Keeping the number of blackflies down

The Yaounde initiative has been continuing to treat parts of the Sanaga River between Edea and Monatele to keep the numbers of blackflies as low as possible while minimising the number of treatments of larvicide in the river.  The data for 2012 and early 2013 show that where the river was treated the number of flies was generally below 50 blackflies per trap per day in contrast to upstream where the number of flies per trap were between 120 and 230 per trap per day.   In 2012, the river was treated four times [starting 16th March; 27th April; 13th; July, 9th November] and twice in 2013 [starting 25th January and 22nd March] on the basis of action thesholds rather than calendar spraying. This frequency contrasts with the weekly spraying done during the 25 year Onchocerciasis Control Programme over most parts of west Africa.

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  1. It is quite exact when you mentionned that where the river was treated, the number of flies generally decreased. But the main problem is still concerning the speed of reinfestation of the treated sites. The reinfestation is fast when the treated area is not extended down and uptream the main river (Sanaga River) nor when the tributaries are not treated at all.

    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!

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