# Field implementation of the sterile insect technique against Aedes aegypti in Recife, Brazil: operational challenges and impact of release frequency on vector dynamics

## TL;DR

This study tested the sterile insect technique in Brazil to suppress Aedes aegypti mosquitoes, finding that more frequent releases led to better results.

## Contribution

The study demonstrates that increasing release frequency improves suppression of Aedes aegypti in urban settings.

## Key findings

- SIT 2× reduced egg/trap/day by 39%, hatch rate by 33%, and female abundance by 51%.
- Sterilization was effective with 35 Gy for pupae and 65 Gy for adults.
- Handling and transport reduced flight ability by up to 35 percentage points.

## Abstract

The sterile insect technique (SIT) is an environmentally friendly tool for suppressing Aedes aegypti populations. While promising in controlled settings, its application in large urban environments presents logistical and biological challenges. This trial focused on releasing sterile males, sent from a long-distance production facility to suppress the local mosquito population.

Sterile males of Ae. aegypti were mass-reared, irradiated, and transported 712.2 km from a central facility to Recife, Brazil. Releases were performed once (SIT 1 ×) or twice per week (SIT 2 ×). Entomological indices—including eggs/trap per day (ETD), hatch rate, induced sterility, and adult female abundance—were monitored through ovitraps and BG-Sentinel traps. Data were analyzed using generalized linear mixed models (GLMMs) and Bayesian time-series modeling (CausalImpact).

Dose–response experiments established that pupae required 35 Gy and adults 65 Gy to achieve > 99% sterility, with no difference between gamma and X-ray sources. Adult sterilization was effective across 24–96 h post-emergence, facilitating operational flexibility. Handling and transport reduced flight ability by up to 35 percentage points, highlighting cumulative stress effects. In field trials, SIT 1 × yielded limited suppression, with ETD values remaining similar to or higher than those of the control. In contrast, SIT 2 × produced consistent suppression, reducing ETD by 39%, hatch rate by 33%, and female abundance by 51%.

In this study, increasing the release frequency was essential to achieve significant model outcomes, representing varying degrees of mild suppression of Ae. aegypti in a complex urban setting. In Addition, male handling, chilling, and transport emphasize the need to reduce the exposure to these parameters by improving the protocols. These results highlight key areas for scaling SIT within integrated vector management strategies in tropical urban settings.

The online version contains supplementary material available at 10.1186/s40249-025-01393-7.