Typology of susceptibilities of aquatic insect larvae to different larvicides in tropical environment

ONCHOCERCIASIS CONTROL PROGRAMME IN WEST AFRICA PROGRAMME DE LUTTE CONTRE L'ONCHOCERCOSE EN AFRIQUE DE L'OUEST Enüronmental Monitoring Service Service de Surveillance de l'Environnement Technical Report ocP/vcu IEMS/e0.3 Typolory of susceptibilities of aquatic insect larvae to different larvicides in a tropical enüronment Rf,P 7, ?. §. TYPOLOGY OF SUSCEPTIBILITIES OF AQUATC INSECT I-ARVAE TO DIFFERENT LARVICIDES IN A TROPICAL ENVIRONMENT L. Yaméogo*, J.-M. Elouard** and M. Simier** *Onchocerciasis Control Programme, 01 B.P. 549, Ouagadougou 0L, Burkina Faso **ORSTOM 2051 Avenue du Val Montferrant 34032 Montpellier, Cedex, France 2ABSTRACT Multi-gutter tests are used by the Onchocerciasis Control Programme in West Africa to screen antiblackfly larvicides with reference to non-target aquatic insect larvae. Because the tests are not always conducted under the same environmental conditions, direct comparison of results by the usual methods of data analysis presents some difficulties. The application of reciprocal averaging (correspondence analysis) to data from tests carried out using the same protocol indicates that the test periods have no incidence on the impact in gutter of the larvicides. The analysis also makes it possible to classiÿ the insecticide families according to their degree of general toxicity on fauna. In addition there is no evidence of a uniform effect produced by each insecticide family on the principal taxa. Keywords: Antiblackfly, Reciprocal averaging analysis, Multi-gutters, Benthic fauna, Insects, Typology. 3I. INTRODUCTION Human onchocerciasis is a filarial disease which constituted, a serious public health problem and an obstacle to the socioeconomic development of the fertile valleys in many parts of West Africa. The disease is caused by a filarial worm Onchocerca volvulus. It is transmitted to man in West Africa by the female of a small fly (the blackfly) Simulium damnosum complex (Philippon, L977). The worm can cause serious skin and eye lesions which eventually lead to blindness of those affected. To fight against this disease, the Onchocerciasis Control Programme (OCP) was launched in L974 by WHO together with UNDP, FAO and the World Bank. The strategy adopted was the use of larvicides against the aquatic stages of the vector, since no safe drug for mass treatment was available. Because of the short larval life span of the blackfly, the larviciding was done weekly in fast-flowing river stretches where the vectors' larvae developed. For many years temephos, an organophosphorus insecticide, in a 20Vo emulsifiable concentrate formulation, was the only product used until the appearance in 1980 of resistance to it (Guillet et al., 1980). By 1982 resistance to chlorphoxim (another organophosphorus compound) had also developed in certain forest cytotypes of the vector (Kurtak et al., 1982). These findings led to the acceleration of a screening programme in a search for possible alternative larvicides. The selection of insecticides is based mainly on their efficacy against the vector (Kurtak, 1986) but also on their toxicity as regards the non-target fauna 4(Yaméogo et al., 1988, Lévêque, 1989). More than some sixty products from different chemical families have been tested but less than half of these larvicides have been the subject of studies on the non-target fauna, particularly insects. Among the different techniques for studying the short-term impact of larvicides on non-target benthic fauna, that of gutters (Dejoux, 1975 and 1980; Troubat, 1981; Yaméogo, 1984) is usually employed. However, the general comparison of test results has proved difficult just as the general estimation of the toxicity of the chemicals. Two major reasons account for these difficulties. First, the environmental conditions under which tests are conducted vary considerably from one experiment to another. Secondly, there is a specific susceptibility of the taxa to different insecticides. Besides, from a theoretical and maybe a predictive point of view, it will also be interesting to know whether products belonging to the same chemical family (organophosphorus, carbamates, organochlorine and pyrethroid, growth regulator compounds, bio-insecticides, etc.) have the same toxicity for the same taxa. All these tests, carried out on the non-target fauna as part of the selection of larvicides, have therefore been analysed and the main results are discussed in this document. il. MATERIALS AND METHODS The results, presented and discussed in this paper were obtained during tests conducted using the technique of multi-gutters (Troubat, 198L). A gutter is a plastic 5experimental apparatus modelled to represent a reduced stretch of river (Fig.1) with, at one end, a stop net for natural drift and, at the other end, a net for collection of drift of organisms taken from the river with the substrates (stones, sand, dead leaves and wood, etc.) to colonize the gutter. The system is installed in rapid zones of a river which is not very deep, in such a way that the water runs right through them, the water level reaching about half of their section. Drums containing the pesticide solutions to be tested can be placed at the upstream end of the gutters. Thus, different concentrations of a given pesticide or different pesticides can be tested simultaneously while maintaining a control gutter. Drifting fauna is sampled periodically (every 30 min. for 4 hours, then every hour for 20 hours) for a24-hr period. Then, the remaining organisms in the gutters are collected separately, fixed in alcohol and labelled (as all the other samples) to be studied in laboratory. It is therefore possible to compare the impact of different larvicides or different concentrations of a larvicide using the detached organisms or those remaining in the gutters. The organisms used in the different tests were identified to the family level for all the aquatic insects with the exception of the Chironomidae which were separated to the subfamily or tribe level. Furthermore, only the ta;ra presenting a wide geographic distribution and which were relatively abundant in almost all the tests have been taken into account. 6The perceîtage of detachment of the organisms in the gutters, considered as a percentage of mortality after correction by the Abbott formula (Finney, 1962) taking the natural mortality in the control gutter into consideration, is the value indicating the toxicity level of the larvicides. Reciprocal averaging analysis (correspondence analysis) were applied to these corrected data by using the "BIOMECO" programme of the Biometrics Group of CEPE-CNRS, Montpellier (France). This method of analysis, introduced by Foucart (1978) and Benzecri (Benzecri &Berzecri, 1986), possesses a good descriptive power as regards tables of positive numbers (without these being tables of probabilities or frequencies). It should also allow a good description of the long-term effects on non-target aquatic insects of the use of pesticides against blackflies (Elouard & Jestin, L982; Elouard & Fairhurst, L990; Fairhurst & Curtis, 1988) and of the biotypology of running waters (Culp & Davies, 1980; Dakki, 1985). The insecticides tested, the dose as well as the dates and places (localities) of the tests are given in Table I. Among these larvicides, temephos, chlorphoxim, carbosulfan, permethrin and pyraclofos are used operationally by the Onchocerciasis Control Programme. To answer the different questions raised in the introduction, the analyses covered, firstly, the fauna that colonized the gutters before treatment (tested fauna) and then the fauna that remained in the gutters 24 hours after the larviciding was taken into consideration. 7III. RESULTS AND DISCUSSIONS. 1. Tÿpolory of the tested fauna Analysis of the basic communities that colonized the gutters before treatment and tested using the same protocol at different periods of the year is illustrated in Figure 2. The examination of this factorial plane 1. x 2, whose first a:ris (F1) explains 44Vo of the variance (inertia) out of a total of 79%o for the plane, calls for two remarks: - the F1 axis is based on the contrast of the flood-subsidence structure of macroinvertebrate communities at Koperagui (October), influenced by the Tricorythidae, with the others (Amou-Oblo and spate period at Koperagui); - as regards the second axis (F2), it contrasts the spate period at Koperagui (July-August), influenced by the Tanytarsini and Hydropsychidae, with that of the flood-subsidence at Koperagui and the rise in water level at Amou-Oblo influenced by the other ta:<a with the exception of the Tanypodinae which did not contribute much to this axis. The typologies described above are therefore related mainly to the hydrological seasons. 2. Tÿpologr of remaining fauna (in gutter) The remaining fauna is that which has escaped from the impact of the larvicides. A comparison of the community structures obtained in this way with the basic ones of the gutters, will make it possible to understand eventual modifications caused by the insecticides. Besides, the ÿpologies of the remaining fauna should be 8quite close to those of the saxicolous fauna of the watercourses treated with the antiblackfly larvicides; the gutter being considered as a miniature watercourse. The objective of this study is to correlate the short-term toxicity of larvicides in gutter systems with community structures in treated rivers and,later on to establish a model for forecasting the long-term impact of the larvicides on the sa:ricolous fauna on the basis of their short-term toxicity. Analysis of the typology of the remaining fauna in the gutters seems therefore to be more appropriate than that of the mortality in gutters. As seen earlier, the ÿpologies of the fauna in place in the gutters before treatment are related to the hydrological seasons (Fig.z). A correspondence analysis has been made for the fauna remaining in these same gutters 24 hours after treatment (Fig.3). This factorial plane L x 2 explairs 61.%o of the inertia. The first axis contrasts the Chironomidae, which are characteristic of the gutters treated with the relatively toxic insecticides (carbosulfan, pyrethroids and chlorphoxim), with the Ephemeroptera which are associated with the most selective doses or larvicides. The second a:ris contrasts the Chironomini and Orthocladiinae with the Tanytarsini and Tanypodinae. It reflects, therefore, the selectivity of the products as regards the Chironomidae while the F1 axis classifies the larvicides according to their general toxicity to the fauna as a whole. It will be noted that the Hydropsychidae, which present a medium susceptibility to most of the larvicides (Table II), do not contribute much to the a,xes. 9The typologies revealed seem to be stable and do not depend on the basic structure of the gutter communities. They suggest that taxa that are not much affected by an insecticide should remain in the watercourses treated with it, while the population of the susceptible tana would decrease. However, the complexity of the biological phenomena calls for caution because the immediate impact observed during an isolated treatment could be affected in the long run by factors such as trophic and spatial competition, habituation or resistance or other forms of adaptation, the duration of the larval development cycles, etc. IV. CONCLUSIONS The correspondence analyses applied to the multi-gutter test data show that the impact of the larvicides is greater than the effect of the test period. Besides, although this type of analysis is solely descriptive, it gives a good idea of the toxicity of the larvicides on the main components of the biotic enüronment. The ÿpologies recorded for the fauna remaining in the gutters contrast the selective insecticides, which are associated with the Ephemeroptera (susceptible organisms), with the relatively toxic insecticides associated with the ubiquitous organisms. These typologies do not depend on the insecticide family because some of the pyrethroids present a greater toxicity to the Chironomini (ryphenothrin), and others to the Tanypodinae or the Tanytarsini (deltamethrin, ethofenprox). On the other hand, a certain 10 classification of the toxicities of the products according to insecticide families is observed. Thus, generally speaking, the organophosphorus compounds are less toxic than the pyrethroids which are effective against the onchocerciasis vector. Finally, the typologies revealed in this way and analysed, taking into account those established after the long-term use of pesticides in lotic environments (Elouard et al., 1990), should make it possible to develop a model for the prediction of the long-term impact of the larvicides. ACKNOWLEDGEMENTS This work, financed entirely by WHO/OCP, was carried out in the field with the technical collaboration of the staff of the OCP Environmental Monitoring Unit (particularly Mr B. Coulibaly and Mr M. Bihoum) and consultants, including Mr B. Wahle, to whom we are grateful. 11 Bibliography BENZÉCRI (J.P.) et BENZÉCRI (F.), 1986. Pratique de l'analyse de données. Economie, Dunod, 533p. CULP (J.M.) & DAVIES (R.W.), L980. Reciprocal averaging and polar ordination as techniques for arralyzinglotic macroinvertebrate communities. Can. J. Fish. Ag. Sci., 39, 1258-1266. DAKKI (M.), 1985. Sur le choix des données en biotypologie des eaux courantes par l'analyse factorielle des correspondances. Bull. 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Doc. 0765|VCU (1984) WHO, Onchocerciasis Control Programme, Ouagadougou, 26 p- YAMÉOGO (L.), LÉVEQUE (C), TRAORE (K) et FAIRHURST (C.P.), 1988. Dix ans de surveillance de la faune aquatique des riüères d'Afrique de l'Ouest traitées contre les simulies (Diptera : Simuliidae) agents vecteurs de l'Onchocercose humaine. Naturaliste can. (Rev. Ecol. Syst.), l1'5 :287- 298. t4 TITLES AND LEGEND OF THE FIGURES Figure 1: Diagram of nvo rypes of gutter (simple A and multiple B) used in situ for the study of the impact of insecticides on benthic fauna. Figure 2: Typotory of fauna in place in gutters during tests conducted under different conditions LEGEND Bae Baetidae SPate at KoPeragui Tri Tricorythidae Chi Chironomini Flood-subsidence at Koperagui Tat Tanytarsini Tap Tanypodinae Ocl Orthocladiinae Psy Hydropsychidae Cae Caedinae Beginning of rise in water level at Amou-Oblo Figure 3: LEGEND Typology of fauna remaining in multi-gutters after the action of different insecticides tested by OCP, using the same protocol Az Azamethifos Bio Bioresmethrin CarbosulfanCa C} Permethrin 15 Cy Qphenothrin De Deltamethrin Etf Ethofenprox 02 oMS 3002 04 oMS 3034 06 oMS 3036 ry Srraclofos Ph Chlorphoxim Ta Talstar Te Temephos T * Srrethroids Carbamates Organophosphorus compoundsA t6 Table I : Insccticidcs tcsted in multiPle-guttcrs on thc non-targct aquatic fauna INSECTICIDE NAME DOSE (ppm/10 min.) INSECTICIDE FAMILY DATE PI-{CE NUMBER OF ORGANISMS TESTED Cyphenothrin Cyphenothrin oMS 3034 Permcthrin (Coopcx) oMS 3036 Temephos Control 0.05 0.01 0.02 0.015 0.3 0.1 $rethroid Pyrethroid Brrethroid Pyrcthroid Pycthroid Organophosphorus s/t0lî36 Kopcragui (Côtc d'Ivoirc) 2733 3f.22 4750 2589 4052 3t97 4203 Temephos Carbosulfan Carbosulfan Ethofcnpox Biphenthrin Cfalstar) Permethrin (Coopcx) Permethrin (Coopcx) oMS 3034 Cyphcnothrin Control 0.01 0.05 0.075 0.1 0.01 0.015 0.02 0.02 0.01 Organophosphorus Carbamatc C:rbamatc Pyrethroid Pyrcthroid Brrcthroid Pyrcthroid Pyrcthroid Pyrethroid t3lL0/K Kopcragui 258/. 2606 2'789 28% 2720 UM 3605 3592 2û3 21,45 17 INSECTICIDE NAME DOSE (ppm/l0 min.) INSECTICIDE FAMILY DATE PLd\CE NUMBER OF ORGANISMS TESTED Pyraclofos Pyraclofos Pyraclofos Pyraclofos Chlorphoxim Chlorphoxim Temephos Temephos Control 0.05 0.1 0.2 0.3 0.05 0.1 0.05 0.1 Organophosphorus Organophosphorus Organophosphorus Organophosphorus Organophosphorus Organophosphorus Organophosphorus Organophorphorus 7/71§ Kopcragui 1332 1475 LÆ2 IM 93L 727 2696 1816 1826 Temephos Deltamethrin A Deltamcthrin B Control 0.1 0.0005 0.0005 Organophosphorus Ilrrethroid IlEcthroid 2U6183 Amou-Oblo (fogo) 556 614 629 1004 Temephos oMs 3002 Azamethiphos Control 0.05 0.2 0.2 Organophorphorus Bnethroid Organophosphorus Le/s/83 Amou-Oblo 1.574 2235 820 91,6 Control Bioresmethrin Broresmethrin Bioresmethrin 0.00625 0.0125 0.05 Pyrethroid Pyrcthroid Pyrcthroid 2618188 Kopcragui 8763 2385 3967 4tt4 o §, .oH oë 6 + ++++++ +++++++++++++ ++++++++++++++ o6E Éo6(J +++++ +++++++++++ ++++++++++++ ++++++++++++++ o «,E o À o E >. + ++++++++++ ++++++++++++++ o6É E6tE E ++ +++++++++++ ++++++++++++++ É ec É -6F + +++ +++++++ ++++++++++++++ o6 .EI *É .GF ++ +++++++++ ++++++++++++++ É oÉ o ÉU + ++ +++++++ ++++++++++++++ o6p o A +++++++++++ ++++++++++++ +++++++++++++ ++++++++++++++ o(, P Ëoo :EF +++ ++++++++ ++++++++++ ++++++++++++++ 6x6tj oo a Io É I aE Ë E.E YE E x Êâ˧saËEâg§EEË @ Fl o o aàorx 7,P,ô;-q9.àÉ8EEOr='i=Eîi ifi'ÉEEâ3- :Ë FE ÉÉE E .95:??ȧ§F' -ooi oO\OcO\:/ :gE6x§E§ E EHià638Ê91 G «)lOOË:ËËË -?ooYÈ,:4.ô.ot9- ,.Yoooo =EEEEEgttE 9AOaA6G§§ ooooL' =HHH5 ô.o++8+++A++++ Ei g o6F