Annual report of the aquatic invertebrate team

PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST ONCHOCERCIAS]S CONTROL PROGRAMME IN WEST AFR]CA ECOLOGICAL GROUP Eighth session ocP /vcu /HYB]O/87.8ORIGINAL: FRENCH They Bouak6, 24-27 March 1987 ECOLOG]CAL MON]TOR]NG OF THE WATERCOURSES UNDER ANT]-BLACKFLY LARVICIDING ANNUAL REPORT OF THE AQUATIC ]NVERTEBRATE TEAM A. W. Yte SUMMARY Using the protocol established by the Programme in col-laboration with theEcological Group, four stations were visited during this monitoring canpaign.are: The changes in the daytime and night-time drift indices as well as in that of themean night-tine/daytime ratio are represented in Figures 2, 3, 4 ana-r In general, the values of the night-time drift indices are very high, speciallyat Entomokro and Semj-en. This has resulted in reratively high val-ues for the meannight-time/daytime ratio, thus indicating some balance in the environment. Faunistic analysis has shown the very marked predominance of three taxonomicgroups which represent 65/"-8o% of the fauna that drifted the whore year. They arethe Ephemeroptera (Baetidae, Caenidae), the Trichoptera (Ecnomidae, Hydropsychidae,Leptoceridae) and the Diptera-chironomidae. A massive presence of hydracarians wasnoted in June and JuIy this year at all the stations. The Elmidae represent up to 42"/" of the night-time drift fauna at Semj.en. Thefauna on the rock slabs was not very much diversified and was often composed, up to99"/", of Hydropsychidae. - Danangoro and Entomokro on the Marahoue; - Semien on the Sassandra; and - the Dabakala road bridge on the Nzi. Resul-ts and discussions {dditional s tudies A 48-hour drift cycle centred on a permethrin treatment was carried out atDanangoro' The results recorded confirm the short-term toxicity of the rarvicide onthe aquatic invertebrates, especially the Caenidae.