The article contains the following sentence: "In a randomized trial in Singapore, releases of Wolbachia-infected males cut mosquito populations by 85 percent compared to control areas and dengue infections by roughly 70 percent."

There are different things you can do to mosquitos with different techniques. The article discusses several different techniques. Some eliminate disease-spreading mosquitos, some eliminate the mosquitos. In Singapore, the latter was tried out. It is not the case that Singapore used chemicals.