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Trente ans de lutte contre l’onchocercose en Afrique de l’Ouest. Traitements larvicides et protection de l’environnement

 | 
Laurent Yaméogo
, 
Christian Levêque
, 
Jean-Marc Hougard

Références des articles présentés sur le cédérom / Papers references presented on CD-ROM

Effects of permethrin as Simulium larvicide on non-target aquatic fauna in an African river

L. Yaméogo, E.K. Abban, J.-M. Elouard, K. Traoré et D. Calamari

Résumé

The side-effects of permethrin (20% EC) as a Simulium larvicide on aquatic invertebrates and fish was studied under operational vector control conditions to contribute to the evaluation of the product for its possible adoption by the Onchocerciasis Control Programme in West Africa. After 15 weekly applications of the formulation at 0.045 litre per m3 of water discharge, drift samples virtually contained no Ephemeroptera. Saxicolous fauna density and proportional diversity were also affected. However, both drift and saxicolous fauna recovered to almost pretreatment levels a month after treatment was terminated. Fish showed some evidence of stress but remained in the active treated zone to make trends of catches in the area comparable with those of the control station. The treatment did not resuit in fish mortalities, and the condition of fish before and after the experimental period was significantly unchanged. Thus, operational use of permethrin by the Programme would not be expected to have permanent adverse effects on the non-target fauna.

Texte intégral

1Received 1 June 1992; accepted 3 January 1993

Introduction

2The use of insecticides against the larvae of Simulium has been the most successful method for the control of river blindness in the WHO (World Health Organization) Onchocerciasis Control Programme (OCP) in West Africa. Since the commencement of insecticide treatment in 1974, temephos, an organophosphate, has been the main insecticide used in OCP. Other insecticides used include chlorphoxim and the biological control agent Bacillus thuringiensis var. israelensis (B.t. H-14). This agent is used during the low water period (October to June) while the Chemical insecticides are applied from June/July to October/November.

3The ecological effects of these treatments have been studied extensively and three review papers have been published (Lévêque et al., 1988, Yaméogo et al., 1988; Lévêque, 1989), providing an evaluation of ten years of larviciding and monitoring. The conclusions were the following: “The results obtained after many years of treatment lead us to assume that the larvicide employed had little effect on the non-target fauna. Although the first application of temephos and chlorphoxim had a fairly strong impact on invertebrate communities in the short term, it would seem that these situations disappear fairly quickly after a year or less of successive applications”.

4Unfortunately, after several years of treatment, resistance to temephos (Guillet et al., 1980) and chlorphoxim (Kurtak et al., 1982) has been reported in some of the cytospecies of the Simulium damnosum complex. As a resuit of this, a number of carbamates and pyrethroids have been selected as alternatives, based on the toxicity against the vector, the relative harmlessness to the non-target fauna and also the type of formulation, the cost of utilization, mammalian toxicity and other considerations. Among the candidate larvicides, permethrin was selected in 1984 for potential operational use. A preliminary assessment of its impact on aquatic fauna in tropical conditions was made through acute toxicity tests on fish (Yaméogo et al., 1991) and by means of semi-field experiments in mini-gutters (Yaméogo et al., 1992). These experiments led to the conclusion that a pilot scale field trial was necessary before the insecticide could be used operationally.

5This paper is based on data collected during an operational control effort in an operational programme, hence the lack of repetition (low number of drift nets, Surber samples) and the difficulties encountered in completing the sampling programme. The first objective of the programme is to control the disease, so the aquatic monitoring is mainly carried out to detect important changes in the communities that could in the long run affect aquatic resources available to the human populations. The analyses in this paper have therefore been made with this in view.

Materials and methods

Description of the area

6The pilot operational trials were conducted on the Sassandra river in Côte d’Ivoire, one of the seven countries (Bénin, Burkina Faso, Côte d’Ivoire, Ghana, Mali, Niger and Togo) in the initial OCP area (Fig. 1) which covered about 654 000 km2 in West Africa. Since 1987/1988, the programme has been extended to four other countries (Guinea, Guinea Bissau, Senegal and Sierre Leone). The total area is now about 1 300 000 km2, but more than 80% of the initial OCP area is no longer being treated so the total length of rivers treated in the whole area is between 20 000 km and 25 000 km.

7The Sassandra has been under treatment since March 1979. It is a river which can reach flow rates of the order of 900 m3 s-1 at the height of its spate between August and November. During the operational trial conducted in 1984, however, flow rates fluctuated between 60 and 600 m3 s-1 (Fig. 2). The length of the section treated was 235 km. The permethrin dose used during the 15-week (August to November) trial was 0.045 1 of 20% emulsifiable concentrate (EC) formulation per m3. The effective carry of the product had been estimated at 5-10 km at the time of the operation. Therefore, based on the discharge and the number of potential Simulium breeding sites, the number of spraying points was between 27 and 38 per week. About 20-100 kg of active ingredient of permethrin were used weekly on the Sassandra.

8For the purposes of the study, three monitoring stations on the treated section of the river and a control site on a main tributary (Feredougouba or Bagbe river) were selected for the monitoring of non-target aquatic fauna (Fig. 3). The most downstream monitoring station was completely drowned and inaccessible for invertebrate monitoring after the first nine weeks of larviciding. Furthermore, only drift samples could be taken regularly at the other two stations because of the hydrological conditions.

Fig. 1. The Onchocerciasis Control Programme in West Africa, showing the zone studied.

Fig. 2. Trend of the discharges of the Sassandra at Sémien from 06/05/83 to 28/12/84.

Invertebrate and fish monitoring methodology

9Invertebrate. A battery of two nets (diameter, 12 cm) was used to estimate the abundance of drifting insects, which fluctuates, as in temperate zones, according to a circadian rhythm. This is low during the daytime and maximal one to two hours after sunset, and then the value decreases during the rest of the night (Elouard and Lévêque, 1977). Day drift, which is regarded as passive, is considered a reflection of the morbidity and mortality of the organisms. On the other hand, night drift, which is supposed to be mainly voluntary, reflects an active period. The measurement of drift during these two phases therefore reveals environmental differences. Schematically, a large day drift reflects an effect of external factors on the invertebrates. By contrast, a high night drift reflects an increase in densities of benthic organisms (Dejoux, 1977; Dejoux and Elouard, 1977; Statzner et al., 1985a,b, 1987). It is also reasonable to assume that drift increases with current speed. Therefore, most analyses were standardized by dividing by the filtered water volume the number of individuals captured in that water volume. The ratio is called the ‘drift index’ (DI), and expresses the number of individuals captured per m3 of water filtered by the nets.

10The quantitative evaluation of the benthic fauna of rock substrates was undertaken using a modified Surber sampler which covers an area of 625 cm2. The samples were taken in shallow riffles where Simulium damnosum breed. These are the areas which are subjected to direct and maximum impact of the larvicides. Therefore, the data collected give a direct indication of the effects of treatments, especially when pre-treatment data are available. Five replicates were normally used as the optimum number to give a reliable indication of variability without denuding the area. For each sampling date, the mean number of individuals per Surber and the 95% confidence limits were calculated, using the method described by Elliott and Décamps (1973) for small samples taken from a contagious distribution. For drift as well as for benthos, samples were taken 24 h before and 24 h after the weekly larviciding, when possible. The sampling frequency was reduced to once a month after the cessation of the operational trial.

Fig. 3. Location of the hydrobiological monitoring sites (*) according to accessibility and possibilities for the application of different monitoring techniques. The arrows show the limits of the section treated with permethrin.

11Fish. To estimate changes in species composition of catch and catch per unit effort of fishing (CPUE) in relation to the Chemical application, 60 h fishings were undertaken at experimental and control stations in connection with the first and eighth larviciding. The 60 h fishing at experimental stations consisted of three 12 h samples taken immediately before larviciding (from 18.00h two days before larviciding to 06.00h the day of larviciding) and two 12 h samples taken later (from 06.00h the day of larviciding to 06.00h the day after). At these stations, samples were taken between 0.5 and 1.0 km downstream of the larvicide application points. Samples obtained between 06.00h and 18.00h were classified ‘day’ as against ‘night’ samples obtained between 18.00h and 06.00h.

12A sample consisted of fish caught in a battery of gill nets, made up of seven pairs of different mesh sizes of nets (12.5, 15.0, 17.5, 20.0, 25.0, 30.0 and 40.0 mm mesh sizes). Each net had a surface area of 50 m2 and CPUE was estimated by the formula N x 100/(l x 2n x d) and W x 100/(l x 2n x d), where N is number of fish caught, W is the weight of fish caught in grams, l is the length of net in metres, d is the depth of immersion in metres, and n is the number of ‘nights’ or ‘days’ of fishing (Lévêque et al., 1988; Lévêque, 1989; Dejoux, 1980).

13Catches by small-mesh nets provide information on small-sized fish including juveniles. When they are great, recruitment can be considered satisfactory or normal. Low catches of this category of fish could signify either poor reproduction of the species or an effect of external factors on spawning or juveniles. A decrease in the catches of big-mesh nets is also of concern since it indicates potential impact on mature fish.

14Generally, natural, seasonal and interannual fluctuations are observed in multifilament gill-net catches. In the rainy season, for example, catches fall not only because of the difficulty of placing nets under good conditions due to water velocity but also because often nets catch fish on only some part of the water depth. They then increase with the decrease in water level. Furthermore, from year to year, catches can vary according to the hydrology and other abiotic and anthropic factors.

15Another factor studied during this trial was the coefficient of condition of the fish (K), or simply the ‘condition factor’, calculated from a formula of the type: K = W x 105/L 3, where W is the weight of fish in grams and L is the standard length of fish in mm. It allows an evaluation of the evolution of ‘fatness’ or general ‘well-being’.

Results and discussion

Invertebrate fauna

16Impact studies. Before the first permethrin treatment of the Sassandra, the mean daytime drift index was relatively high (11.3) at Guessabo, the furthest station below the section of the watercourse studied. The day-drift intensity was low at Sémien Ferry and Lenguekoro where the values obtained ranged between 0 and 2, thereby falling within the range of values generally recorded on untreated watercourses (0.2-4) as stressed by Dejoux (1978) and Yaméogo et al. (1988). The night drift was also high at Guessabo (30.3 individuals per m3 of filtered water) compared with that measured at Sémien Ferry and Lenguekoro. Despite these differences between the stations, the general trend of the drift index (Fig. 4) was comparable for all the stations and quite close to that described by Elouard and Lévêque (1977). Low during the daytime, the drift index increased after 18.00h, reached its maximum around 20.00h and decreased again up to 04.00h. The young stages of Baetidae, Caenidae and the Chironomini were encountered almost regularly in the pre-larviciding samples. By contrast, the Hydropsychidae, Philopotamidae, Tanytarsini, Orthocladiinae, Ephemeridae, Euthyplociidae, Prosopistomatidae and Oligoneuriidae were rare in this drift at Sémien Ferry, Lenguekoro and Guessabo (Okakro).

17After the first permethrin treatment, the drift intensity increased significantly (Fig. 5ad), by a factor ranging between 500 and 1,300 depending on the monitoring station and its location in relation to the larvicide’s spraying point.

18The drift was composed mainly of Ephemeroptera (Baetidae and especially Caenidae). Many other taxonomic groups were also present in the post-larviciding drift. The Ephemeroptera (e.g., Leptophlebiidae, Euthyplociidae, Ephemeridae and Heptageniidae), which were practically absent in the 24 h pre-larviciding drift samples, were collected in great quantities after the passage of permethrin. The same applies to the Trichoptera (Hydroptilidae, Ecnomidae and Leptoceridae). These observations were made at all the monitoring stations in the treated zone.

Fig. 4. Trend of the pre-larvicidal total fauna drift indices at Sémien Ferry for a 24 h period.

Fig. 5. The 48 h trends of the drift indices centred on the larviciding at Sémien Ferry and at Lenguekoro: (a) total fauna at Sémien Ferry, (b) Caenidae at Sémien Ferry, (c) total fauna at Lenguekoro, and (d) Caenidae at Languekoro, for the period 13-15/8/84.

19Of interest was the appearance after the larviciding of two drift peaks with high values within an interval of 2-5 h (Fig. 5a,c), depending on the site considered. In some of the cases (Sémien Ferry and Lenguekoro), the second peak was higher than the first one, but they were all influenced by the Caenidae. It should be noted that the larviciding was carried out after 15.00h and that the carry of the product (i.e., the distance over which it is effective), estimated at 5-10 km, was found to be between 10 km and 15 km. The night-time drift index rose from 31 to a maximum of 8,041 for the first peak and 1,040 for the second one at Guessabo. At Lenguekoro, it increased from an average of 9 to maxima of 2,977 and 5,488 for the first and second peaks, respectively, while at Sémien Ferry it rose from 1.9 to 68 and then 89.

Fig.5c 48-hr Trend of total fauna drift Indices centred on the larvicidlng at Lenguekoro: 13-15/8/84

Fig.5c 48-hr Trend of total fauna drift Indices centred on the larvicidlng at Lenguekoro: 13-15/8/84

Fig.5d 48-hr Trend of Caenidae drift Indices centred on the larvicidlng at Lenguekoro: 13-15/8/84

Fig.5d 48-hr Trend of Caenidae drift Indices centred on the larvicidlng at Lenguekoro: 13-15/8/84

20Permethrin caused a considerable increase in the drift intensity of most of the taxa. The catastrophic drift due to the pesticide seemed to have been increased by the nighttime biological-activity drift. The second peak could be related to the impact of a second wave of permethrin (the product’s carry having been underestimated) or to the drift of organisms from sites upstream or to a combination of the two factors. The acute toxicity of permethrin confirms what has been described by many authors for different pyrethroids vis-à-vis aquatic fauna in general and invertebrates in particular (Leahey, 1985a). The intensity of the drift caused by the second permethrin spraying reduced after the first week of larviciding. Moreover, the drift was increasingly composed of young stages, with the exception of the Elmidae (Coleoptera) and Chironomidae (Diptera), and the Ephemeroptera were almost absent.

21To evaluate the impact of the 15-week use of permethrin on the aquatic invertebrate populations under high-water conditions, the trend in the abundance of the fauna in place was assessed by considering the night-time drift (which indicates the density of the fauna in place). This night-time ‘biological activity’ drift measured for the total fauna the day before each spraying, (i.e., 6 days after larviciding) increased slowly after the decrease recorded before the second and third spraying cycles (Fig. 6). The rise of the curve of the total fauna was due essentially to the capture of Elmidae, Hydrae and Oligochaeta. The Ephemeroptera presented very low indices, almost nil during the permethrin larviciding period, reflecting their low abundance in the environment. Only the Chironomidae presented relatively stable indices and were considered less affected.

22The faunistic composition of the drifts collected before each larviciding remained more or less constant but differed from that observed before the first spraying. Thus, the Chironomidae constituted the greater part of the drift, the Baetidae, the Caenidae (Ephemeroptera) as well as the Trichoptera were rare and the Leptophlebiidae, the Tricorythidae and the Euthyplociidae (Ephemeroptera) were sampled only very rarely.

23The organisms collected during the operational trial were in general young larval stages from either old eggs hatching later or new eggs deposited by surviving adults or those from tributaries of other river basins not treated with permethrin. The recovery of aquatic invertebrate stocks under such conditions is therefore difficult.

24During the flood subsidence, the qualitative collections as well as the Surber sampling made at Lenguekoro and Sémien Ferry confirmed the rarity of the Ephemeroptera and the predominance of the Chironomidae (especially Chironomini) in the river (Fig. 7c). Recolonization study. Quantitative estimation of benthos was impossible during the highwater period, but Surber samples were taken during the flood subsidence. A survey carried out at the end of November 1984, only a few days after larviciding was stopped, made it possible to observe that at the starting point and at the end of the stretch treated the fauna were more diverse than at Lenguekoro and Sémien Ferry. The great number of potential breeding sites between these stations necessitated larviciding at fairly short intervals, which led to a considerable weekly impact on the aquatic invertebrates. At the time the operational trials were stopped, the densities of the saxicolous fauna at Sémien Ferry (the only station having pre-larviciding data) were low, compared with those for the same period in 1983 and to those of the control site (Fig. 7a-c), with a change in the structure of the community. Signs of recolonization were visible in December 1984 (Fig. 7d) only a month after the cessation of the trials. The Chironomidae (Chironomini and Tanytarsini) were still dominant, representing 91% of the fauna (Table 1), followed by the Hydropsychidae (Trichoptera) whereas, in December of the previous year, the Chironomidae represented only 45% of the aquatic invertebrates followed by the Simuliidae, the Leptoceridae and the Baetidae. The density and the structure of the populations were close to those of the same period in the previous year after 3-4 months’ suspension of any larviciding, but pollution from a sugar factory, which occurred in April/May 1985, interrupted the recolonization process. This type of pollution, which was severely felt by the Chironomidae, seems to have had a reduced effect on Ephemeroptera while Trichoptera were not affected by it (Fig. 7e,f). The density of the organisms was 136 and 175.4 individuals per Surber in April and May, respectively, as against 512 in January. It should be noted that the water became greenish due to a strong influence of algae density in it.

Fig. 6. Trend of the mean night-time drift indices measured the day before spraying at Lenguekoro.

25Unlike the Sémien ferry station, where the Ephemeroptera were absent from the Surber samples at the time the larviciding was stopped, this taxonomic group represented, during the same period, nearly 50% of the saxicolous fauna at N’Golodougou on the control station. The composition of the fauna was quite similar at the two stations in January 1985 (Table 1), only two months after the trial was stopped.

Fish fauna

26Variations in the catches per unit effort (CPUEs). A series of experimental catches was made at the different monitoring stations established for that purpose. Generally, Fig. 8a-c shows that reduced catches were recorded within the first week of permethrin application, as would be expected with continuous removal of fish from an area. By estimating population size by removal (Bower and Zar, 1977), it emerges that the decreases recorded are lower than those expected, except for the fish caught with 30 and 40 mm meshes. Decreases in CPUEs were observed during the trial period in the treated zone as well as in the control (Fig. 9) which were related to the discharge of the rivers. However, the fall in catches in the control zone was less than that in the treated section.

Abreviations
Bae: Baetidae
Cae: Caenidae
Ephe: Ephemeroptera (Total)
Psy: Hydropsychidae
Tricho: Trichoptera (Total)
Chi: Chironomini
Tat: Tanytarsini
Tap: Tanypodinae
Ocl: Orthocladiinae
Chiro: Chironomidae (Total)
S.others: Simulium others
Others: Other taxa
Fig. 7. Density (per 625 cm2) of the main taxa sampled before and after the permethrin trial on the Sassandra river in Côte d’Ivoire. Thin vertical bars indicate 95% confidence limits after a log (x + 1) transformation.

Table 1. Relative abundance and mean number of individuals per Surber collected at Sémien Ferry and N’Golodougou at the end of the trials and 2 months later.

Table 1. Relative abundance and mean number of individuals per Surber collected at Sémien Ferry and N’Golodougou at the end of the trials and 2 months later.

27After the larviciding was stopped (at the flood subsidence), the CPUE values recorded rose on all the stations. The trend of the catches of the main species made at Sémien (Fig. 10a,b) shows that the values recorded since the beginning of the permethrin larviciding of the Sassandra are (for the most part) greater than those for the same periods in 1983. The drought of 1982 and 1983, although not favourable for recruitment, did not interfere markedly with the use of permethrin. The return of better hydrological conditions led to an improvement in most of the catches despite the use of permethrin which, therefore, did not hamper the seasonal succession of catches.

28A comparison of species in samples at experimental and control stations before the first and eighth applications of permethrin showed that ‘new’ species in catches immediately before the eighth treatment were generally the same. Furthermore, the total number of species caught was quite stable during the trial. All the ‘new’ species caught except Malapterurus electricus and Polypterus endlicheri had been considered as fast migrating species by Baldry et al. (1981). This fact and their occurrence as ‘new’ species at the control station allowed their presence later at the treated sections of the river to be dissociated from the effect of the Chemical to a large extent. Although decreases in catches were recorded, the number of species did not vary fundamentally. It is therefore apparent that the ‘stress’ induced by the weekly permethrin applications has not caused the fish to flee from the treated zone. No mortality was recorded.

29The spraying was carried out during the spate. It is generally admitted that catches made during the low-water period (post-larviciding period in our case) are better than those of the spate period. While permethrin had an effect on the catches, it was masked by dilution. The evolution of catches in treated zones generally follows the seasonal cycle, with an increase in catches during the low-water period and a decrease during the spate.

30Variations in the coefficients of condition. Table 2 gives the coefficients of condition of the main species caught at Sémien. The results recorded before the first spraying as well as during and after the weekly larviciding do not show any notable differences. It appears that the larviciding had no detectable effect on condition.

Fig. 8. Trend in CPUEs of individual sizes of net (M) during the first week of permethrin application at (a) Lenguekoro, (b) Guessabo and (c) N’Golodougou.

Fig. 9. Time trend in total CPUEs in some monitoring stations during the trial.

  • a SD, standard deviation; Nb, number of individuals; BT, before the trial; DT, during the trial; AT, (...)

Table 2. Mean ‘condition’ (K) of main fish species caught at Sémien Ferry before and during the permethrin trial.a

Table 2. Mean ‘condition’ (K) of main fish species caught at Sémien Ferry before and during the permethrin trial.a

Fig. 10. Trend of catches of the main species made at Sémien from May 1983 to December 1984.

Conclusion

31In the short term, the entomic fauna were very much affected by the use of permethrin as a larvicide. The impact was not reduced by the high discharge, and recurred with more or less the same degree week after week. Only the Chironomini (Diptera) were tolerant.

32After 15 weekly larviciding cycles, permethrin led to changes in the composition of the lotic invertebrate populations of the Sassandra. Nonetheless, the existence of an upstream reach and untreated tributaries facilitated recolonization which was already quite marked only a month after the cessation of the trials. Four months later, after the replacement of permethrin by Teknar, the reconstitution of the fauna was almost complete but pollution independent of OCP activities interfered with the colonization of the benthic fauna.

33As regards the fish fauna, no direct mortalities attributable to permethrin were observed. Under natural conditions the dose at the spraying points could be 10-20 times the operational dose (0.015 mg l-1 x 10 min), therefore a level of concentration of 0.150-0.300 mg l-1 could be present for a few minutes while the 24 h LC50 is 0.040 mg l-1 (Yaméogo et al., 1991). However, exposure to high concentrations during the spate period will always be short, since the fish can flee from the larvicide wave and bioavailability is reduced by sorption on suspended solids. In fact, due to the high log Koc, (5.9), permethrin has an elevated affinity for suspended solids present at high level during the flood, and it is well known that toxicity is greatly reduced under such conditions (Hill, 1985). No bioaccumulation could be expected despite the high potential for partitioning (log Kow 6.1), as permethrin is quickly metabolized and excreted by many organisms including fish (Leahey, 1985b).

34In the medium term, the product did not seem to affect gill-net catches. Taken as a whole, the decrease observed during the spate followed the seasonal evolution with increase in catches during the low-water period. As regards the coefficients of condition of the main species no incidence of the larviciding on the fatness and therefore on the feeding of the fish was observed. The relatively high toxicity of permethrin on invertebrates has been confirmed by different laboratory tests. However, medium-term trials under field conditions show that under certain conditions the effects are reduced and recolonization takes place quite rapidly among the most affected organisms. This reversible impact of permethrin at high water and, particularly, its efficacy on blackfly species resistant to the organophosphorus compounds and the relatively low cost of its use (US $16 per kilometre of river treated between 100 and 150 m3 s-1 as against US $20 for Abate) have led to its selection as a replacement for Abate. However, any use of this product should be subject to close monitoring in addition to rigorous control of the larviciding conditions; also, the number of treatment cycles should be limited.

Acknowledgements

35This work was fully financed by the WHO Onchocerciasis Control Programme. We are grateful to the Programme Director, Dr E.M. Samba, and the Chief of the Vector Control Unit, Dr D. Quillévéré, who accepted the publication of this document. We thank the OCP Ecological Group also for having inspired and supported the preparation of this article.

Bibliographie

References

Baldry, D.A.T., Everts, J., Roman, B., Boon von Ochssee, C.S. and Lavéissière, C. (1981) The experimental application of insecticides from a helicopter for the control of riverine populations of Glossina tachinoïdes in West Africa. Part VIII: The effect of two spray applications of OMS-570 (endosulfan) and OMS-1998 (decamethrin) on G. tachinoïdes and non-target organism in Upper Volta. Trop Pest Management 27 (1), 83-110.

Bower, J.E. and Zar, J.H. (1977) Field and Laboratory Methods for General Ecology. Dubuque, Jowa: W.M.C. Brown.

Dejoux, C. (1977) Action de l’Abate sur les invertébrés aquatiques. III: effets des premiers traitements de la Bagoué. ORSTOM, Bouaké 14, 31 pp. multigr.

Dejoux, C. and Elouard, J.-M. (1977) Action de l’Abate sur les invertébrés aquatiques. IV: cinétique de décrochement à court et moyen termes. ORSTOM, Bouaké 4, 33 pp. multigr.

Dejoux, C. (1978) Action de l’Abate sur les invertébrés aquatiques. V: effets des premiers traitements de la Maraoué. ORSTOM, Bouaké 19, 9 pp. multigr.

Dejoux, C. (1980) Effets marginaux de la lutte chimique contre Simulium damnosum. Techniques d’études. ORSTOM, Bouaké 34, 64 pp. multigr.

Elliott, J.-M. and Décamps, H. (1973) Guide pour l’analyse statistique des échantillons d’invertébrés benthiques. Annls Limnol 9(2), 79-120.

Elouard, J.-M. and Lévêque, C. (1977) Rythme nycthéméral de dérive des insectes et des poissons dans les rivières de Côte d’Ivoire. Cah. ORSTOM Hydrobiol. 11(2), 179-83.

Guillet, P., Escaffre, M., Ouedraogo, M. and Quillevere, D. (1980) Mise en évidence d’une résistance au téméphos dans le complexe Simulium damnosum (S. sanctipauli et S. soubrense) en Côte d’Ivoire (Zone du Programme de Lutte contre l’Onchocercose dans la Région du Bassin de la Volta). Cah. ORSTOM Entomol. Med. Paraistol. 17, 291-99.

Hill, I.R. (1985) Effects of non-target organisms in terrestrial and aquatic environments. In Leahey, P.J. ed. The Pyrethroid Insecticides, pp. 151-262. London: Taylor & Francis.

Kurtak, D., Ouedraogo, M., Ocran, M., Barro, T. and Guillet, P. (1982) Preliminary note on the appearance in Ivory Coast of resistance to chlorphoxim in Simulium soubrense/santipauli larvae already resistant to temephos (AbateR). WHO unpublished document WHO/VBC/82.850.

Leahey, P.J. (1985a) The Pyrethroid Insecticides. London: Taylor & Francis.

Leahey, P.J. (1985b) Metabolism and environmental degradation. In Leahey, J.P. ed. The Pyrethroid Insecticides, pp. 263-342. London: Taylor & Francis.

Lévêque, C., Fairhurst, C.P., Abban, E.K., Paugy, D., Curtis, M.S. and Traoré, K. (1988) Onchocerciasis Control Programme in West Africa. Ten years monitoring of fish populations. Chemosphere 17, 421-40.

Lévêque, C. (1989) The use of insecticides in the Onchocerciasis Control Programme and aquatic monitoring in West Africa. SCOPE 317-35.

Statzner, B., Dejoux, C., and Elouard, J.-M. (1985a) Field experimentation on the relationship between drift and benthic densities of aquatic insects in tropical streams (Ivory Coast). I. Introduction: review of drift literature, methods, and experimental conditions. Revue d’Hydrobiologie Trop 17, 319-34.

Statzner, B., Elouard, J.-M. and Dejoux, C. (1985b) Field experimentation on the relationship between drift and benthic densities of aquatic insects in tropical streams (Ivory Coast). II. Cheumatospyche falcifera (Ulmer) (Trichoptera: Hydropsyhidae). J. Anim. Ecol. 55, 93-110.

Statzner, B., Elouard, J.-M. and Dejoux, C. (1987) Field experimentation on the relationship between drift and benthic densities of aquatic insects in tropical streams (Ivory Coast). III. Trichoptera. Freshwater Biol. 17, 391-404.

Yaméogo, L., Lévêque, C., Traoré, K. and Fairhurst, C.P. (1988) Dix ans de surveillance de la faune aquatique des rivières d’Afrique de l’Ouest traitées contre les simulies (Diptera: Simuliidae), agents vecteurs de l’onchocercose humaine. Naturaliste Can. (Rev. Ecol. Syst.) 115, 287-98.

Yaméogo, L., Tapsoba, J.M. and Calamari, D. (1991) Laboratory toxicity of potential blackfly larvicides on some African fish species in the Onchocerciases Control Programme area. Ecotoxicol. Environ. Safety 21, 248-56.

Yaméogo, L., Elouard, J.-M. and Simier, M. (1992) Typology of susceptibilities of aquatic insect larvae to different larvicides in a tropical environment. Chemosphere 24(12), 2009-20.

Notes de fin

a SD, standard deviation; Nb, number of individuals; BT, before the trial; DT, during the trial; AT, after the trial.

Table des illustrations

Légende Fig. 1. The Onchocerciasis Control Programme in West Africa, showing the zone studied.
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Légende Fig. 2. Trend of the discharges of the Sassandra at Sémien from 06/05/83 to 28/12/84.
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Légende Fig. 3. Location of the hydrobiological monitoring sites (*) according to accessibility and possibilities for the application of different monitoring techniques. The arrows show the limits of the section treated with permethrin.
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Légende Fig. 4. Trend of the pre-larvicidal total fauna drift indices at Sémien Ferry for a 24 h period.
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Légende Fig. 5. The 48 h trends of the drift indices centred on the larviciding at Sémien Ferry and at Lenguekoro: (a) total fauna at Sémien Ferry, (b) Caenidae at Sémien Ferry, (c) total fauna at Lenguekoro, and (d) Caenidae at Languekoro, for the period 13-15/8/84.
URL http://books.openedition.org/irdeditions/docannexe/image/29295/img-5.jpg
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Titre Fig.5c 48-hr Trend of total fauna drift Indices centred on the larvicidlng at Lenguekoro: 13-15/8/84
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Titre Fig.5d 48-hr Trend of Caenidae drift Indices centred on the larvicidlng at Lenguekoro: 13-15/8/84
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Légende Fig. 6. Trend of the mean night-time drift indices measured the day before spraying at Lenguekoro.
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Légende AbreviationsBae: BaetidaeCae: CaenidaeEphe: Ephemeroptera (Total)Psy: HydropsychidaeTricho: Trichoptera (Total)Chi: ChironominiTat: TanytarsiniTap: TanypodinaeOcl: OrthocladiinaeChiro: Chironomidae (Total)S.others: Simulium othersOthers: Other taxaFig. 7. Density (per 625 cm2) of the main taxa sampled before and after the permethrin trial on the Sassandra river in Côte d’Ivoire. Thin vertical bars indicate 95% confidence limits after a log (x + 1) transformation.
URL http://books.openedition.org/irdeditions/docannexe/image/29295/img-9.jpg
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Titre Table 1. Relative abundance and mean number of individuals per Surber collected at Sémien Ferry and N’Golodougou at the end of the trials and 2 months later.
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Légende Fig. 8. Trend in CPUEs of individual sizes of net (M) during the first week of permethrin application at (a) Lenguekoro, (b) Guessabo and (c) N’Golodougou.
URL http://books.openedition.org/irdeditions/docannexe/image/29295/img-11.jpg
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Légende Fig. 9. Time trend in total CPUEs in some monitoring stations during the trial.
URL http://books.openedition.org/irdeditions/docannexe/image/29295/img-12.jpg
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Titre Table 2. Mean ‘condition’ (K) of main fish species caught at Sémien Ferry before and during the permethrin trial.a
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Légende Fig. 10. Trend of catches of the main species made at Sémien from May 1983 to December 1984.
URL http://books.openedition.org/irdeditions/docannexe/image/29295/img-14.jpg
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Auteurs

© IRD Éditions, 2003

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