Aquatic monitoring of the entomofauna of treated watercouses by the oncho control programme in Sierra Leone: summary

l. ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRTQUE DE L'OUEST ECOI'GICAL GROUP Sixteenth session Bouak€,. 25-27 J amtary 1995 ocP/vcu /HYBro/es.r ORIGINAL: English AQUATIC MONITORING OF TIIE ENTOMOFAI.]NA OF TREATED \ilATERCOIJRSES BY TIIE ONCHO CONTROL PROGRAMME IN STERRA LEONE (SUMMARY) D. THOLLEY The monitoring of the selected watercourses (Mongo, Rokel/Seli and Kaba) in Sierra L,eone hpd been initially carried out by the OCP Hydrobiological Monitoring Team. But sipce February 1992, the Sierra lrone Invertebrate Biology Team had been monitoring the"selected stations of these rivers, which had been larvicided since April 1989. These stations were Musaia on the Mongo, Makpankaw on the Rokel/Seli and Outamba on the Kaba. On the whole, three larvicides had been used rotationally during the period under review (i.e. November t993 to April 1994). These were: Abate, $naclofos and Bacillus thurineiensis (B.t. H-14). Analysis of the results was made in comparison with the results obtained since the inception of monitoring to assess if there was any impact on the faunistic diversity, to assess the physio-chemistry of the water and report on the exchange of experiences by the Hydrobiologists. The following observations emerged from such analysis: (1) There was the emergence of once rarely encountered species in either drift or surber samples. These were Afrobeatodes, Prosopistomatidae, Euthyplociidae and Caridina in all stations except Oligoneuriidae at Musaia. Relatively, there was a slight increase in the Drift Index and Number of Individuals and Taxa per Surber during this reporting period. (2) The numbers per surber, faunistic diversity and drift indices tend to increase as the water level reduces reaching their peak in March, sharply dropping in April, when the water level was very drop may be due to the use of hard Ichthyotoxic Tristichia srowth.N {'n ( ah' ^\ tv\ts- o o tr o) E oa poor (3) (4) 2 It still remains clearly established that Outamba had a higher faunistic diversity than either Musaia and Makpankaw. Musaia was the only station which had not been subjected to the use of Ichthyotoxic Herbs. Chironomidae still remained the dominant saxicolous ta,xa. The night drift continued to be dominated by the Ephemeroptera. This group dominated the day drift. A situation similar to periods of larviciding but different from period of suspension of larviciding (November 92 to April 93). Makpankaw was continually subjected to Ichthyotoxic Herbs before the assumption of larviciding to date. Chironomidae remained the dominant Sa:ricolous ta:ra. Tricorythidae and Hydropsychidae which had been significantly represented in 1989-1991/92 mairtained their low status as in L992/93 except in March when they accounted for over half of the benthic fauna. There was a change in the drift indices based on dominance. The diptera which was the dominant group in either day or night drift was second to Ephemeroptera during this reporting period. This situation was contrary to 1992/1993 data similar to treatment and pre-treatment data. Evidence had emerged that Outamba had been subjected to strong Ichthyotoxic herbs especially in April. The Tricorythidae, Hydropsychidae, Baetidae and Hydroptilidae which were poorly represented in either drift and surber samples at Makpankaw and Musaia were the dominant ta;ra. This situation was similar to previous data. There was relatively no change in the physio-chemical character of the water (November 1993-April 1994). The exchange-of-experiences mission to Cote d'Ivoire and Burkina Faso had allowed us to learn new methods of identification and data processing. (s) (6) (7) (8)