Ae. aegypti populations, with effectiveness driven by both release intensity and mosquito density. The observed non-linear response supports the need for a shift from maximizing to optimizing W:S ratios by identifying context-specific “impact thresholds” that balance suppression efficiency with operational costs.