MIAMI (AP) — Genetically modified mosquitoes are being released in the Florida Keys in an effort to combat persistent insect-borne diseases such as Dengue fever and the Zika virus.

The Florida Keys Mosquito Control District and the Oxitec biotechnology company announced Thursday that release boxes, non-release boxes and netted quality control boxes are being placed this week in six locations.

Starting early May, less than 12,000 mosquitoes are expected to emerge each week for approximately 12 weeks. Keys officials approved the pilot project last year involving the striped-legged Aedes aegypti mosquito, which isn’t native to Florida.