Incidence on non-target insect fauna of the alternate use of three insecticides (temephos, chlorphoxim and B.T. H-14) for the control of the larvae of simulium damnosum S.L.

WORLD HEALTH ORGANIZATION ORGANISATION MONDIALE DE LA SANTE Chlorphoxim (an organophosphate conPound) 'for Ehe non-targeE fauna (Dejoux & Troubat L9793 Gibon & Troubat, 1980; Dejoux et a currently used in the rainy season in cert cies S. sancti uli and \ ocP/vcu/HYBTO/ 84.4 ORIGINAL: FRENCH ONCHOCERCIASIS CONTROL PROGRAMME - AQUATIC MONITORING INCIDENCE ON NON-TARGET INSECT FAUNA OF THE ALTERNATE USE OF THREE INSECTICIDES (rernephos, chlorphoxim and B.r. H-14) FOR THE CONTRoL OF THE LARVAE OF SIMULIUM DAI'iNOSLI'I s. 1. by J..M. ELOUARDI F. M. GIBON1 1. INTRODUCTION The Onchocerciasis Control Prograrme in the Volta basin area (OCP) was launched in Decenber 1974. Under this prograrmre onchocerciasis transmission is halced by limiting Ehe populations of the complex of ,""tor species: Simulium damnosum. Weekly application of insecticiae ro rivers breaks the development cycle of these blackflies by killing their larvae, which are dependent on a lotic environment. Temephos or AbateR (organophosphorus compound) was selected on account of its many- qualitiesl particularly its-effi"""y against lhe lar*rae of the vector and its low toxicity ior non-target fauna. This insecticide has been applied by OCP since the end of. L974. Nevertheless, in December 1979 temephos resistance developed in the species S. souPTgnse and S. sanctipauli in breeding sites on the lower Bandama. This resistance sPread rapidly to ttr" ilZliffiffie forest zone and part of the humid savanne zone in the rainy season. Consequently, insecticides other than temephos have been used for controlling the larvae of S. dannosum s.1. so as to maintain efficacy. The replacement larvicides are: B.t. H-14, an insecticide of biological origin, which is toxic almost exclusively 6? blactfly larvae. Unfortunately it can be used only in the dry season because of the low concentration of active ingredient which makes it unusable in the rainy seeson, aE any rate with the logistic resources available to OCP. controlling the sPe which is much more toxic than temephos ,1976; Dejoux et al., 19811 Statzner,1., 1982). In spite of this it is ain parts of the Prograrmne area for S. soubrense. 1 R..".."h worker, oRSToM, 7o-74 route dtAulnay, 93140 Bondy, France. J I ,l The issuc of this document does not constitute formal publication. lt should not be reviewed, abstracted or quoted without the agreement of the World Health Organization. Authors alone are responsible for views expressed in signed articlcs. Ce document ne constitue pas une publication. ll ne doit faire l'objet d'aucun compte rendu ou rdsumd ni d'aucune citation sans l'autorisation dc l'Organisation mondiale de la Santd. Les opinions exprim6es dans les articles signds n'engagent quc leurs auteurs. ocP/vcu/HYBrol 84 .4 Page 2 Depending on locality and season, OCP uses temephos, chlorphoxim or B.t. H-14. The use of an insecticide on a given river is governed by the hyirological season-;;d by the Presence or otherwise of Eemephos-resistant species. Quite a lot is now knosn abouE the short-term and long-term impact of temephos, chlorphoxim and B.t. H-14 on the non-target fauna, but the long-term impact of alternating these three insecticides cannot be predicted. Two opposing hypotheses can be put forward: - the three insecticides produce drastic effectson different taxonomic S,rouPs; alternation would permit the regeneration (recolonization) of groups partly elininated by the use of a single insecticide. It would therefore be generally beneficial to the lotic ecosystems treated with anti-blackfly larvicides; - conversely, in view of the seasonal presence of different taxa, the alternation of the three insecticides (or of only Ewo of them) would have an even more catastroPhic effect on the whole of the non-target fauna; the most severe impacts would be cumulaEive. The purpose of the presenE report is to test these two hypotheses. It Eust be sEressed from the outset Ehat this objective will be difficult to achieve on account of: - the wide variationsin river 1evel from year to year, which affect t,he population dynamics of insects and produce variations in population distribution', the irregular alternation of the use of three insecticides; the insufficient amount of data available on this problem at the present time. 2. STUDY AREA, MATERIALS AND METHODS 2.1 Study area From all the siEes within the OCP area for monitoring the impact of insecticides, selected only those rocated on the lower Maraou6 (stations 8 and 16) in rvory coast' choice was based on Ehe following criEeria: we This the lower Maraou6 has been monitored since Ehe start of OCP, i... since 1975; - however, it has been treated with insecticide only since March 1979. For this river therefore.we have daEa collected both before and after the start of larviciding, which is the not the case for the majority of the rivers situated in the phase I and II areas of OCP; - many supplementary hydrobiological studies have been conducted on this river. Ihese provide a thorough knowledge of the systematics and ecology of the aquatic insect species and of the development of their comrunity strucEures. It is pointed out that the Danangoro site (station 8) has been monitored since 1975, while the Entomokro site (llo. t0) has been monitored only since }tarch 1977. The locations of these sites are shown in Fig. 1. 2.2 Sampling method Of Ehe sarnpling methods substraEes) we have selected alternation of insecticides, resulEs (E1ouard, 1983). tt i.e. the saxicolous fauna. used for river monitoring (day and night drift, artificial only the Surber sampler device for studying the impact of the because this is the method which provides the most reliable takes samples of the fauna colonizing Ehe rocky substrates, ocP/vcu/HYBro I 84.4 Page 3 For Ehe purposes of supplemented by samPles was only done, however, this study Ehe samples collected under the rnonitoring programne-were from the sa*e sites which were taken for other exPerimenEs. This r^rhen there was a gap in the chronological sequence of sampling' 2.3 Larviciding The general timetable for the use of the different insecticides (temephos, chlorPhoxim, B.t. H-14, used on the lower Maraou6 is shown in Fig. 2. Temephos was used on chis river ilitto,rt interruption from March 1979 to August 1980. Alternation of insecticides began only in November 1980, in accordance with the sequence shown in Fig. 2. 2.4 Hydrology The variaEions in water leve} were measured at the Bouafl6 river gauge. A11 Ehe readings are shown in Fig. 3. 2.5 Presentation of results Variations in abundance: these are represented as total numbers. Separate figures for "achffieengivenforthemajortaxonomic8rouPs:EpheueroPtera,TrichopEera and Chironomidae. The results for families and tribes from sites 8 and 16 were combined and are reported as averages. The months of December, January, February and March are joined by thick lines; these are the most thoroughly studied monEhs. The other months are joined by dotted lines. Structural variat,ions : these were monitored with the aid of the biocoenoEic index of 1982) wtrich was calculated from the mean values Per sample.pollution (Elouard & Jestin, 3. RESULTS 3.1 Total fauna Danangoro site The insect density at this site tends to be higher during the period Ereated with insecticide. The peak densities were observed during the periods of falling vrater leveIs when remephos (1980) and B.t. H-14 (1982) were applied weekly (fig.4). During the period when no insecticide was appfiea, L979 rras the only year wtrich showed fauna densiEies comparable to those observed during the period of larviciding. Entomokro site The phenomenon observed at the Danangoro site is even more marked here: the fauna was substantially more abundant during the period when insecticides were applied than during the period when they were not. The highest fauna levels were recorded in f981 (Fig. 5.). In view of these results it could be concluded that the application of insecEicides has a beneficial effect for the insect fauna as a whole. Against Ehis somewhat surprising result should be set the study of the impact of insecticides on Ehe composition of corununities and on the various taxa of which they are composed. 3.2 Pollution index The biocoenotic index of pollution (Elouard & Jestin, 1982) was applied to the mean of the monthly samples. It should be borne in rnind that this index Iras proposed for the surveillance of African rivers in order to Eonitor the strucEural changes brought about by repeated applications of temephos to rivers. Although this index was defined for the months of December, January, February and March and for temephos, we have calculated it for all mont.hs in order to monit.or its general trend, whatever the insecticide used. ocP/vcu/HYBrol 84.4 Page 4 Danangoro site During the period when insecticide was not applied the index obtained for the four months of falling water levels (except for January L976) was consistently below 6, Ehe value regarded as the limit for variations due to natural facEors (Fig.6) (Elouard, 1983). When insecticides are applied the values of the index for the same months are much higher, exceeding 5 and 6 except for the month of December in 1979 and 1980 (Fig. 6). Entomokro site The phenomenon reported for Danangoro site is even more marked for EnE.omokro during the larviciding period, the only value below 6 being that for I'larch 1979 (start of larviciding)(Fis. 7 ) . We therefore conclude that there is a change in fauna structure at these E.wo sites during the period when insecticides are applied. It should be noted that the values obiained in 1982 and 1983 following the alEernation of insecticides are no different from those obtained when temephos was used on its own (fig. O and 7). 3.3 Impact on the talq 3.3 . 1 Trichoptera Danangoro site At this site (rig. 8): - there were wide variations from year to year in TrichopEera densiEy during the period when insecticides were not applied. - the maximum Trichoptera density was obtained in 1980, when Ehe river was treated with temephos. The second highest value was obEained in 1981, when the river was stilI treated with ternephos but was previously subjected to several cycles of treatment with chlorphoxim. - the Trichoptera density was low in 1982 and 1983r years when Ehere were many changes of insecticide. However, it is noE possible to tell from Ehe results whether this was due to natural varialions in density such as were observed during the non-larviciding period or Eo the impacE of chlorphoxim and B.t. H-14, or to the alternation of Ehe three pesticides. EnEomokro site The overall abundance of Trichoptera at this site during t.he period of insecticide application is either as great as or greater than that observed during the untreated period. The maximum density was observed in 1981. It is also noted that the numbers collected in 1982 did not differ greatly from the numbers collecEed in 1979 and 1980 (Fig.9). In the light of the relatively stable results obtained at Entomokro it would seem that the variations in density obtained at Danangoro are due more to seasonal facEors than to the impact of the insecticides. Hydropsvchidae It should be borne in mind that in lotic environments the Hydropsychidae form the najority of the saxicolous fauna of the order TrichoPEera. ocP/vcu/HYBL}l 84.4 Page 5 It appears thati the density of these taxa is at its peak during the periods of falling urater leveIs and low vrater level wtren temephos is applied (1980 and 1981) (Fig. 10). the density \{as much lower in 1982 but remained quite comparable to, if noE. higher than, that obtained during the period preceding larvicide application. Here again we conclude that the impact of the alternation of insecticides on the overall density of Ehis Eaxon is noE zero. 3.3.2 Ephemeroptera Danangoro siE.e The density of the Ephemeroptera as a whole on the rocky substrates at Danangoro site was extremely variable from one year to another during the period before larviciding. It would seem that. during this period there rras some correlaE,ion between the density of this group and preceding high water level (when Figs. 2 and 11 are superimposed). Nevertheless this hypothesis is partly disproved by the densities recorded in 1978. During the period wtren insecticides were applied the fauna density was aE its peak in 1980, i.e. during the first season of falling water levels when temephos alone was applied. It should be noted that the high water level on the Maraoud was above normal during Ehe 1979 rainy season. The density of this taxonomic group was much lower in the following years and was at its lowest under treatment with B.t. H-14 following a long campaign of chlorphoxim treatmenE. The overall density appeared to increase again in early 1983, a period when the river was not treated with insecticide following a cont.rol campaign using chlorphoxim during the previous rainy season (fig. 11). Nevertheless, iE will be noticed that the minimum densities obtained during the period of treatment with insecticides are of the same order of magnitude as those observed when insecticides rrere not applied. The lowest density in 1982 may just as well be due to the considerable natural variations which seem to occur in this group as Eo the impact of the insecticides, or to the two phenomena combined. Entomokro site At this station the variations in density do not seem to be connected at all with the variations in high water level. 0n the other hand, the density of Ehis taxonomic group is greatly reduced by the insecticides, whichever are used. IE is difficult to synthesize the results obtained for the EphemeropEera group at these two sites. It can be noted, however, that there are great variations in abundance from year t.o year and that there is a tendency for densities to fa1l during the period when insecticides are applied; here an exception must be urade for the period of falling water levels at Danangoro in 1980. In order to throw more light on these results we shall study t.he effect of the insecticides and the alternation of insecticides, on the Ephemeroptera families which are mosE abundant, i.e. the Baetidae, the Caenidae and the Tricorythidae. Baetidae The fol lows same a9 larvae of this group account for the majority of the lotic Ephemeroptera. It from this Ehat the variations in density observed for chis family are roughly the those observed for the Ephemeroptera as a whole. Accordingly Ehere is (fig. f:): - a wide variation in abundance from year to year during the period when no insecticides were applied; a record abundance during the period of falling water levels in 1980, following l0 months of ternephos treatment and above-normal high water level; , ocP/vcu/HYBrol 84.4 Page 6 - an increasingly greaE reduction in the abundance of this group from year to year. Caenidae On the whole this family does not seem to be affected by the insecticide applications or by the alternation of products, because the following are noted (fig. i4); - a high variation from year to year during the period preceding the larviciding; - above-normal abundance in 19811 - low abundance in 1982, followed by high abundance in 1983. Tricorythiing Like the previous two, this family displays wide variations in abundance during the non-larviciding period (Fig 15). NeverEheless, no high densities were observed during the period of insecticide application, the numbers being practically zero in 1982 and 1983 whatever the preceding high water levels. It would seem that this group is greatly affected in the long-term by the insecticide applications, which would appear to confirm the high short-term susceptibility of Ehese insects (E1ouard, 1983). The following conclusions are reached for the Ephemeroptera as a whole: there seems to be a reduction in the Baetidae, certainly brought about by the chlorphoxim applications during the rainy season preceding the periods of falling water leve1s, when the abundance of this fanily is minimal. The alternation of insecticides could also have an influence on the abundance of t.his family: the populations of Caenidae are not affected either by the insecticides or by the alternation of insecticides; - the Tricorythidae must be severely affected, but in view of the small numbers collect.ed in 1976 and L977 this cannot be sEaEed with certainty. 3 . 3 .3 Ch ironomidae Danangoro station Whatever the insecticide applied, an increase in the total number of Chironomidae on the rocks is found by comparison with the number observed during the non-larviciding period(Fig. 16). The peak densities were observed in 1982 wtren the river was treated with B.t. H-14 following a chlorphoxim treatment campaign and in 1980 when the river was treated ilth temephos. Entomokro site The numbers of Chironomidae were always much higher during the period when the insecticides were applied than when they were not applied. These Eaxa may even be said to have proliferaEed during Ehe years 1980, 198I and 1982 (Fig. 17). Densities were lower in f983. This may be atEributed either to the hydrological conditions on the river (high water leve1 below normal) or to the discontinuaEion of insecticide applications. Moreover, it is Iikely that these factors produced a combined effect. We shall now aEEempE to present more specific resulE.s by studying the impact of insecticides on certain sub-families and tribes: the 0rthocladiinae, the Chironomini and the Tanytarsini. a ocP/vcu/HYBrol 84.4 Page 7 Or thoc 1 ad i inae The effect observed for this sub-family is roughly the same as that described for the Chironomidae as a whole: the density of these taxa was Sreater during the period when insecticides were applied, i.e. during the years 1980, 1981 and 1982 (Fig. 18)' The year 1983 was an exception; it should be borne in mind that the water level became excePEionally low and larviciding was suspended. The peak density of Orthocladiinae was observed in 1982 under treatment ritt S.t. H:14, following a larviciding campaign with chlorphoxim. Chironomini The density of this taxon was always much higher in the larviciding period than in the non-larviciding period (Fig. 19). The greatest abundance was observed in 1982. Tanyt ar s ini The effect produced on this Eaxonomic group by insecticide application is extremely spectacular. There is a very sharp increase in numbers for this taxon during the period of insecticide application, exclpt in 1983 wtrich was excepEional from a hydrological viewpoint(Fig. 20). The peak density of this taxon was observed in 1980 when temephos was used. The minimum densities, on the other hand, appeared after the chlorphoxim campaigns. The effect observed on the various groups of Chironomidae is therefore roughly the same as Ehat found for the farnily as a whole: application of insecticides is conducive Eo the multiplication of this taxon. It should be noted, however, that temePhos is conducive to the proliferation of Tanytarsini, whereas chlorphoxin seems to promot,e the prolifera_tion of 6rthocladiinae and Cirironomini, which confirms the results obtained with "broomstt(E1ouard, 1983; Lardeux, 1981). 3.3.4 Simuliidae During the period prior to larviciding there was wide variation from year to year in the density of Simulium species other than SimuliuT damnosum s.1. (Fig. 21). During the period of insecticide application the density of Simulium remained high, on average at least as high as before the start of larviciding. However, it is curious to note that the density was highest in 1982 wtren Ehe river was treated with B.t. H-14 and had just been subjected to treatment with chlorphoxim for several mcnths, and G-1983 when larviciding was suspended but the river had just been treated with chlorphoxim. The susceptibility of this group to these two insecticides is known (Dejoux et al., 1981; Dejoux et aI., it press). While in 1983 this phenomenon can be explained by rapid recolonization following the suspension of larviciding, it is more difficult to interpret it in 1982 wtren ttre river was treaEed with two insecticides that are effective against Simulium. However this may be, alternation does not seem to affect the density of the si-r-"ri"* species other than the onchocerciasis vector. 3.3.5 Pyralidae The results for this taxonomic group are difficult to interpret. Nevertheless, it may be observed Ehar (Fig. 22): - there was a wide variation from year t.o year in the density of this taxon during the larviciding period; chis fluctuation from year to year is also found during the larviciding period; it does not seem that the low densities observed in 1981 and 1983 can be attribut.ed to the impact of a given insecticide rather than to a particular sequence in the alternation of the insecticides used. ocP/vcu/HYBro/ 84 .4 Page 8 We conclude our consideraEion of this group by stating that if the insecticides have any action, it is not clearly distinguishable and can only be small. 4. COMPARISON OF THE RESULTS WITH THN SUSCEPTIBILITY OF THE TAXA As a result of many insecticide tests carried out both "in gutters in situ" and in the river, and monitored by means of the drift or the substrates, the I'sus".lEUifity"1 of the various taxa to certain insecticides, including chlorphoxim, temephos and B.t. H-14, has been established. The results obtained are as follows: Temephos The populations of Simulium damnosum s.1., the hydracarians, the Tricorythidae, the Philopotamidae and the Leptoceridae are greatly reduced by temephos. The Chironomidae, on the other hand, display littIe susceptibility to this insecticide. The taxa with moderate suscepcibility include the Hydropsychidae (Trichopt.era) the Caenidae, the Baetidae and Sirnulium species other than S. damnosum s.1. (E1ouard, 1983; Gibon & Troubat, 1982). Chlorphoxin. A11 the experiments show that this insecticide is much more toxic in the short-term than temephos for the non-target entomic fauna. In the operational dosages used in the Onchocerciasis Control Prograrmne it is difficult to establish precisely the susceptibility of the various taxa to this insecticide; they should all be included in thet'highly susceptiblerr category, except for the Orthocladiinae (Chironomidae) (Dejoux t Troubat, L976; Dejoux et aI., 1981, 1982; Gibon & Troubat, 1980', StaEzner, 1979). The Caenidae would also seem to be less susceptible to this pesticide than other insects. B.t. H-14. A11 the tests carried out show Ehat all Simulium species are greatly affecEl-by t.his poison. Other susceptible taxa are the Ortto"Lraiinae and Orthotrichia(Trichoptera: Hydroptilidae) (Oejoux, 1979; Dejoux et al., in press; Gibon et aI., 1980; Troubat et al., 1980). The other taxa are not affected by B.t. H-14. It should be pointed out that the results obtained from the monitoring of saxicolous fauna on the lower Maraou6 are partly confirmed by the short-term t'susceptibilities" of the organisms. Thus the proliferat.ion of the Chironomidae as a whole during the periods of treatmeot with insecticides, particularly temephos and chlorphoxim, is noE at all surprising since these are the least susceptible insects. It cannot be a coincidence that the maximum density of the Tanytarsini is found when temephos is used, while Ehe maximum density of Orthocladiinae is found during periods when chlorphoxim is used (figs 20 and 18). The fact that some t.axa reputed to be susceptible maintain their numbers or even proliferate after several larviciding cycles (with chlorphoxim, for example) is more surprising, as is the proliferation which occurs only in some years (e.g. Baecidae in 1980, Hydropsychidae in 1981 and 1982). In view of the susceptibility of Ehese taxa it would seem that if such proliferation is produced by the larviciding it can only be in a very indirect manner, a consequence of a disruption of insect conmunities and food chains. The authors believe that the river level, the time of appe arance and abundance of the Tristicha trifaria covering the rocks, and the insecticide applications conEribute just. as much to the developmenE of systems and to their variations from year to year. It must also be pointed out that all the results are expressed at family level, and thaE an increase in the density of one or more species may mask a decrease or even the disappearance of more suscePtible I Th" term susceptibility is used here in the broad sense and refers to the reaction of the populations vhen situated in their biotope. It would be preferable to talk of toxicity level in situ of an insecticide Eowards a taxon. Nevertheless, for the sake of convenience we shall continue to use the term susceptibility in the sense defined above. ocP/vcu/HYBro/ 84.4 Page 9 species or genera. Thus the verY high densities of Hydropsychidae observed in 1981 and 1982 while all the available data (Statzner & Gibon, inare due to the genus CheumatoPsyche, press) indicate that ;ince- larviciding began there has been a substantial regression of the distribution area and abundance of the Macronema tinae, particularly the gener a Macronema and ProEomacronema. This disappearance of the ttmajor predatorsrr can only be benefiffiffi-ftre species of the genus CheurnaqcptJehe. Although t,he initial utilizaEion of each o f the insecticides has in the short and med ium term produced ecological catastrophes at the Eaxonomic level selected, it would seem that these situations disappear fairly qu ickly after a year or less of successive applications. The African lotic environmenE seems Eo have fairly str resilience and at any r ate a grea! capacity for recovery. The fact remains that after four years of larvicidng on the lower Maraou6, using sometimes temephos, sometimes chlorphoxim and more rarely B.t. H-14, it cannot be said that the repeated insecticide applications have an effect on Ehe population densities for Ehe taxonomic groups as a whole (except the Chironomidae and the Baetidae). The natural variaEions in numbers observed during the years prior to larviciding are in each case of the same order of magnitude as those observed after larviciding. This does not mean Ehat there has been no impact, simply that the available data do not provide definite evidence of any impact. As reiards ttre'Cirironomidae it is quite clear that their densities increase suistantially wtratever insecticide is used. For the Baetidae and possibly for the Tricorythiaal it would seem that the use of insecticides, particularly chlorphoxim, is producing a gradual reduction in their numbers. Here again, however, Ehe wide flucEuaEions in the densiiy of these taxa wtrich were observed during the period prior to larviciding prevent any definite conclusion on this point. 5. CONCLUSION The alternation of insecticides as actised b oCP on Ehe lower I'laraou€ , does not appear to disrupt the taken in isolation. confidence that the s other insecticides. populations of aquat c1 nsects any more than In the light of the results, however, it cannot be ame would be true of other alternation sequences or of the insecticides stated with ' with the use of ocP/vcu/HYBlol 84.4 Page 10 REFERENCES Dejoux, c. (L979) Recherches pr6timinaires concernant lraction de Bacillus thuringiensis israelensis de Barjac sur la faune invert6br6e d'un cours dreau tropical. @721, 11 pp. Document Dejoux, C. & Troubat, J. J. (1976) Toxicit6 compar6e de deux insecticides organophosphor6s sur 1a faune aquatiq ue non cible, en milieu tropical. Rapp. ORSTOM Bouak6, No. 1, 60 pp. Dejoux, C., Gibon, F. 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Utilization of correspondence analysis for studying surveillance data c trop., 15(1), 23-3Lollected in the Onchocerciasis Cont,rol Progrartrne. Rev. Hydrobiol. Gibon, F. M. & Troubat, J.-J. (1980) Effets drun Eraitement au Chlorphoxim sur la d6rive des invert6br6s benthiques. Rapp. ORSTOM Bouak6, No. 37 , 12 pp. Gibon, F. M. & Troubat, J.-J. (1982) Effet du t6m6phos et du E6m€phos-sulfone sur les Invert6br€s aquatiques. I. Toxicitd compar6e du t6m6phos et du t6m6phos sulfone. Rapp. ORSTOM Bouak6 , No. 49, 14 pp. Gibon, F. M., Elouard, J.-M. & Troubat, J.-J. (f980) Action du Bacillus thuringiensis var. israelensis sur 1es InvertEbr6s aquatiques. I. Effet dr un traitement exp6rimental sur Ia Maraou€. Rapp. ORSTOM Bouak6, No. 38, 15 pp. Lardeux, F. (1981) Modification des structures de peuplement des Invert6br6s lotiques tropicaux provoqu6s par plusieurs cycles drdpandage drinsecticides antisimulidiens: t6m6phos et chlorphoxime. Rapp. ORSTOM Bouak6 , No. 45, 17 pp. Statzner, B. (1979) The effecEs of a large scale field application of Chlorphoxim on the benthic invertebrates in the Ntzi river (Ivory Coast). WTIO unpublished document, 72 pp. Statzner, B. & Gibon, F. M. (In press) A key to adult and inrnarure Macronematinae (Insecta: Trichoptera) in the Ivory Coast (West Africa) with notes on their taxonomy and distribution Troubat, J.-J., Gibon, F. M., Wongbe, A. I. & Bihoum, M. (1982) Acrion of Bacillus . rr. Effects offiffiiding onthuringiensis Berliner H-14 on aquatic invertebrates rhe drift cycle and the densities of benthic insects. Document llllO/VBC/... FIG. I. LOCATION ON THE RIVER MARAOUE OF THE TWO RESEARCH STATIONS SELECTED FOR THE MONITORING OF LOTIC ENVIRONMENTS TREATED WITH ANTI-BLACKFLY INSECTICIDES OCP/VCU/HYBIO / 84 .4 page 1 1 tstlUA Af,40 u ss0u:in0 LAC :rrSlatiorr ll CISSOU d-) 8 16 24Km PARC'Nt\f lCt,tAL ti .i,rr,.ittotiE il0Ul.A tl- -.:. -_;.' E OUIFL E .S.[:i ion I :, --atr--]: OCP/VCU/HYBIOI84.4 Page 12 c.) @ o\ l](d o >. 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