re ort

Gunnar C rlss n

Benthonic F una

in African Wa ercour es with Speci 1 R feren e to Black Fl Po atio

ese

re ort

Gunnar Carlsson

BENTHONIC FAUNA IN AFRICAN WATERCOURSES, WITH SPECIAL REFERENCE TO BLACK-FLY POPULATIONS.

Seandinavian e of Studies

WITH SPECIAL REFERENCE TO BLACK-FLY POPULATIONS

By Gunnar Carlsson

INTRODUCTION

During July ^QYlr1 1\1.1gust 1965 and 1966 investigations were carried out in watercourses in diff~rent ~arts of Africa, in order to test a methodology for studying the environmental factors of importance for the larvae of the vectors of onchccerciasis, the black-fly species Simulium damnosum (s.L,) and So neavei (s.,L). These Simuliidae are

carriers-'o~rthe~-filarialworm OnDh-åcerca volvulus, the cause of onchocerciasis, a disease which'is of great importance in many parts of Afrioa and Central America, where blindness due to onohocerciasis affliots about 30 million of the inhabitants. The field investigations covered large rivers and small rivulets in different vegetation zones, from tropical rain forest to semi-desert. A special technique was used to rear parasites and to fix black-fly larvae for karyological mappings. The investigations and conclusions are described below, with the exception of the cytological observations.

lflATERIAL

Dv~ing 1965 data were obtained from localities A - J in West Africa and localities K - R in East Africa were visited during 1966

Investigations, especially on black-fly larvae, were carried out in small stres1llS and ri vulets in the of the ^Ilmain locali ties"

A -

The columns hended iJBedrock^fi and 1130il ll give the predominant kinds at the investigation locality and upstre8.lll; the IICurrent velocityll

column gives the mean value of measurements at many representative spots on the watercourse; the number given in the IILake" column shows the distance in km to the nearest lake or large pool upstream;

+ in the liV/ater levelII column indicates a water level above the mean level and - a water level below the mean levelon the occasion of the

investigation.

TABLE I l.ocal ity

A. Barombi lake, 5kn N. KunDa, CalOOnJon

Altituda, Badrock ma.s.l.

250 Volcanic

Soil 'Iidth, Invest.

m depth,

m

La te- 4-8 0-0.7

rites

Current Substratum ve10city,

m/s

0.8 Stones, grass

lp1'9 \'Ie ter level

o

⁺

La te- 4-10 0-0.8

ritas

Lata- 100-170 0..0. 8 rites

La ta- 5·7 0-0.5

ritas 210 Volcanic

+

+

+

+ (+)

12 +

30 +

20

No +

No

No

No

No Iiud , stones

(si11:';), grass Stones, rocks 0.7 Stones,

gravel, plants 0.6 Stones,

rocks, plants 0.3

0.7

0.8 Stones, gravel, plants 0.3 Stones,

gravel, plants

0.2 liud, p18nts, O +

sand 0.4 Stones,

(silty) mud 0.2 ijud, sub-

mergoo plants

o.

^{3-J~1 Stonas,}

gravel

0.2 t'lud$ sub- Pools +

IOOI1JOO 1

plants 0-0.8

0-0.7

0-0.7 0-0.6

0-0. l 0-0.4 0-0.4 J·3

5-12

J-4

3-7

7-16 80-100

]. S-3

o.S-1.5 Pnasrhatas, Late-

eoceni c ritas, s\olamps

Grani tes lata- di orites rites Phosrnatas, late- eoceni c ritas

COrYJ1orne- Chemo- rates & zems &

sandstones clay COt)j10100- Ch emo-

rates zem

COt)jJorne- Chamo- rates & zems sandstones

Crysta11 ine Lat e- racks, pre- ri tes cambrian

Crysta 11 ina Late- rocks, pre- ri tes cambrian

200 Grani tes

100

500 JOO

150 Grani tas

350

330

310 B. Barombi lake,

12 kmdownstream

C. 1'lut)jo river, 21 knilE. I<umba

D.Tri butary to C, 5kmN. i'lbat)ja E. Ogun river, 20 kmtf. Lagas, Nigeria F. Shasha river, 20km Ni/. Lagas.

SWOO1PSaround G. Pa~71pawn rlver, 2kn S. Hohunya, Ghana

Kl' SmaJl rivu1et, 850 tri butary to 1<

H. Seasona l stream, 30km_~E. Bama ko, Ha11

\. Seasonal stream, 22 kmilE. Oamako

J. River, 15 km Sid. Bamako, t'la li

K. Streamroar Amani, 850 Tanzania

LocalitJ Altituds Badrock Soil Ilidth, I!West. Current Substratum Lake Hatar

m,a.s,l. m depth, velocity, lavel

m m/s

L. l(agera river, 1,250 Cong1000- ? 20-200 0..0.5 1.1 Stones, 50 +

8 I® E. Ki kagati , r'ates rocks

Uganoo

N. NYamagasami, ~O Gran ites, Clay, 4-8 0..0.3 0.9 Stones, No ?

stream in southern gneissas, moraina gross

Ru>KlnZori e.mphibo1itas

N. Nubuku ri ver, 2,900 Grani tes, r'loraine 5·20 0..0.5 0.9 Stones, ?

eastern Ruwenzori gneisses, gravel

amphiboJi tes

O. telubuku river, 1, JOO Granites, CJay, 8·20 0..0.5 1.2 Stones, No ?

Fort Edward gneisses, moraina grass

amrhi boli tes

P. Tributary to 2,700 Grani tes, Moraire 4-JO 0..0.3 J.3 Stones No ?

r'lubuku gnei sses,

amphi bol ites

U. RivuJet near 2,600 Granites, f'loraira 0.2-1 0..0.1 0.3 Stones, No ?

rlubuku grai sses, grave1

amphibolites

R. Itojo ri ver, J,2oo Grani tes, Sand, 2~6 0..0.3 0.7 Stones, No ?

25 I®MI. Fort gneisses, clay, gravel

Portal, Uganda amphiboli tes moraine

I:TETRODS

On visiting a locality, the data shown in Table 2 were obtained& For karyological purposes, some larvae with black histoblasts were fixed in the field in a modified Carnoy solution. Processing (cytology) was carried out according to the standard procedure, described by Rothfels (1956) and Basrur (1957). For detailed morphological analyses the different characters of the larvae were prepared and put on slides.

For one snd the same specimen both the cytology and the morphology were studied and thus direct comparisons could be made. For rearing parasites, especially Mermithids, some 1arvae were kept alive in tubes as long as possible, to allow the parasites to develop through a few stages or to escape from the dying larva. The material was then put inta a solution of 80% ethanol, l~/o glycerol and 1% methyl blue.

TABLE II. Physical and cnemical factors

The number given under "Pollution" shows the actual degree: 0= none, 1= insignificant, 2= noticeable,

3=

heavy and 4= very heavy pollution.

Locallty Date Hrur Temperature pH Cl

-

_CaO

Oz% Pol1ution I'leather

Air \'!ater mg/l mg/l Sa tur.

A1965 13/8 8-11 25.5 27.5 6.7 2.7 15 80.4 Clou:ly,

6U!

cumu1us

B 13/8 14-17 28. O !I.2 6.7 3.0 20 89.5 Clou:ly, 5m cumulus

C 14/8 9-12 31.2 24.0 6.1 2.7 30 89. 9 O C10lrly, 5~ cumu lus

D 14/8 15-18 33.2 27.2 6.5 13 30 947 2 C10lrly, 6O'Zcumu lus

E 16/8 11-14 31.2 !I.2 6.4 10 24 le.O 2 Fine, 3ql; cumulus

F 17/8 13-16 28.5 25.8 5,5 9 15 21.5 Heavy rain

G 19/8 13-15 25.7 24.2 6.2 19 20 94.3 Clou:ly, 7~ cumulus

H 22/8 11-14 28.5 33.2 5.7 3.4 28 93.4 1 Fine, thunder at a distance

I 22/8 16-18 26.4 30.1 2 Clotr!y, thunder nearby

J 23/8 9-12 24.5 26. O 7.0 20 35 86. 1 2 C10lrly, 1~nimbustratus

K1966 26/7 14-16 20.0 18.7 6.8 11 17 90..0 O C10udYl 6l1oCumulus

1(1 26/7 14-17 20, O 18.2 6.9 O Cloudy, 6O'Zcumulus

L 30/7 1Q..13 26. O 21.2 6.9 5.9 35 91. O l Fine

N 30/7 17-19 26. O 19..5 1 C10lrly, 1~

N 31/7 15-17 17.9 9.5 6.6 O C10lrly, 1~

O 1/8 9-12 20.8 16.2 6.7 2.5 35 92.0 1 CIOlrly, 1~

p _{31/7 c. 18 17.0 13.0 O Clot.rly , 1~}

Q 31/7 c. 19 'IB.5 14.0 O C10lrly^I darkeni ng

R 1/8 16-19 2¹+.0 22.3 7.8 3.9 101 c. 70 81ot.rly^I 1~

TABLE III. Record of field investigation.

LOCALITY: Barombi lake, outIet, 5 km N. of Kumba, Cameroon Altitude: c. 250 m.

Bedrock: valeanie, upstre8m: volcanic.

Quaternary deposit: laterites; upstream: laterites.

T}ill STREAM: Width: 4-8 m; investigated depth: 0-0.7 m; current velocity: mainly 0.8 m/s

Substratum: stones, submerged grass and plants. Same timber logs.

Silt on stones.

Lake: i~nediately upstream. Auxotrophy: none noticeable Same fishing.

FLORA: In the stream: very poor, same mosses only Around the stream: tropical rain forest, very dense

FAUNA: In the stream per 1,000 cm2 of representative bottam substrata:

Date ex;^o Water Ephem. Plec. Trich. Chiron. Simul. Others Total hour level No. VIft No.

wt

No. wt No. Vit llJo. wt No.

wt

No. wt

13/8 + ² 5 ^{12 20 12} 7 2 5 3^{a 125} 31 402

8-11

a Including two large Odonata larvae.

Simuliidae: larvae and pupae present: 36 larvae from 20,000 cm •2 Four S. kcnyae (4-6 stages, l with Mermitidae); 32 S. damnosum (4-6 stages, mainly 5-6, 4 with Microsporidae); 2 IIfreshll pupae.

Remarks on egg masses: none observed (cf. black flies).

Parasites: 50 pupae + 40 larvae for rearing parasites.

Karyology: 40 larvae in Carnoy solution. Salivary glands extruded.

Around the stream: c. 20 black flies at the same time around the legs, usually not more than l m above the ground. Some bites to a small extent. No black flies on the plants around the stream. Lots of black flies at twilight and more intensive bites. Of 55 investigated

fem8~es of S. damnosum, all Were nulliparous, none had nematodes in the midgut, in the thoracic nmscles or on the mouth-parts. At least 8 with Wticrosporidae in the ovaries. Seven were newly emerged. Other insects around were Strepsiptera, Ephemeroptera, Trichoptera, and Diptera of many kinds. Same spiders.

ORGANIC DRIFT:

Net of plankton Date Phy Zoo hour

13/8 8-10

gauze Paddle-wheel apparatus

Det Ino T p T a 'IV 8. A a Inorg. Total ml/m3

:;{ _l ~d 1 l l l 4

a Mainly diatoms and Chlorophyceae. b Crustacae and Rotatoria.

c Lots of chitinous fragments. d Mainly leaves.

PI-IYSICAL AND CHEIlIIOAL FAGTORS:

Date Temperature _pH 01

-

_{CaO O}

_%

_Weather

Air Water mg/l mg/l satur.

13/8 25.5 27.5 6.7 2.7 15 80.4· Cloudy, 60% cumulus 8-11

GENERAL REMARKS: Very high water. Compared with European and North American conditions a very poor bottom fauna (outlets usually highly favourable localities for rheobionts and rheophilous organisms, mainly because of a rioh and oomprehensive organio drift). Suggestions:

nulliparous females only beoause they were newly emerged; no masses of black-fly larvae beoause of laok of suitable substrata (stones usually with silt); the meoh8nioal effect of the high water oauses drifting away; the organic drift of bottom-dwelling organisms low beoause of the hour (at dawn and sunset more intensive drift is to be expeoted); relatively few parasites, which might have been due to low population density and olear no traces of egg development in the ovaries whioh might mean anautogeny.

Generally speaking the values found are comparable with those found in southern Seandinavia and in watereourses around the great lakes in North America, which are not auxotrophied. The most remarkable value in Table II is 101 for CaO at loeality R and consequently high pH (7.S). There is no human pollution upstream, so it might have been due to the loeal limestone bedroek around the stream. The low oxygen saturation, 21.5%, at loeality F is erplained by the faet that the stream runs through large swamps, where oxygen consumption is high.

ORGANIC DRIFT

The continuous drift of benthonic organisms in running water has been studied previously (Carlsson 1962, MUller 1966). The following faets are known about this organie drift:

l. The drift is maintained by the eolonization eyele.

2. The eauses of the drift must be sought espeeially in the mechanieal effects of the current, but many other faetors are of importanee, e.g.

population density, intrinsie striving towards movement, oxygen saturation, ete.

3. Nearly all benthonie animal groups present in the water investigated are represented in the drift.

4. Extraordinarily large quantities of material, especially plankton, make up the organie drif't below eutropbic lakes, but the amount of material is usually surprisingly high also dowDstream of oligotrophie lakes.

5. Lake organisms in the drift, to a small extent, are in general to be found far do~mstre8~ of the lwre.

6. There are remarkable peaks in the amounts of drifting organisms at dawn and sunset. For some freshwater invertebrates this is due partly to an endogenous rhythm of loeomotor activity and partly to the action of the light. The organic drift was collected in nets, one with plankton gauze, the other with a special "paddle-wheel apparatus".

The former was put in the watereourse usually for one or two hours at a spot with a known eurrent veloeity, to allow us to estimate

satisfactorj.ly the total aJ.i10unt of water whieh passed through the net, with corrections for sil ting up of the net etc. The l1paddle-wheel apparatus" has ^Et net with et l Imn mesh. It gives the total amount of the drift, ~nth the exception of microscopie organisms and silt.

Abbrevations.

Phy

=

phytoplankton, Zoo

=

zooplankton, Det

=

detritus, Ino

=

^inorganic

compounds of the drift, Tp

=

traces of plants, Ta

=

traces of animals, Wa

=

aquatic animals, such as black-fly imagines, spiders, etc. The figures represent an estimation of the amount of the respective kind of drifting organism: O

=

^{none, l}

=

^{same few, 2}

=

a considerable number and 3

=

masses in the drift. The predominant species are given under the figures.

Lee. Plankton gauze Paci:lle-whoo l apparatu3 3 Speci es pt'esent

Pht ^{Zoo Det lno Tp Ta l/a Aa} Ino Total,ml/m (Dot. ^f3, !'Breins.. lum)

A 2 2~3 2 2 l 4 Brachionus fa lcatus, Tric"ocerea cfr. graci ]is,

Ptygura sp.} Rotatoria sp., Synedra navicula,

&Jelloidea

B 2 2 O O 2 Cer:l1alaJella sp., SilP,ulium sp.

C 2 2 Ptygura sp." lliel10jdBa

D 2 1~2 2 2 O O 13 &JelloidGa, Lecane inopinab sympaJa, Synedra sp,

E l l 2 O l Testurhella patina, Cladothrix dichotoma, C1GStBriu~1

Sff', Area 11a sp., Cyclops, AJona sp., ChirorKxnioe0, Ephemeridue

F 2 2 l-Z 2-3 2 Z 35 Tes+l:diml1a patina, Clostcwium sp" Areella :"[}.,

Synedra sp., P'lecoptot'3, Nematoda

G O 3 1 2-3 2 Tostudir.eiia patir.a

H 3 Z Z l-Z 1-2 5 Locane bUll a, L- luna luna} L haliclysta, L

Notrmma sp" N. copaus, AlbBrtia cfr. naidis, della cfr. graci lis, H3brotrocha sp., Rotatoria sr.,

S~irogyraep.., Cosmarium sp." Closterium sp., ~l:J\/icu;:

n~ salOO conditions as at locality Hare to be sI", sp.., Centroro/:i is di scoidea, Mona sp"

€l<pectro. Difflugia sp., Culicidae, Oligochaeta, Ephem., Chi!'"

Simulium sp,., kcella sp.• , Corixa sp.

J 2 2 Z Z l-Z 15 Euchlanis triquetra, Closterium sp., Pimularia sp,;

SyuDra SP';' Areella sp" 01i gcch.^J Eph., ~t.

K O 2 Z l J-Z 3 10 Osci l; :tori asp., Synedra sp.

l 2 2 Z-3 2 2 2 2 18 Closterium sp,^l Osci1liJtoria sp.., Fragi l1aria sp.,

Nav;cula sp.^I lJitzschia sp., ftnkistraJesmus sp.., Areella sp.. , Syn:;dra sp.• , &Jel1oidea, l.Jc«atoda, Simlllium sp.

H 1--2 O 2 l-Z '" Plecoptera, SimLl1illffi sp,

N Z 1--2 2 1-2 Z O 3 35 Bde lbde3, Tf'ic:hoptera Simlllium Sj)"

ClostGrium sp.; Chir,

O Z-3 2 2 Z 2 2 Z 20 sp.^I Chlr, ,

Closterium sp,

R 2 O 5 Pinnularia sp, SL,~'ire11asp" Navicu]a sp.,

Closteri lim sp.. , Ud811oidoo, Namatroa

The organic drift was poor or very poor, compared with European or N American conditions This is true even considering the facts that the investigations were carried out during the day·.time, no samples were taken at davm or sunset, when the drift may be expected to be richest, and that most localities visited were located far 8~ay from lakes or pools which serve as c drift ers.

TABLE V. Macroscopic animals in the stream per 1,000 cm of representative bottom substrata.

The number (No.) and weight (Wt) of each animal group are given. In parentheses under "Simuliidae present" are noted the most common stages of the larvae (l) and sexes of the pupae (p) • Figures underlined ^give actual number surely parasitized immature stages; Tvi == Mermitidae, Mi == Microsporidae.

[ph Tri Pla Chir Slfill1 Oth Tota 7 Simu7iidae present

No. 1ft No. 1ft No. Itt No. Ht No. Ut No. Ht No. \,tt

A 2 5 12 260 12 7 2 5 3 125 37 ^4(E 32 1(4~6, 4Hi) +2 P(0"+o) S. damnoslJffii

- +

~4 7 (4-6,] N) S. kol1/89.

B 7 15 40 9 56 20 1(4-6, 6 Mi) +10 p (50"+50, 5 ['ii)

- + -

S. damnosumi 6 1(3-6, 1f·1\)+11 p(4 ci"+

70, 8Hi)S. 1-':'lnfae;

"3

^1{3-4)+75 p

+ - - - - -

(2 eft 13 0, 7~1i) S. unicornutum; 5 p (2 r?+3 o)s-: a]cocki.

+

C 20 20 No larvae. t1any fema les of S, dalJ1!1(}')',ffi aroU:,j

O 12 23 5 40 4 32 12 5 13 22 4 47 126 3 1(5-6)+2 P(e?'+ 0, l 111) S.

8 p (3 0"+50, lili

t f

schoutfidsni, + -

E Nothing. f1lavy procipi tation.

F ^If 12 2 11 14 10 ^{3 2 2 7 25 42} 19 ](3-6, rnainly 4, 2 Ni) +78 p (8

100,_{t -}3 Hi) S. akocki ari.J S. a1ccd<i_{- , - - - _ _}

o

occldenta Ja,: 'j] "1(11-6, mai dy G, 3 (2 d"+2O, l Ni) S. uniGorntiu:n.-

+ -

6 2 6 7 2 1 3 2 3 20 77 36 2 1(3-4) S, (Eusimuljum) sp.; 1 1 (2) S,

H 5 19 19 ffi 6 2 2(15 80 2 80 2J7 268 f'lany 1arvae in 1-2 St2lpS, not det8rmin:,~1

hEre. 34 1{3-6 of which 10,5-6, 4Ni) +fl ii

(4r?'+7 o, 211i)S. m'EdusaefonMa; J7(3) S. (Eus,)\p.,; l plC')S aicocki ie.'i,

5 15 2 9 3 2 38 35 2 24 49 85 34 ](usual]y 3 stage, 8in5~6, 2 Ni)t

70 P (6 flit 4 o, 2Ni)S. mOOuS3eforweoi 2 1(3&5) +

t

^p~o) S. a1cocki; 2'1(5& 6)

.l.

S. ruficorm. '

J 3 3 2 6 6 3 11 14 g ](4-6, 1 Ni)

s.

damn03uffi; 16l(4~5, Hli)

S. a1cocki; 3 7(2) .S. ^{SJ), -}

K 8 27 2 11 7 35 2 5 19 78 2 1(4&6)S,c<''>-'';l'J1cuori (7), Abovo afar!

2kmdOWffitream 900 l!J;roJ cm2. On 76 1(50 in 4-5, 26 in 2.,3,

E

!'ii)~,

ryasa 1andicuffi,

KJ 3 7 3 11 16 70 3 2 25 90 2 1(2&4) S.. hirsutum (7); 11(" 4) S.

l 8 41 9 82 3 28 3 _l~ 470 4 450 22Ji1;T"2 180 ](74in 5--6, 7!'Ii, 84 in

!:.

^iii, ?2 in 1-2) +14.p (förili) s,

M 30 55 16 48 70 25 70 120

-

^{186 248 18 7(12 in 5~6stagas) +]II P (4 Hi)}

S. if /(4.5) S. darr"::';!)f!).

N 23 40 10 'öl 2 21 78 47 140 510 6 36 259 741 9!t 7(3-6, mainly 5,~Ni) ^$" ka:n':z'iL:m.

R

no

^{190 27 92 7 31 54 22 - 202 ]1·,0 41(4.6,.lni) S. ni1i (?).}

76 170 6 1(3-6, 1Hi) +6p(3 i'H) S. flBdusa§forlOO

form harwoavEBi; ll(if} S. akeiCki {?};

9)(2-4) :I-4p ~ Hi) S. (Eusioo1ium) sp.

- ]l,l 289 101(4-6, 7 i1i) +5p (3c1'+2 o) S. kauntzeum;

4 1(M) +2p (O,S. dentu1osu~ ^{s. ).}

? ? ? ? 61(4·5,2Hi}S. demu1osUffi.; 3l{3-4) S.

auroosimile (?); 2giam (121ffi1) l, prD"/:abjy

no,1 spocj$,

Lx. Eph No. Hl:

01135

P 4 13

Q ? ?

Tri No. Hl:

2 21

? 7 Ple No. Hl:

3 22

15 92

? 7 Chir No. lit 34 20

ZI 20

? 7 Sil1Ul

~Jo. l'll:

26 72

95 '154

50 7

4 5

Oth No. vit

Tota 1 Simu Ji idao prosont No. lit

BENTHONIC FAUNA

As is ShOWll in Table V, the nwnbers and weights of the macroscopic animals varied considerab1y in the different watercourses investigated.

By checking some 10ca1ities a few hours or days af ter the occasion described, it was a1so found that the benthonic fauna re-organized within short intervals. The values found for African watercourses must be considered to be pOOl' or very POOl', compared with conditions in

Europe and North America, where similar investigations have been carried out. This proved that the bottorn fauna, and especia11y the lIpassive absorbers of food^Il, such as b1ack··fly larvae⁵ are richest imruediate1y downstream of lakes and sha110ws To a1esser extent this is also the case downstream of tributary in1ets. This is m~inly due to the large amount of food in the organic drift downstre8~ of lakes. Other lake inf1uences are in general positive, as regards the bottom fauna. This is illustrated in Table VI, which has been compiled from data obtained from representative 10calities in Skåne and Smål~nd in southern Sweden (15 localities) and Norrbotten _a~d Lapland in northern Sweden (exc1uding the mountain region, 27 localities)Q These data have been compared with African conditions. It is impossible to give definitions of lInormal parts of the watercourses^ll and ilrepresentative localities^lt; here they have been selected on the basis of expericnce. In rrable V, all the African localities (excluding A and F) are lInormal parts of the water- courses". A general survey like Table VI be10w must be very summaryano.

generalized and cannot generally speaking be considered to give true and rea1ly significative valuese However, it gives same indications of value on the distribution of black flieso

The proportionally relatively hi value for black-fly larvae in normal parts of the watercourses in southern Sweden (and this also seems true of African conditions) is due to the relatively larger amounts of

clusters of black·-fly eggs along the streams in southern Svveden, compared with northern Sweden Here the eggs are more concent.rated at lake outlets (mainly in lIfarest streamEJi; in ^ltopen!1 locali ties along the stream egg masses are relatively common also in northern Sweden). The main reason for the cl.i.stri bution of ,:_usters of eggs is probably to be found in the fact that lakes and shallows are collecting mirrors for black flies, especially females, which are migrating in a rambling manner, s for hasts or localities for e • Bogs and swamps are in many respects equal to lakes as collecting mirrors, which

explains the large amounts of eggs in the upper oourses of helocrenous streams. In southern Sweden, with its more open land, part of this llcollecting-mirror effect" of the lakes is lost; the distribution of females to open areas becomes more even and oonsequently this is also the case with egg masses along the watercourse.

TABLE VI. Comparisons between the bottom fauna in African and Scandinavian watercourses, with some data on the distribution at lake outlets and lInormal parts of the watercourses^{li •}

Locality Avoraf]d nurber ard weight of macroscopic anil!li3ls No speci as of per 1,00)

eJ

of ~itiv~ bottoo substrata Simuli idae

Total Black-fly larvao and pupao No. lit No. \It No.% \'Jt%

A-J (tO), 42 ¹⁽⁰ 28 J7 01 16 9

\'Iest Africa

K·R

^(8), 141 ^IfrJi. 01 169 47 43 13

East Africa

A- R(18: 86 238 45 85 52 36 19

SoutI'YJrt1 Swcrlon

lako outlots (7) ~3 801 89 13

PNmml parti (8) 178 Hll 61 13

Ncrthom Swcdon

b~ outlots (lO) 1,rJi.7 ^g'f6 90 22

nNorma1!Xlrtll (17) ₈₅ 35 41 23

The main reason for the poor benthonic fauna in African watercourses may be sought in the fact that there are usually few lakes along the rivers, which means low organio drift. Other factors of importance are the great and rapid changes in the disoharge of water, both

seasonally and oocasionally, and consequently great variations in the current velocity, the fact that many substrata are unfavourable for most rheobionts and rheophilous organisms, because of precipitation of silt and humus; in tropical rain forests streams are often darkly shaded and light is usually a positive localization factor for the benthonic fauna; chemically the waters are rather poor (the

surrounding Quaternary deposita are usually laterites, with few

nutrient salts); very hard oonditions (intense sunshine, heavy rains, terrific competition, etc.) for imagines af ter emergence from the water stages, which affect the colonization cycle unfavourably.

TABLE VII. Observations on black flies.

The different species found are presented below with notes on

ecological factors of a certain interest. The figures in parentheses give the actual numbers of larvae and pupae per 1,000 crn 2 of

representative bottorn substrata.

Specios LocQ lity

S. d3fnnooum (s. 1.) A(Z),B(3), 0(5))(Z), L( Hit) i1(ZO)

Abundant in currcnt substratum vo:ocitios stonDplant

0);·1.4 (+) +

Proportions stono/plam:

1/15

%PnrasHiziXI 4-6 stag$

1&p 11-35

Romarks

AJtitudoof L1,250ffi

Foma1re around 10gs lncrrosod bi ting at sunsot

S. kCfo/oo A(<J),8(Z) S. llnicomutum B(Z),F(J) S. akocki (s. 1.) Bk1l,F(Z),

H(1l,1 (Z), J(1;),0«1l S. schDlftaJoni O(S) S. modusaoformao 1(35),

H(c. 200) S. modusaoformo f. 0(12) hargroavcsi

S. rufico,l1o I(Z)

S. ni 1i R(!t)

K(2) S. ryaS21andicum

Kk

1)1 S, dentulosum (s. 1. )P(30),U(ZS) S. hirsutLm 1(1 (2 ) S. auroosimilo 0(14) S. corviccmutum 1'1(63) S. kauntzOl1ffi N(VtO),P(65)

~. (s.str.).1Q: l G(1)rJ«1)

~. (s.str.)~ II 1\1(1) (s.str.)~ III u(10) S. (Eusirr:ulium) G(Z),H(3)

.§!.:I

S. (Eus; mu1\ um) 0(13)

~.II

0.4-0.8

o.

2...0'/;

0.2-0..7, ut O1.2 (s!.<I:Jsp.7) O, S-l. 2 0.3-0.9

o.Z...O.5 0.7 O.8-1.S

o.

Sl 0,3-1.3

0..3 0..3 0.9 0.9-1.3 0.5-0.7 0..3 0.3 0.6-0.9

(+)

+ +

+

7 (t) (t) +

+ 7 7 +

+ + + +

+ +

+

+

+ 7

t

+

7 7

Z5-53 27-38 Q.25

12 13-16

33

o

25 O G. 30

Q.33 O O 13

G, 4 O O O O

14

LO'II Or:at F Low

et

^atF

Tomporary stream

TOO1POf'8ry stream High pH:7. 8

2kmdO'llnstrOOffi: K(900) 1) Onarabs: 76 1 from 40 m2

Altitudo> 2,000ffi

Alti tOOo>- 2,000 m

Altittrlo> 2,000 m

S. damnosum, the vector of onchocerciasis, is the most widespread of the species i.nvestigated. From morphological studies on its characters illld features it is fairly obvious that the species is a complex one@

This will be proved by the cytological investigations which are being carried out in Canada and Sweden~ If there are siblings, same of which Cilll transmit the filarial worm Onchocerca volvnlus and same of which cannot, it may be possible to introduce lIharmlesslt siblings in areas with vector siblings. By competition the former may exterminate the latter, because they are superior in same ecologica1 respects (O.

volvnlus develops partly in the thoracic muscles of female S. damnosum, which limits their flight range). There are indications that S. damnosum

produc~eggs anautogenously, This may be ,vrong; the indications may be due to environmental factors, such as pOOl' organic drift etc. However, we need more investigations before we can say whether S. damnosum is anautogenous or facultative autogenous (which means it can produce mature eggs without a blood meal, if the food supply is rich during the larval stages).

The number of parasitized black-fly larvae and pupae vary considerably from locality to locality, from species to species and from one larval stage to another. Larvae infected by Microsporidians may pupate and even emerge. It seems obvious that many Microsporidians are species- bound. This makes it possible to U8e some species of Microsporidians (and possibly Mermithids) for "se l ec tive" biologioal oontrol of un- wanted black-fly species. The first stage in our fight against vectors

of onchocerciasis should be the weakening of harmful species (or better siblings) with the aid of species-bonnd parasites. The second step involves the introduction of harmless siblings in areas with weakened harmful populations. To carry this out, we need thorough investigations, limited to certain districts where we may study in detail primarily the ecology, parasitology illld karyology of vector species.

Main EcoloBY

(a) To collect and record data on the prevalence and distribution of the early stages of vector species in all kinds of watercourses within the area.

(b) To establish the minimum length of the larval life of the vector species.

(c) To find "optimum conditions^iJ for larvae and pupae of vector species.

(d) To make observ",ttions on the prevalence of adul t vector species and their appearance in connection with the rainy period. This includes investigations on dry-season survival.

(e) To elucidate the flight range of any particular vector.

(f) To map lillres and pools along the rivers and explore their influence on vector species9 including the llcollecting mirror lt effects of lakes on females and the lakes' role as food-supply reservoirs to the larvae downstream^Q To get the llecological background l1 , data should be obtained on rainfall, variations in discharge of water, prevailing winds,

topography, auxotrophy, etc

Parasitology

(a) Parasites (excluding O. volvulus) on different stages of vector species (l) in and around different parts of various watercourses and (2) in relation to population density.

(b)

O.

volvulus (l) Total number of vector specimens dissected,

(2)

proportions of infected to non-infected in ferilllles of different ages;

(3) number of infective-stage larvae.

Karyology

Mapping of salivary-gland chromosomes of larvae of vector species from all localities investigated, to find siblings and to relate them to the distribution of onchocerciasis.

SUMHLARY

Investigations carried out during July and August 1965 and 1966 in African watercourses in different vegetation zones revealed poor or very poor benthonic fauna. The main reason for this may have been the low organic drift in the watercourses investigated, but other factors have an influence, such as rapid changes in the discharge of water, usually heavy precipitatians of humus and sil t on the substrata, low concentrations of nutrient salts in the water and a very hard " s truggle for life" for imaginal stages around the stream, which may afflict the colonization cycle unfavourably. For the black-fly larvae, among others, S. damnosum, the most importm1t enVirOnlllental factors influencing the distribution seem to be (a) food supply, (b) substratum, (c) current velocity, (d) light, (e) depth, (f) physical and chemical conditions, and (g) pollution. Many factors are more or less interdependent;

however, they are more easily surveyed when considered as independent factors. These are not listed according to their importance; this would have involved gross generalization. The number of parasitized black-fly larvae vary considerably but must be classified as rather high. There are indications that many Microsporidians are species-bound.

The methodology used was suitable for getting a broad and comprehensive picture of the benthonic fauna.

REFEHENCES

Basrur, V.R., Inversion polymorphism in the mloge Glyptotendipes barbipes. Department of Botany, University of Toronto.

WUrzburg 1957

Carlsson, G. , Opusc. Ent, , Suppl. 2L Lund 1962 Carlsson, G. , Bull, W.H,O, 37, 1967

MUller, K

, z.

^{Ölwl, Tiere} 56, 1966 Rothfels, K., J. Hered. 47, l 6

No. l. Meyer-Heiselberg, R., Nates from Liberated African Department in the Archives at Fourah Ba~

Colle~e, Freetown, Sierra Leone.

Scandinavian Institute of African Studies, Uppsala 1967, 61 pp.

No. 2. Widstrand, C.G" Lyrics of Social Protest in East Africa.

Scandinavian Institute of African Studies, Uppsala 1968, (In pre- paration).

No. 3. Carlsson, Gunnar, Benthonic Fauna in African Watercourses z with Special Reference to Black-Fly Populations. Scandinavian Institute of African Studies, Uppsala 1968. 13 pp.