In fact, blackflies can fly to about 25 Km using their proper wings beat and up to hundreds kilometers under wind effect. But their concentrations in certain areas depend from the existence of favourable factors such as relative humidity or human concentrations, combined with existence of fly displacement corridors linked to the breeding sites line. Tributaries remain a major factor of blackfly reproduction due to numbers of breeding sites founded in some of them.

So it is clearly indicated to extend the treated area not only down and upstream in the main treated river, but also in the tributaries identified as to be productive for blackflies.

It is therefore necessary, while continuing good scientific monitoring of the blackfly control project as done by YIF, to have additionnal founds because the larvicides are not cheap!