Effect of bactimos on aquatic invertebrates: effets of release on benthic insect densities

DI t t I'IINISTRY OT NATIONAL EDUCATION AND SCIENTIFIC RESEARCH INSTITUTE. OF TROPICAL ECOLOGY ITE/WHO AGREEI.IENT MONTToRTNG THE AQUATTC ENVTRONI{ENT EFFECT OF BACTIUOS ON AQUATIC INVERTEBRATES. EFFECTS OF RELEASE ON BENTI{IC INSECT DENSITIES TI.A. YTE Fieh-reering 'Centre/ Idessa P.O.Box 695, BOUAIG 01. INTRODUCTION In its constant preoccupation with the search for more effective insecticidea or Larvicides, the Onchocerdiaeis Control Programne (lfilO) tests out new producte daily. This lras the context in which one insecticide, Bactimos wae tried out on 7 Decenber 1983 in the Saesandra (Senian) We were asked to maasure the iurediate impaet of thie product on the deneity of the aquatic invertebretes of the environment. The results obtained are set out in the preeent report. I. LOCATION OF TIIE STUDY'ZONE A}ID INFORI,TATION ON INSEqTICIDE RELEASE Thia study lras carried out on 7 Decenber 1983 in the Semien breeding eite eituated on the Saesandra 70 kil.oqetree froo man and roughly the aane distance from S6guela-Man main road. The releaee, which was cerried out froq the air took place between O7.OO and 13.3O. The ineecticide enployed rilas e fornulation based On Bactiobs in,a coneentrated euepenaion. Hydrologicel conditiona were ebnormal owing to the lack of rain duping the year throughout the territory. The abnoruelity showed iteetf iq the field in a Light epate eituation (0.9 mleee).and raiaed deneitiee of the benthic fauna. II. RESEARCH METHODS A direct approach wae adopted: uce of the Surber sampler to etudy the population of rock elabs, A Surber eanpler was ueed to take ten 0.0225 m2 aamplee before treatment and another ten after. In as far as possible the sanples lrere paired so as to take theo under the same conditione of flow rate (0.9 o/sec on average) and devel.opment of the vegetation. III. RESULTS AND DISCUSSION The benthic fauna is dorniqated by two groups, Chironomidae (nainly Chironomini and Orthocladiinae), Simuliidae and sizable populations of PyraLidae and Oligochaeta, as well ae Ephemeroptera (nainly Baetidae). WORLD HEALTH ORGANIZATION ORGANISATION MONDTALE DE LA SANTE ocP/vcu/HYBro/84. 16 ORIGINAL: TRENCH Co docrrment ne congitue pas une publicrtion. ll ne doit faire l'obiet d'aucun compte rendu ou rdsumd ni d'aucune citation eans l'autorisation de l'Organirotion mondiale de la Sant6. Lcs opinions exprimdes dans les articlca rign6s ntngagent que leurs auteurs. a The issue of this document dges not constitute formal publication, lt should not bo reviewed, abrtracted or quotod without thc agrromGnt of the World Health Organization. Authors alonc are responeible for views expreesed in dgned articles. ocP/vcu/HYBro/ 84. 1 6 Page 2 The reLative importance of Lepidoptera (Pyralidae) is explicable by the development of vegetation (Tristichia trifaria). This situation is a little special by cornparison with other years in which it was impossible to study the benthic fauna of the rock slabs at the same period owing to the spate. It is therefore difficult for us to conclude wtrether or not this populaEion composition is unusual for the site and could be connected with the hydrological situation. Overall density was high; the mean of the 10 samples taken before Ereatment was 281925 \ organisms per square metre The special lorrwater situation accompanied by a concentration of larvae in the last t favourable biotopes would explain this high density. Furthermore, the densities appear uniform, the calculated standard deviations are slight and clearly below average (Tables 1 and 2). We used Studentrs test to etudy the effect of treatment on the best represented taxa. The test was positive at 0.05 for Sinuliidae, Oligochaeta and Tanytarsini (Chironomidae). It lras negative for Hydropsychidae, Leptoceridae, Chironomini, Orthocladiinae and Pyralidae. Consequently, we have established that treatment had an effect only for the Simuliidae, Ehe average numbers of which fell fro,rn 61613 to 4rO0O per square metre after treatment. The insecticide employed would not appear to have any effect on Chironomini, Orthocladiinae, Leptoceridae, Baetidae and Pyralidae. The densities of the other taxa noted rrere too low for any conclusion. The Eaxa concerned were Heptagenidae and Tricorythidae (Ephqneroptera), Hydropsychidae and Tanypodiinae. CONCLUSION The lack of infornation on the drift index prevents us from the outset from eslablishing a comparison with the toxicity of other insecticides al.ready invesEigated. Even eo, direct analysis of the effects of our treatneot on the densities of the principal taxa does demonstrate.the harpleseness of this produce, for Baetidae, Chironomini and Orthocladiinae (Chirononidae), Leptoqeridae (Trychoptera) and Pyralidae, the taxa that together with Simuliidae and Ol.igochaeta, constituted the bulk of the benthic fauna at the tirne of thege experiments. This result would therefore seem to be somewhat akin to the results obtained with Bacillus thuringiensis Berliner H.14 (Troubat et al, 1982; YTE, 1982). Other experiuents woutd enable this effect to be better eetablished. ocP/vcu/BYBro/ 84. 16 page 3 REFERENCES Dejoux, C. (1979) Recherches pr6liminaires concernant t'action de Bacillgs Thuringiensis isia1ensisdeBarjacsur1afauned|invertebr6sd|uncoursd|eautil ffi-oFbc-79-721, 11p. Gibon,F.M.,E1ouard,J.M.,Troubat,J.J.,(198o).Actiond,@'... isralensis sur les invert6br6s aquatiques: Effets drun traitement exp6rimental sur la Marahoud. Repp. Lab. Hydrobiol., Bouak€, 38, 11 p. nultigr. Troubat, J. J., Gibon, Thuringiensis Ber liner Cycle de d6rive et Les 48, 8 p. multigr. F.!,I., Yte, W.A., Bihoum, M., (L982)... Action du Bacillus H-14 sur 1es invert6br6s aquatiques. II. Effets drun {Pandage sur le densit6s drinsectes benthiques. Rapport. Labo, tlydrobiol. Bouak6, yte, W A. (1982) Action du Chlorphoxim sur Ies invertebr6s aquatiques. Effets drun Epandage sur 1e cycle de d6rive et les densit6s dtinsectes benthigues. Rapport I.E.T. Abidjan, 1' 4 p, multigr. o\ lr N z OO o\ LO\o O!O \o a# rd +J Er -t .J-l-\ CO N CO - ca a-l cO \O \a (aO N \O O \.o La O O O O F$ !a O ci chrO- Or fa - cO O oo -.:1.F- N O OOO O OOOOO-, -e{ caetOOO O OO\OOOGl e\l Gt F\cO 0O (n@ \O -o.l N sl - Or-$ O cf)@Or6-.$ O\ CO rn6.l O - ro - - \() O cO ca O O O O O - c.l Or cc) cO cO ci O -a - O C) O -1- O.lF--- N $rn-cf) \t cn cO O cO Ln Lo O - O O O N - @ O O@ cO O -).f, - O O :. 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