In its

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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.

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