Mosquito-borne diseases such as malariaW and Dengue feverW are dealt with by mosquito control or by medical treatment.
Mosquito control is clearly preferable in terms of human cost (suffering and death, plus a degree of discomfort from mosquito bites) and probably in economic cost as well. Some methods of mosquito control do not require the use of chemicals, and these should be used either in preference to, or (in serious cases) in addition to chemical methods. If chemical methods are used, it would be hoped they could be phased out as the problem is brought under control.