The chikungunya outbreak that affected Réunion and Mayotte in 2005–2006 triggered an unprecedented public health crisis due to its scale, its unexpected nature, the emergence of severe forms of the disease, and an impact on mortality that had not been previously documented. It may seem paradoxical that, amid intense public pressure to take every possible measure to curb the epidemic, the widespread use of insecticides sparked fears and skepticism among the population. Here we will review what has happened in Réunion in terms of assessing and managing the consequences of insecticide treatments. We will then examine whether similar questions are being raised in Europe as chikungunya makes its way into northern Italy and in the United States, which is grappling with the fight against the West Nile virus vector. (R.A.)