-

.. ~

" ...... J \, "'...!~ _t'

.... ~ ......

lnsect predators of JarvaJ Simuilum damnosum Theobald, vector of

onchocerciasis, and other Simulium ~cies in Southem .

.'

by -'

Judith A. Schorscher

Department of Entomology

McGill University, Montref4,

@ February 1985

A thesis submitted to the Faculty of Graduate Studies and Research

in partial fulfll1ment of the requirements for the degree of <9 Master of Science.

f -1 -

M.Sc. Judith A. Schorscher Dept. of Entomology , predators of larval Simulium damnosum 5.1. Theobald, vector

of oncho<:erciasis, and other Simulium spedes in Southem Sudan.

ABSTRACT

Over 800 aquatic jnsects associated ..vith the, larval stages of Simulium damnosum s.l. eollected' from Wau (Bahr-el-Ghazal Province), Southern Sudan, were

disseèted and thek gut contents analysed to determine the importance of larval

<:> 1 , black flies in their diet. , Rates of predation, numbers of different prey items in the diet, prey,

preferences, variation of diet with age and seasonal distribution of the predaton

were recorded.

ln Southern Sudan the inseet exerting the greatest pressure on Jarval - Simuliidae is Cheumatopsyche digitata (Hydropsychidae: Trichoptera). It's j~portance

may be attributed to it's high carnivory, it's preference for black fly larvae ôver

other prey ite"ms and it's abundance. It is followed by 1 Ch. copiosa, a less

carnivorous $pecies whose impact is due 'l'ainly to it's ~igh densities. Other

with the potential to reduce blaek tly populations are Zygonyx Spa

(t.ibellulidae: ), Neoperla sp. (Perlidae: ~Iecoptera), and Cheumatopsyche Spa

VlIJ. These three species, consumed the highest mean numt?er of black fly larvae pcr

individual, and did not prey extensively on other important predators. Ali age

:.---~ classes of Zygonyx were highly carnivorous and fed preferentially on Simulium

Jarvae. However, Zygonyx, as weil as Neoperla and Cheumatopsyche Spa VIII , occurred in relatively low densities.

,----._-_ ...... , _.._.- -_.-- -11-

Les insectes pré dateur~ des larves de Simullum damnosum ,:tneobald,

le vectetl( de l'onchocercose, et d'autres espèces de SjmuÎium,

dans le Sud ~ Soudan.

- . ,

RESUME

Plus de 800 insectes aquatiques associé s aux stades pré imaglnaux de Slmultum

damnosum 5.1. et collectlonés dans la région de Wau, province du Bahr~el-Ghazal (Sud Soudan), furent disèqués et leurs contenus stomacaux examtné!; pour détermtner l'importance des larves de Simulies dans leuf' régime alimentaire

Les taux de prédation, le nombre de différentes protes dans l'estomac, les proies préferées, la variation du régime alimentaire avec l'age er la dlstnbutlon • '> saisonière des pré dateurs furent étudié s. L'espèce exerçant-la plus grande'- pression sur les populations pré imaglnales de

Simulies est Cheumatopsyche digitata (Hydropsychldae: Trlchoptera). 50n_ importance . - stexplique par sa grande ,voracité, sa p~éterence pour les larves de Simulies et ses

grands> nombres: Cette espèce est suivie par Cheumatopsyche copiosa, un I~secte

moins vorace que son prOChe parent et dont l'impac~ peut surtout être attribué a sa haute densité.

D'autes espèces q~,i ont te potentiel de réduire les populations de SlmulJes

sont: Zygonyx $p. (libeUuJidae: Odonata), Neoperla sp. (Perlidae: Plecoptera) et

CheumatopsYche sp. VItI. Ces trois espèces consomment les taux les plus é I,evé s de Simulies et ne se nourissent que rarement d'autres pré dateurs Importants. Les

Zygonyx de toutes tailles sont exclusivement carnivo,res et se nourissent preterentieUement de larves de Simulium. Toutefois les dens! té s de Zygonyx amsl que de Neoperla et CheumatopsYche sp. VlII, sont relativement peu élevées.

------_ .._ .....-. -----_._- _.. _--- -.------~J -111-

"

Short title: PREDATORS OF LARVAL 8LACK PLIES IN SUDAN.

by

Judith A. SCHORSCHER

" - .. "",< " i!''l,1 i ~ ~', f' 1 _"

":lV-

AKNOWLEDGEMENTS

The field work for this project was performed in Wau (Bahr-el-Chazal Region),

Southern Sudan, in cooperation with the WHO (World Health Organization) project

~n "Research into the Effectivenes5 of LocaHzed Onchocerciasis Vector Control in

Bahr-el-Ghazal Region, Sudan". The author was supported trom 1981 to 1983 by a

Postgraduate Scholarship awarded by the Natural Science and Engineering Research

Council of Canada. Throughout this project 1 received support and help from a large number of people. 1 would like to express my gratitude to the followmg persons:

Dr. DavId J. LEWIS of McGill University, my thesis supervisor, for hlS support, cooperation and guidance.

Dr. Frusal T. ABUSHAMMA, Deputy-Vice Chancellor, UnIVersity of Khartoum, my co-supervisor overseas, for his moral support and help with logistics and the organization of my research.

Dr. Osman ABDELNUR, Senior Government Entomologist, National Public

Health Laboratories, Khartoum and principal investigator of the onchocerciasis control project in Wau, who we1comed me to the project and provided me wlth information and Iiterature.

Dr. Richard BAKER, WHO Consultant Entomologist, who shared with me ail the- facilities at his disposaI, his collections 'of associated fauna and his wealth of knowledge of Simullum ecology. 1 am grateful for his constant encouragement, fruitful discussion, enthusiasm and friendship.

! 1 , .------v-

" Dr. Kt.\MBAL from the Department of Zooiogy, University of Khartoum for

hls kindness and praétlcal assistance wlth -nany mmor problems.

The graduate students of the Departme"nt of Zoology, UnIversity of Khartoum,

who welcomed me warmly and assisted me wherever they could. "'y special thanks

go ta Ahmed e.l BAKRI, ABU GASM and HOUDA.

"'Ir. Paul OCfLO, Mr. BatIsta 'JORO, \Ar. ElunaJ Ka}okole YOBü50N, \1r. John

Joseph UCIN and \Ar. Nixon Ali MATTHEW k,mdly asslsted n'le tn the collection of

specimens tram the river. Mr. OelLO and Mr. NORO also helped wlth the sortlng

of specimens in the laboratory. would Iike ta express my appreclatlOn of thelrO

thoroughness and competence. ~r. Splritu LEONE and Saeed Awad 15\1AIL

participated as chauffeurs to most samplJng expeditlons.

Mr. Ali Gasm el SID, felJow student m Wau for his kmdness tn provldmg me

with extra specimens of Plecoptera nymphs from hls personal collection.

1 Dr. Terrie TAYLOR 0.0. physiclan wlth the Michigan State UnIversity

Onchocercisis project in Wau, for her stimulating friendship and spint of sClentiflc

" cooperation as weIl as her cheerful hospltality both in Khartoum and Wqu.

Michigan State University for the loan of a binocular mIcroscope and

laboratory space. J', Herr Rolf HAASE of the "Abili Girls Senior Secondary School, (\1bili,

Bahr-el-Ghazal Province) for his generous hospitality and friendship, which greatly

enhanced sampHng expeditions on the Sue River.

The members of the JUR communities of Mbdi and 1\Iyiduk for their welcome

and assistance in collecting specimens. -v~-

Dr. T .R.E. SOUTHWOOD, Oxford University, England, for his welcome and

assistance.

The following members of the British Museum of Natural History, London for

their prompt identification of specimens: Dr. P.C. BARNARD (Trichoptera), Dr. P.S.

CRANSTON (Chironomidae), Dr. S.J. BROOKS (Odonata and Ephemeroptera).

Dr. 'L. LANDS BURY of the Hope Department of Entomology, Oxford

University, for identification of the Hemiptera.

Dr. P.J. BOON, University of the West Indies, Kingston, for his interesttng

corespondanre and for. forwarding me a copy of a manuscript in print as well as. ,J EM photographs of Trichoptera proventricular teeth.

Dr. H.P. ZWICK, Limnologische Flussstation des Max-Plank-Instltüts fur

Limnolo~}e, in Schlitz, West Germany, for identification of Plecoptera nym~hs. -,

For numerous repr~nts on the taxonomy. of tropical HydrQpsychidae, Dr. B.

/' STA TZNER, Zoologische Institut, Karlsruhe University, West Germany and nr. K.

SCOTT, Albany Museum, Grahamstown, .

Dr. René LeBERRE, Director WHO' Vector Control Unit, Geneva, for

stimulating discussion, encouragement and support.

Dr. J.-M. ELOUARD and Mr. F. GIB~N, Université de Paris-Sud, for sjlaring

their extensive knowledge of ,aquatic invertebrates associated with the larvae of

Simù1ium damnosum and providing me with unpublished manuscripts.

------vii -

~ r. P. LANGLOIS, Senior technician, Department of Entomology, \AcGill ,1 University, far;~'hls advice and assistance wlth ail aspects of photography. '1 '11 ..

In Khartoum, Didier and Corinne RE'v\Y, for their frendship and help through dlfficult moments. Pascal GINAILHAC for his invaluable assistance with logistics, and Father Hubert BARBIER for his ald in shippmg equipment down ta Wau.

David LEYIN- for his friendship, constant moral support and patient preof rèading of the text.

DaVid GORDON and Gérald LAFLEUR, fellow students in the Department of

Entomology, for. their assistance with statistics and the use of the computer.

'\Ars. J. TAYLOR, Department of Entomology, Macdonald College, for patience and helpfulness. in printing the text.

\ 1 Wayne FAIRCHILD and Richard WEBBER, feHow laboratory companions in the

Department of Entomology, for théir ~e

" - - -_.. _--~_ .._,---_.-.~------~ f' -vi i i-

TABLE OP CONTENTS

ABS'TRA.CT ••••••••' •••••••••• _ "le ...... , ...... i

B!S1JItE •••••••• ., •••••~ •••••••••••••••••••••••••• ~ ••••••••••••••••••••• i'i

~ •••••••••••• _ ••••••••••.• _ ...... iv

. , ". LIST OF lICO'BBS ...... _ ...... - ...... xi 1

LIST OP T.ABt.Es ••••••••••••••••••••••••••••••••••••••••••••••••••••••xiii

'IBTRO.DIJCTI,OR.. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •••• ., • • .. • • • • • .. .. • • • • • • • • • •• 1

LI'rE1lATD'RE 'REVIEW ...... 2 \ "BLACK nIES AND ONCHOCERCIASIS •••••••••••••••••••••••••••••••••••• 2

Life cycle of Onchocerca volvulus ••••••••••••••.••••••••••••••• 2

Distribution of Onchocercias is ••••••••••••••••••••••••••••••••• 3

Pathology •••••••••.••• • •• li .4

Therapy •••••••••••••••••••••••••••••••••••••••••••••••••••••••• 4

Impact of Onchocercias is ...... 5

Control of Onchocerciasis ••••• • •••••••••••••••••••••••••• 5

r PREDATORS OF BLACK FLIES •••••••••••••••••••••••••••••••••••••••••• 9

Trichoptera •••••••••••••••••••••••••••••••••••••••••••••••••••• 9

Plecoptera ••••••••••• :•• a. •••••••••••••••••• ., •••••••••••••••••••• 11 l '

L Ephemeroptera •••••••••••••••••••••••••••••••••••••••••••••••••• 11 " Odonata: ••••••••••••• r: ...... Il ...... 12'

Diptera ...... '•• 1•••••••••••••• ~ •••••••••••••••••••••••••••••• 12

o ther Groups ••••••••••••••••••••••••••••••••••••••••••••••••••• 13

Predators of Black FI ies in Areas of Endemie Onchocercias is •••• 14

lNTERPRETING QIET FROM GUT ANALYSIS ••••••••••••••••••••••••••••••• 16

visual analys ia of gut content's •••••••••.•••••\ ••• 'l ~ •••••••••••• 16 \ SeroJogicaJ me thod ••• ',' •••• '" ••••••••••••••••••• ~,' ••••••• ~ ••••••• 17

.. ~'l

-ix-

HATB~ ABD HETHODs •••••.••••••••••••••••••••••••••••••••••••••••• 18

STUDY AREA • ...... • •••••••••••••••••••••• • 18 " . INSECT COLLECTIONS •••••••• ft ...... 'il, • •••••••••••••••• 19

Sorting ...... , ...... · ...... <. ....•••.. • 20

Identification •••••••••••••••••••••••••••••••••••••••••• ~ •••••• 21

GUT DISSECTIONS •••••••••••••••••••••••••••••.•••••••• • I"J• ••••••••••• 21

NUl-fERICAL TREAntENT •••••••••••••••••• If ...... ~ •••••••••••••• • 23

'RESUL'rS ...... ,."" ...... ;~. "' ...... 27

GENERAL COLLECTION •••••••••••••••••••••••••••••••••••••••••••••••• 27

GUT DISSECTIONS ••••• ...... • .••.••.••••••••• ~21 \ Main Predators as Determi.ned by Gut Dissections ••••••••••••••••'i8 1 Determination of Prey. · •.•....••••..••• • 30

DIET COMPOSITION •••••••••••••••••••••••••••••••••••••.••• • ~,. .••••• • 31 " Percentage of Differ'ent Prey Items in Gut ...... 31

"Mean Numbers of Prey Consumed per Predator ••••••••• ~ ••.••••••••• 32

Compa~ative Importance of Different Predators ••• ~ •••••••••••••• 33

Variation of diet with Age ••..•••••.•.•••••..••••...••••.•••••• 34 c SEAsO~Ai DISTRIBUTION OF PREDATORS •••••••••••••••••••••••••••••••• 34 "

DISCUSSION •• Ct ...... 1 •••••• _ ••••••••••••••••••••• _ •••••• ~ ••••••• •• 36

GENERAL COt-fliENTS •••••••••••••••••••••••••••••••••••••••••••••••••• 36

tRICHOPTERA •••••• 0 ••••••••••••• o' ~ •••••••••••••••••••••••••••••••• • 37

Hydropsychidae ••••••••••••••••••••••••••••••••.••••••••••••••.•••• t7

Cheumatopsyche ..• : .....••...... ••.•...•••.....••..•.•••.....••. l8 , J

i Cheumatopsyche • •••••••••••••••••••••• • 39

~mpetiL:~on~ •••••••c • ...... •...•••••.....•• . 39

C~nnibaltsm •••••••••••••• . ••...•.•••••.••••....•• •. 41

" -x-

Cheumatopsyche copiosa ...••.•.•••....•••••....•.•••.•.••...••.• 41 'Cheumatopsyche falcifera......

Cheumatopsyche sp. VIII ...... •...... ••...•••.•....•...... 43

Amphipsyche sene~alensis •• ~ •••••••••••••••••••••••••••••••••••• 45

Aethaloptera dispar •••••••••••••••••••••••••••••••••••••••••••• 46

Trichoptera other than Hydropsychidae ••••••••••••••••••' ••••••••••• 47

Chimarra (Philoptamidae) ...... •....•...••...... •.....f • • ~7

. . ( , HydroptLlLdae ••••••••.•••••••.••••.• /ri ••••• fi •••••• ~ ••••••••••••• 48

Oecetis (Leptoceridae) ••.••••••••••••••••••••••••••••••••••••• • 4~//

An Epilogue to the Trichoptera ••••••••••••••••••••••••••• '••••••••• 49

PLECOPTERA ••••••• " •••••••••••••••••••••••••••••••••••••••••••••••• 50

ODONATA •••••••• • •••••••••••••• III ...... •...... 52

Zygonyx •••••••••••••••• : •• a ••••••••••••••••••••••••••••••••••••• 52

Olpogastra ••••••••••••••••••••••••••••••••••••••••••••••••••••• 53

Paragomphus or Crenigomphus •• ,!.__ ••••••••••••••••••••••••••••••• 54 r t:f!" CHIRONOMIDAE ••••••••• ~ ••••••••••••••••••••••••••••••••••••••••••• • 54 d, OTHER POTENTLAL PREDATORS ••••••••••••••••••• •••.••• ; 5S

Philacollus (Dytiscidae; Coleoptera).~ ••• ••••..• . 55

VARIATION IN DlET WITH AGE •••••••••••••••••••••••••••••••••••••••• 55

SEASONALITY OF PREDATORS •••••••• ~ ••••••••••••••••••••••••••••••••• 57

IMPORTANCE OF PREDATORS ••••••••••••••••••••••••••••••••••••••••••• 58

CONCLUSION •••••••••• ,. ••••••••••••••••••••••••••••••••••••••••••••••• 59

REFERENCES ••••••• • 1& •••••••• ~ ••••••••••••••••••••••••••••••••• ••.••.•• 61

APPENDIX 1: Line drawings of the most important chitinous parts,

used for deterpining prey origin •••••••••••••••••••••••• 83 -xi- .:

" APPENDIX 2: Testing the hypothesis that aIl prey categories occur

with equal frequency •••.•.•••••••••••••...•••.•.••••.••• 88

APPENDIX 3: Analysis of variance on mean numbers of prey consumed

by nine predators collected in the.presence of

simul ium larvae •••••••••••••.•.•• : •••••..••••••••••••••• 89

APPENDIX 4. Tukey's w-procedure: Testing significant differences

between mean voracities of nine species of predators •••• 91

APPENDIX 5. Head measurements used to determine size class •••••.•••• 92

APPENDIX 6. Analysis of variance on the mean number of prey items

consumed by each class size of nine predators collected

in the presence of Simulium larvae ••••.••••••••••.•••••• 93

APPENDIX 7. Patterns of proventricular teeth •••••••••••••••••••••• :.96

1 -xii-

LIST OF FIGURES

Figure 1. Map of Southern Sudan .•••••.••••••••.•••••• : •••••••••••••• 70

Figure 2. Map of samp1ing sites near Wau (Bahr-el-Ghaza1 Province) •• 7l

Figure 3. Percentage of different prey items _peL'" predator ••••••• '•••• 72

Figure 4. Comparison of the percentage of different prey items

found in the gut~ of two Hydropsychidae co11ected in the

presence and absence of Simulium larvae ••••••••••••••••••• 73

Figure 5. Mean number o~, prey items per predat?r •••••••••••••••••••• 74

Figure 6. Comparative importance of oine predators in controlling t larval black fly populations, assuming aIl predators are

present in equal number"s ...... •••.....•...... •....•.•..•. 75

Figure 7. Comparative importance of ni ne predators'in controlling

larval black fIy populations, taking into account their

annuai relative abundances •••• : ••••• : ••••••••••••••••••••• 75

Figure 8. Variation of diet composition depending on the size of

the predator •••••••••••••••••••••••••••••••••••••••••••••• 76 "'-',

Figure 9. Variation of seasonal relative abundance of the predatory

fauna •••••••••.•••••••••••.•.•••....•.•••..•.••••••••••.•• 77

-- f -xiii-

LIST OF TABLES

~able 1. List of aquatic insects from lotie habitats of the Wau

area, Southern Sudan ••••••••••••••••••••••••••••••••••••••• 78

Table 2. Results of gut analysis of 19 species of inseets

c~llected in association with larval black flies, with

percent~ges of specimens positive for Simulium larvaec ••••• 80

Table 3. Voracity values for each species of predator associated

with Iarvai black flies in Southern Sudan •••••••••••••••••• 81

Table 4. Voracity values per size class for each species of

of predator assotiated with larval black flies ••••••••••••• 82

1 (

o

--...... -...... t -1-

INTRODUCTION

Onchocerciasis, commonly known as river blindness, is endemic to C;outhern

Sudan where numerous rivers originating from the Central African/Zaire

- watershed flow northwards over a wide ironstone plateau. Most of these rivers offer numerous vector breeding sites and although the region is not heavily populated, almost every nverine community is severely affllcted with the disease, and high levels of bllndness are common. t \- Chemotherapy of onchocerciasis IS difficult and partlculartly hazardous ln cases with occular involvement. 50 fa~ efforts at reducing the levels of mfectlOn and transmission of the disease are dependent upiJn control· of the vector. Presently, the only means of vector control are éhemical, with blologicaI' Insecticides being used in sorne Clrcumstances. There is relatlvely little mformation concerning the natural enemles of the vector and the predators especially, are poorly kno Although it is Improbable that predators could be used alone as effe ive control agents, they haye the potential to be important elements in a multi-faceted approach to onchocercÏélsis control., , The pur pose of this research' was to a) identify the predators of black flies in the Wau area, Southern 5udan, b) determine the diet composition and preferred prey of the main predators and c) compare the importance of different predators in controlling larval black fly populations and Identify those with the most potential.

t -2-

LITERATURE REVIEW

BLACK FLIES AND ONCHOCERCIASIS

Onchocerciasis, or river blindness as it IS more commonly known, is one of the most formidable ·infectious diseases of tropical reg ions. It is caused by a f ital' ial worm, Onchocerca volvulus (Leuckart, 1893), which is conSldered to be malntained in nature entirely by interhuman transmis!liOn, although there have been records of natural Infections occurring ln primates other than man.

These appear, however, to be accidentaI and the disease is not considered a zoonosis (Nelson, 1965). This Warial nematode is transmitted by nematocerous flies of the genus SlmuJium. In Africa the main vectors belong to the

Simulium damnosum Theobald species complex.

LIFE CYCLE OF ONCHOCERCA VOLVULUS.

, When an unmfected female Simulium bites an infected persor'J, it ingests a O· number of immature non-infective microfiJariae along with the mgested fluids.

These microfilariae are transferred' with the blood meal to ~he mid-gut. From there a number migrate through the peritrophic membrane to the thoracic muscles where the larvae develop for approximately six days and undergo two moults, after which they become infective and migrate ta the salivary glands~

These third stage larvae àre brought into contact with human tissue via the saliva when the fly next bites. They penetrate into the connective tissue of the skin and the superficial Iy~phatic vessels of the host where they undergo at least two more developmental stages before becoming mature (Hunter et al.,

1964). In most cases the presence 'of the adult worms provokes a local p inflammatory reaction followed by fibrous encapsulation and the eventual \ production of a subcutaneous nodule (Sasa, 1976). Adult worms may remain

i -3-

viable in the body for up ta 20 years and each nodule rnay cantatn several

female worms WhlCh release large numbers of microfilanae. The young larvae

disperse inta, the subcutaneous and cutanepus lymphatics over a wide area of

the body. During these migratiOns, the micr~filariae may be ing~sted by a lI, biting simuliid th us completing the life cycle.

DISTRIBU'TION OF ONCHOCERCIASIS.

Orlchocerciasis IS widely distributed throughout the greater part of trGlpical Il - [ [. Africa especially in the rain regions and the savannah belt that stretches

across the country from in the West to and in the

East. ThIS is consldered to be the origmal home of the aisease (Nelson, 1970).

It is, however, prevalent in other localized regions within the Arablan Pentn~~la ( and Central and South Amenca (Nelson, 1970). The distribution of the disease . l, is dependent on the ambient temperature which must remain above 18°C for

the parasite to be able to develop and survive in the black fly, and on the

distribution of the vector:s, which breed in weil aerated fast running waters,

ranging from mountain torrents to large ri vers and even temporary or

semi...permanent steams. The adult flies may be windborne over extremely long

distances; more than 200 km i5 common (Walsh et al., 1981). This allows them

to reinvade temporary habitats and areas from which they have been

eradicated. The disease mainly affects populations WhlCh live close ta the

vector breeding sites and are exposed to very.high densities of infected black

mes.

More than 20 million people throughout the world are affected by

onchocercïasis (Buck, 1976). Countries with endemic onchocerciasis include:

Senegal, Sierra Leone, , , Mali, (ex Upper Volta),

Ivor,Y Coast, , , , Chad, Cameroon, Centra! African RepubJic, •

M· ___• _____~ -4-

Zaire, , Tanzania, , Ethlopia and Sudan ln i\frica, and Yemen and

Saudi Arabia in the Middle East. Affheted countries withm the Americas

include Mexico, Guatemala, Venezuela, Columbia, Brazil and a recentJy

discoyered foeus in Ecuador (Arzube, 1982).

PATHOLOGY.

Onchocerciasis iS'a chronic condition whose mcreastng pathogenicity

depends on continuous and prolonged exposure to bites by infected flies. T~us,

the disease most seriously affects, adolescent to elderly people, depending on

the ra te of transmission (Wadsworth, 1977). BHndness is the most feared

consequence of the disease whose clinical manifestations are initially

derrae.tologicaJ. The transmissiOn rate ln a certain area is determmed by the

densiiy of the mes, the percentage of infected flies and the microfilarial

density in the-_ human population (Gra ~~ma., 1966). E ye l,esions oc~ur in people

who have been subjected to numerous infections over a long p'enod of tlme and

there is a relationship between the microfilarial density in the upper body and

head region and the occurrence of eye lesions (Nelson, 1970).

THERAPY.

The present means available for treating onchocerciasis are lengthy and

frequently induce unpleasant, and at times fatal side effects. Patients

undergoing chemotherapy require continuous medical supervision. The objectives of current research relating to chemotherapy are to determine the safest and

most practical schedules for treatment of patients and to develop new filariddal compounds, the mast pressing being the development of a safe drug tha t w 111 km or permanently sterilize the adult worms (W.H.O., 1983). Since the most serious clinical manifestations are caused by the host's inflammatory

------(1 -5-

response ta dead m icrofilariae, the use, of microfilaricide5 15 extremely

difficult. Research, however, is being undertaken to better our understandmg

of the mechanisms of immune re5ponses to the parasite (Duke, 1976).

IMPACT OF ONCHOCERCIASIS. (, \ Onchocerciasis is mainly a disease of rural areas. It's distribution i5 such

tha t i t affects most severely people who live close ta 'river valle ys in the

African savannah. In highly endemic areas the rate of blindness may reach_ 10% )', of the infected population. Onchocerciasis has been incriminated as the mam

reason for the emigration of populations away from fertile river valleys to

more barren land (Bradley, 1976) causing an unfavorable concentration of people

in areas which cannot support them-and resulting in a reduction of already

precanous standards of living. \.

CONTROL OF ONCHOCERCIASIS

Due to the difficulty of treatmg the disease itself, the main thrust of current control efforts is directed' towards reducing the vector populations to a tolerable level.

The year 1982 marked the 50th anniversary of the f1rst attempts to control onchocerciasis by attacking the vector (Davies, 1983). This tirst active control occurred in Chiapas Province (Mexiéo) and consisted mainly in the mOl<\thly weeding of steams (Mariotte, 1963). Today there are onchocerciasis control programmes in many parts of the world. The principal control method used is the application of insecticides upstream of the breeding sites in rivers supporting large populations of black fly larvae.

The most important onchercerciasis control programme operating today 1s the World Health Organizat1on Onchocerciasis Control Program (OCP). Started' -6-

In 1975, the project area covers 700.000 km2 of seve,ri'~ adjo!nmg countries In

West Africa: Oahomey, Ghana, , \1alt, 'Jiger, , and Burkma ® Faso. The chemical used is temephos (Abate ) aA organophosphorous compound, J WhlCh reputedly has tittle impact on the non target fauna; for a review of

temephos with refence to the OCP see Opong-Mensah '(1981+). The long term

use of temephos has, however, resulted m a change of the structure of the

aquatic communities (Elouard and Jestin, 1982; Elouard, (983). In areas where ® the larvae have become resistant to Abate , stronger' and less selective

larvicides such as Chlorphoxim have been tested. Chlorphoxim has a dramatic

effect on the populations of associated fauna and ln the case of the

Tnchoptera has resulted in the disappearance of certam species (Statzner,

1982). Recently the biological insecticide, Baclllus thuringiensis serotype H-14

(~ ..!. H-ll+) has b~en employed wlth success withm the OCp, ln West Afnca

(Lacey et al., (982), in New Zealand (Chilcott et al., (983) and m \1exlco

(GaugJer et al., 1983); it's use, however, is not yet widespread due to the hlgh

cost of production.

The Onchocerciasis Control Programme in West Africa has been very

successful in as n'luch as it has resulted in a sharp" decline in the occurrence

and severity of the disease, especially in young children, and even the èomplete

cessation of transmission in certain areas. The project is nevertheless facmg

serious difficulties such as:

a) reinvasion by parous vectors many of which carry infective third stage

larvae from adjacent non-treated areas. (Garms et al., 1979; Cheke and

Garms, 1983). These reinvading females are carrie'd by the prevalent winds

and may traveJ up to 400 km into the treated zones (Walsh et al., 1981).

b) development of resistance by the vector to the insecticIde (Kurtack et

al., (982) necessitating the use of more effective chemicals which may have a -7- deleterious impact on the associated fauna and the river ecosystem.

, It has become clear that there is a need for a great deal more research into non-chemical means of control. Jenkins (1964) issued a comprehensive Ust of the predators,. parasites, and pathogens of ail medically important Insects induding 5imuliidae. The list of pathogens was updated by Roberts and Strand

(1977). There 1s no doubt that a very wide variety of natural enerryies have been found whenever searched for in black fly populations (Laird, 1981).

Ouring the 1970's much interest was' generated in mermithid nematodes which were considered to be good potential biological control agents. The d)fficulties in establishing laboratory colonies of black fly mermith1ds and rearing large numbers of Simulium as weB as the complexity of the\ host parasite relationship (especially life-cycle synchrony) rendered this alternative unrealistic.

In recent years the attention of researchers has turned to pathogens such as fungi, protozoa and viroses, reveallng a vast and virtually unexploted array of black fly enemies. For a bibliography on pathogens of ~imumdae and othér medically important insects, see Roberts and Castillo (I 9~O). Frost and Manier 0'970, Ebsary and Bennett (1975) and Undeen and Notan (1977) have studied fungaJ pathogens specifie to black flies. More work, however, 1s needed to lrIderstànd their biolo~y and intera~tions with the host before an estimation of the ir potential as biological control agents can be made. Takaoka (1980) investigated the pathogens of black mes in an endemic area of onchocerdasis in Guatemala. AJthough he detected a fungus, Coelomycidium sp., it's occurrence was rare. Tinsley (1979), reviewed the potential of insect pathogenic , ~d viruses as pesticidaJ agents and Bailey (1977) made field and laboratory observations on a virus of black flies. Microsporidian protozoa have been

------'8- ~-- ' recorded from Simuhidae (Varva and Undeen 1981; Colbo 19&Z;:-s~ . however, their Ufe-cycles and means of mantpulating them have yet to be ------, determined (Laird, 198 D.

A recent trend in bla1:k fly biological control research 'nas been to test

various pathogens and parasites that have already been mass pr?duced and are

known ,to be effective controls for the aquatic larvae ~ of other Dlptera of

medical Importance. An example of this are the the experiments by ?weeney and Roberts (1983) who tested a mosquito fungus against blac~~ It would appear, however, that most parasites and pathogens are very specifie and/or

have such complex host-parasite relationships that it is extremely difficult to

Isolate an existing pathogen or para~ite of another group and develop a vanety .,

that wocùd be effective aginst black flies. Yet it 1$ the observatIon of Bacillus

thuringiensis in Israelian mosquitoes, that lead to the development of a

biologicaJ control agent which has been s~ccessful1y used against black flies:

B. t. serotype H-14. This organism, however, is used mainly as a' biological

insecticide and does not have the qualities !?f self maintenance of a bio1ogical

control agent. This is' possibly the direction that most research with pathogens ~ .. l' , will take, i.e., the formulation of effective biological insecticides., It is certainly - \ . l ' improbable that a pathogen will be developed which, alone, wil~ be capable of

maintaining larval populations- of black flies at an acceptable level, under

naturai conditions, over a long period of time. However, the establishment of·

pathogens and parasites in conjunction with other control methods (predators,

habitat management, use of repellents, so.cio-economic changes, etc.) offers a

wide range of chatlenging possibilities. One aspect of biological control of black flies which has received very

llttle attention or serious interest is the use of predators and parasitoids.

Paras-itoids appear to be uncomrnon although sorne cases h'ave been reported

. , \ i ---.~------...... -9-

(End~rlein,.I921; Lewis, 1953; Peterson, 1960tPredators have",been extensively

reported yet relatively few studies have dete~miftetÎthe extent. of their effect

or systematicaHy identified aH the predators affect}ng a specifie pest speci~s.

A. comprehensive review oÏ report/!; ,and studies of black fly p~~dators "·follows.

PREDATORS OF BLACK FLIES

f) ~ , v ~ntil recently information on the )predators of black fliès resulted mainly

from field observations '.which go as far back as Howard '(1884) and Pomeroy

(I916). Both of them observed larvae of Hydropsychidae (Trichoptera) attacking

and feeding upon Simulium larvae. Davies (1981) gave a thorough review of aIl

1 reports of predation on both the adult and immature stages of Simuliidae. A 1 . 0 G . number Of these were m~de white studying other aspects of the fiy's ecology " or the feeding habits of the preçator. 1 shaH review here the most important

of these observations as weIl as those madecsince 1981.

TRICHOPTERA

The Trichoptera are' the most important group of aquatic invertebrates"

which prey on SimuJiidae (Service and Elouard, 1980). R~cords incJude members

of ni ne different families; these are Hsted by Burton and McRae (1972). The

most important family is undoubt~dly the Hydropsychidae with records. of

predation from numerous geographical locations: Howard (1884), ~omeroy (1916),

and Tsomides (1984, pers. comm.) observed members of the genus HYdropsyche a . . preying on black fiy larvae in the U.S.A., Peterson and Davies (1960) found

both Hydropsyche and Cheumatopsyche feeding on larvae in a Canadian waterfall, and confirmed. their observations -by gut analysis. Twinn (1939)

mentions an unidentified trichopteran feeding on black flies, frorJi. a fast flowing stream in the Ottawa area. Burton and McRae (1972) studied Hydropsyche and

zntes -tir ---1- ~ -10-

Cbeumà topsyche larvae from Ghana in the laboratory. Under these conditions

,! neither fed on attached simullids, however, both would feast on stray larvae

which entered the funnel of théir nets. Gut dissectIons of field collected

specimens revealed that 10% out of 50 Hydropsyche and 12% out of 25

Cheumatopsyche had fed on Simulium larvae. These results contrast with those

of {:iynes and Williams (1962) for Hydropsyche (3%) and Cheumatopsyche (2%)

o from a Central Africari stream. Crosby (1975) recorded very low rates of

predatior) on simu1iid~ by Hydrobiosis parumbipennis McFarlane in ~ew Zealar;ld,

and Coffman (1967) found similarily low rates in Hydropsyche and

) Cheumatopsyche in North-Eastern U.S.A. Jones (1949) observed high rates of

predation for Hydropsyche (16%) and Petrochemla (20.7%) in Great Britain.

Many Hydropsychidae larvae feed on detritus and algae when they are young "--- and become increasmgly carnivorous as they mature (Muttowskl and Smit~l,

1929). Rhyacophilidae are an important preda tory group m temperate streams: / Jones Cl 949) recorded 16% of Rhyacophila having fed on simull1ds. Although

Rhyacophilidae occur in tropical areas, they have never been incrimmated as

black fIy predators in these regions. Species of Chimarra (Philopotamidae) have

occasionally been recorded as predators of black ,flies: Crisp (1956a) and Peterson and DaVles (1960) observed Chi~arra feeding on large numbers of

Simuliidae, Service and Lyle (1975) and Goyareb and Pmger (1978) detected

( Simulium remains in the guts of Chimarra by, mear;ls of the precipitin test.

) ~ However Burton and McRae (1972) found that Chimarra fed rarely on Simulium.

\ \ (\ Disney (1973) observed hydroptilld larvae of the genus Orthotrichia feeding

on Simulium eggs and pupae. Previously hydroptilid larvae were assumed to be

algal feeders.

" Many of these observatIons- and conclusions are based on identifications to

the generic level only. This could be one factor accounting for the great

/' 1 -11-

variety' and discrepancy of observations, since different species wi~hin the same

genus may have distinct feeding preferences and patterns. The rate of

consumption of black fly larvae by any predator is bound to be influenced by

" c it's prey preference, the season, the respective densities of both the prey and

the predator, the ,avallability of alternative foods and the developmental stages

of bath the victim and the agressor.

PLECOPTERA

Plecoptera are amongst the most voracious predators of black fly larvae

(Crisp, 1956 a, bi Sheldon and Os wood, 1977). In - circumstances where they

, are encountered in large numbers they may exert a strong, depressing effect

on black fly numbers. Sheldon and Oswood (1977) hypothesized that P lecoptera

were responsible for the seasonality of black fly larvae at a lake outlet in

Cali fornia. Hynes and Williams (1962) reported 14-% of P lecoptera from a

Central African stream with black fly remains in their gut. In Brazil, Goyareb

and Pinger (973) found that 58% of Plecoptera gut smears reacted positively

ta black fly antiserum. Crisp (1956a) found NeoperJa spio (Perlidae) to be the

, mast formidable enemy of Simulium in the Red Volta, Ghana. Simmons (1983

\ pers. comm.) found PJecoptera ta have fed extensively on black fly larv;;te in

streams of the north-eastern U.S.A. In Germany, Zwick (1978) found that . Plecoptera fed preferentially on a number of stream insects other than

simuliids.

EPHEMEROPTERA

The majority of larval Ephemeroptera are not carnivorous, however, certain

Heptageniidae (Crisp, t 956a; Service and Ëlouard, 1980) and Baetidae (Crisp,

1956a; Agnew, 1962; Service and Elouard, 1980) have been reported (0 feed

mzc !jAS .. , ~-' -12- ) on SimuLiurn larvae. On the other hand, Bradt (1932) observed Simulium larvae

entangling and immobilizing small Ephemeroptera nymphs in their sllky

./secretions. Other authors have tested various Ephemeroptera nymphs and found

no evidence of them of feeding on black flies (Service and Lyle~ 19i5).

ODONATA

Goyareb and Pmger (1978) noted naiads of and Agrionidae

f eed ing on black fly larvae in Brazil. Service and Ly,le (I 975) tested Z ygonyx

flavicosta nymphs (LibeJlulidae) in the Ivory Coast and found tha t 30% reacted

positively to black fly antiserum, comparable results were later obtained by

Service and Elouard (980) for Zygonyx torrida.

DIPTERA

Despite their small size a number of dipteran larvae have been implicated

in studies of simuliid predation. Sommerman (1962) found the larvae of two

different species of Oreogoton (Empididae) feeding upon black fly larvae in

1 Alaskan streams. Grenier 094-5) observed' the larvae of Melanochela riparia

FaU•. (Anthomyiidae) attacking immature black flies under laboratory conditions.

There are several important reports of aquatic Drosophila larvae

(qrosophilidae) attacktng simuliid larvae. Tsacas and Disney (1974) discovered

two new speCles of Drosophila from the forest zone of West Cameroon which

fed mainly on the first and second instars of Slmulium. These larvae are quite

voracious, the remains of up to 140 first and second instar Simuliidae having

been identified in one Drosophila larva. The larvae of thesh- species are

considered important candidates for use as biological control agents smce they

feed selectlvely on Simulium eggs and young larvae, and Simuliidae are the

dominant item in their diet. The Drosophila pupae are parasitized quite

i -13-

extensively by a wasp of the genus Trichopria (Diaprlidae: Hymenoptera) and

it may constitute a signIflcant factor In the regulatlOn of Drosophila

populations (Tsacas and DIsney, 1974). Disney (1975) examined the" guts of the

tirst recorded aquatlc Drosophlla larva, Drosophila gibbinsi from the Nile in

Uganda, and found that this species fed preferential1y on the eggs and first

instar larvae of Simuhum.

Chironomid larvae have frequent1y been recorded as feeding on the i~ggS of

SimulÏum as weIl as the adhesive mucous which bmds the eggs together

(Grenter, 1943). There are also numerous reports of chironomids feedmg on

young Simullum (Wu, 1931; Hocking and Pickering, 1954; Peterson and [)avIes, .. . 1960). o Canni baltsm is a form of predatIOn and has been reported for Simulium'

larvae by Burton (l971) and ear lier authors cited by him. Burton (1971)

dissected large larvae ana found several small flrst Instar larvae wÙhm' their

gutSj Jaboratory observations were made of older specimens feeding upon " smaller larvae which drifted into their cephalic fans.

OTHER GROUPS.

There are records of predation on simuliids from members of other groups

tha tare not important components of the fauna associated with Simulium

larvae, but which under certain circumstances may influence black fly

populations.

Gorayeb and Pinger (1978) established that corydalid larvae in Brazil fed

extenslvely on Simuliidae when in their presence; Stewart et al., (1973)

confirmed these observatiOns with corydalids from clear rocky streams in Texas.

Aquatic Lepidoptera are rare, however, certain immature members of the

_~J subfamlly Nymphulinae (Pyralldae) occur in fast flowing waters, 7996 of those -14- tested by Gorayeb and Pinger (1978) reacted positively to 5imulium antiserum and the remains of larvae and pupal branchial tubes were found in dissected specimens.

Larvae of the famHy Dytiscidae (Coleoptera) may be found in lotie habitats and have occ~sionally been incriminated as ~'predators of Simulium larvae in temperate climates (Jones, 19~9 and 1950; Peterson, 1960), and large numbers of adult staphylinid beet1es were observed tearing simuliid larvae off rocks in o an Illinois stream (Belluck and Finnish"1981).

Hocking and Pickering (1954) observed that numerous Hydra (Hydrozoa,

C,nidaria) from northern Manitoba (Canada), accidentally introduced into black

Uy rearing bowls, quickly decimated the larvae. Specimens were subsequently

collected from the stream where the y were feeding on black fIy' larvae. Back

(1982, pers. comm.) observed large numbers of Hydra at a black fly breeding

site in the Yamaska River, Quebec.

PREOATORS1 OF BLACK FLIES IN AREAS OF ENDEMIC ONCHOCERC[ASIS.

Studies on predation of black flies which transmit oncl'lOcerciasis have

been reported, by Hynes and WiHiams (1962) in and by Crisp (1956 a,b)

who made observations and perforrned gut dissections on invertebrates

associated with Simulium damnosum Thèobald in Ghana. Service and Lyle

(1975) and later Service and Elouard (1980) determined the predatol"s of the S.

damnosum complex in the Ivory Coast, by means of the precipitin test. , Castaldi and Gutierrez (1981) studied the entomofauna associated with larval

black flies, vectors of onchocerciasis in Chiapas Province (Mexico). They

performed gut dissections of small numbers of potential predators and identified

Anacroneuria (Perlidae, P1ecoptera) as the only predator of black flies in the

regiOl1. The number of linsects' dissected other than Anacroneuria was too small,

_.. '( -15- however. to substantia te these conclus. on':..J0r a yeb and P inger (1978) studied

the-predators of Simulium fulvmotum Cerq. e Mello by means of the preclpitin o • test as weil as gut exammations. Garayeb and Wai Yin V10k (1982) compared

the efficiency of the capillary tube and Immunodiffusion precipitm tests in

determming the' predators of ~. fulvinotum. Simuliurn fulvinotum lS a cam mon

simuliid in Brazil where foci of onchocerciasis exist, however~ it has never been

cited as having any medical or veterinary importance. This study was meant

as a model for possible predator-prey interactions ln the case of medlcally

important vectors. Gorayeb and Pinger (1978) determined fiy~~ important groups Q , of predators for S. fulvinotum; Perlidae (Plecoptera) with 58.7% positive,

Chi marra (Philopotamidae, Trichoptera) with 1t1.3% positive, Macronema

(Hydropsychidae, Trichoptera) with 32.9% positive, Nymphulinae (Pyraltdae,

Lepidoptera) with 81% positive and Corydalidae (Neuroptera) with 69% posItive.

Both the Nymphulinae and the Corydalidae are groups WhlCh are not usually

found in associatlOn with black fly vectors in Afnca 50 that results for these

groups cannot be compared to the other r'ecords.

The studies by Hynes and Williams (1962) involved three groups determined

to genus: Neoperla 8%, Cheumatopsyche 396, and Hydropsyche 2%, were

diagnosed as having fed on simuliid larvae. These numbers appear remarkably

low in v iew of later studies. Service and Lyle (I 97 5) found Cheumatopsyche

W. (Hydropsychidae)' to be the most important predator in the Ivory Coast. A

more thorough study performed by Service and Elouard (1980) conflrmed this

diagnosis and Identifled the culprits to the species level: 34.% of Ch. falcifera,

2996 of Ch. digitata, 1596 of Amphipsyche, and 19% of Macronema had ~ consumed black fly larvae. Large numbers of Trichoptera were testêd and these

percentages are reliable. Only two Plecoptera were tested and neither was

positive. Although su ch a small sample size may not give any indication of the ~ r\

\

1 -16-

reality, the sample size 1s probably in direct relationship to the pumbers of

Plecoptera present which would indkate that thC"y are rare and their influence

~n the black Uy population negligible. These results conflict with those of

Crisp (l956a) who found Plecoptera to be the most important predators of

black flies in Ghana. Sorne Ephemeroptera were found to be preying on ~.

damnosum, 10.596 of Tricorythus sp. (Tricorythidae) and 22.296 of Afronurus

(Heptageniidae) reacted posltively to black fly antiserl,lm. Amongst the

Baetidae, 16% of one species of Centroptilum had consumed slmuHids. Both th~

adult and immature stages of Elmidae (Coleoptera) are usually considered to

be strictly herblvorous, yet 17.396 of Potamodytes larvae and one out of two

adults tested were positive. Amongst the Odonata 30-4096 of Zygonyx tQrrida

were declared to have preyed upon black flies. A smaU percentage of

Orthoc'Jadiinae tested were positive. This is an interesting observation since

Orthoclad1us (Orthocladiinae: Chironomidae) was introduced ta New Zealand and

Australia (Anon. 1932) to control black flies. "

INTERPRETING OreT FROM CUT ANAL YSIS. l , , Apart from direct observation in the field or under laboratory conditions,

two main techniques have been used for determining the diet of insects: visual

analysis of the gut contents and serological identification of specifie antigens in

the gut.

VISUAL ANAL YSIS OF GUT CONTENTS.

There are a variety of methods used for determining the diet of aquatic insects by examining their gut contents. The most frequently employed methods have been reviewed and discussed by Brown (I96I) and Cummins

(1973). Martin and Mackay (1982) compared the reliability of three commonly

1

~~------~------

-17-

used techniques.

Visual analysis of gut contents enables one to determine the proportion of

aU types of food such as algae, vascular plant tissue, diatoms, detritus,

prey etc. Careful gut analysis is informative but extremely time consuming. It

may lead to the underestimation of the importance of certain food categories

in the diet,' if the appropria te technique is not chosen (Martin and Mackay

19&2).

SERotOGICAt METHOD.

This technique i5 useful for determining which invertebrates have fed on

a particular prey item, it is based on the reaction of prey material from the

gut of a predator with antibodies in the blood serum of rabbits which have

been innoculated with an extract of the prey. This method has been used

frequently in the fie!d of medical entomology to determine the predators of

anthropophili!!> mosquitoes (Service, 1973 a,b,d, of the black fly ~imulium

damnosum (Service and tyle, 1975; Service and Elouard, 1980) and of the

tse-tse Uy Glossina (Boreham and Gill, 1973). For 'a review of the use of'

serology in predator-prey relationships see Boreham and Ohiagu (1978).

The advantage of the serological method is that it allows one to rapidly

process large numbers of predators and to demonstrate predation in animaIs

with piercing rnouthparts which suck up prey 'juices and whose liquid gut

contents are difficult to identify by visual examination. The limitation of this

method is that it does not indicate the number of prey consumed nor does it

provide any information on prey items other than the one being tested. This.

makes it difficult to evaluate the importance of the prey being tested

compared to other dietary components. -18-

MATERIALS ,AND METHODS

STUDY AREA

ln Southern and Western Sudan onchocerciasis occurs in locaIized foci along the numerOus rivers which run north from the great watershed situated near, the Central African Republic and Zaire. Most of these rivers eventually flow into the Bahr-el-Ghazal, one of the main tributaries of the White Nile. A. wide

\ ironstone plateau hugging the southern border of Bahr-el-Chazal Province, separates the watershed from the flat alluvial plains--,north of Wau, where water current becomes too slow for the vectors. The riverine communities of the plateau are almost aIl afflicted wit~ bllnding onchocerciasis. The study area was situated on the Bussere and Sue Rivers dose to the town of Wau where they join to form the Jur River (Fig. 1). The breeding, . sites' 0 of StmuHum larvae consist mainly of rocky bends in the rlver, and man-made causeways formed of rough ironstone rocks. Two such causeways exist on the Bussere, one at Ngohalima, which is often overgrown with Jong grasses, especially when the water level is low, and one at Bussere. On the Jur River there is a wLde causew,ay at Wau. Both Bussere and Wau causeways are similar in structure, supporting little vegetation and characterised by an irregular structure causing

the formatibn of severa! channels through which the water rushes. At the

height of the rainy season (in years of high precipitation) when the river is

runing high or overfJowing it's banks, new sites are created by the submerged

vegetation lining the river.

Wau is situated in the dry "Sudanese savannah" region. There are two

distinct seasons: the wet season which lasts from May until the end of August and the dry seasono Both the Sue and the Bussere are temporary rivers which

habitually cease fJowing îowards the end of February.

_.... f -19-

In Southern Sudan the Simulium damnosum complex is formed of two

cytotypes, Simullum damnosum sensu stnctu and Simulium sirbanum; these have

been ranked as species by Vajime and Dunbar (I975) and are grouped under the

term Sii?uliurn damnosum sensu lato, when no distinction is made between

them.

INSECT COLLECTIONS.

From 1981-1983 members of the World Health Organization (WHO) team

researching the effectiveness of localized onchocerciasis vector control in

Bahr-el-Ghazal Province, Southern Sudàn, periodical1y collected black f1y larvae

and associated fauna in the course of their inspections of the river for vector

. breeding sites. Most of the collections originated from the Bussere and Sue

Rivers near Wau. The principal collectmg sites (Fig. 2) were: Ngohallma,

Bussere Causeway, Bussere School, Agok 10 C/S, Agok Bend and Cannmg

Factory on the Bussere River and Abongara, Nyikijo and Nyiduk on the Sue.

Expeditions were also made 50 km upstream of Akanda ta Nummatina on the

Bussere River and 95 km upstream of Nyiduk to RaffHi on the Sue (Flg. 1), ta

search for possible breeding sites. Associated invertebrates were collected

simultaneously.

AlI the W"HO collections were made by hand plckmg. Sites which

appeared favorable to black fly larvae were sampled by collecting a handfull

of vegetation, leaves and branches; these were, placed in a plastic bag with

a small amount of water and kept in a shaded area of the boat and returned

to the laboratory the same day, where they were preserved. Ali these

collections were made available ta the author.

From January 1983 till August 1983 additional collections were made by

the author concentrating on the main breeding sites: Ngohalima Causeway,

-- -20-

Bussere Causeway and Wau Causeway. The tirst two sites are situated on the

Bussere River. 'Vau C!'luseway stretches across the River Jur, 6 km downstre-am

of the confluence of the Bussere and the Sue. Both quantitative and qualitative

samples were taken:

1) Quantitative samples were taken with a 15cm X 15cm Surber sampler

(' in those sites were it was possible.

2) Qualitative samples were taken by hand picking the rocks which formed

the substrate of the causeways.

Due to the fact that in May 1983 the control phase of the WHO project

was implemented, Bussere and Ngohalima causeways were sprayed weekly with

Abate~ therefore the associated collections were concentrated at Wau

Causeway where the fauna did not suffer any short term effects from the

insecticide being poured into the river 30 km upstream. The insecticide ',lias

further diluted by the waters of the Sue which merge with those of the",

Bussere 6 km upstream of \Vau Causeway.

SORTING.

ln the laboratory the samples were either processed immediately or placed

in the ref r igera tor and sorted the following morning. Each sample was

identified with the date and the name of the sampling site. Sorting was done

by hand in the lab, using a fIat b~ttomed white enamel tray into which the

( , . samples were deposited and diluted, with clean water. Very silty samples were

nnsed through a fine sieve and the invertebrates returned ta the tray. Ali the

invertebrates were preserved in 75-80% alcohol with a few drops of glycerol

per litre (to prevent hardening of the specimens and desiccation if the alcohol

evaporates).

-- -21-

IDENTIFICATION.

Samples were initially sorted to order and later identifled as far as

possible. Due to the lack of knowledge and keys for most groups of immature -- aquatic insects from the Ethiopian region, members of sorne groups could be --identtfied---- only-to-genus.-a.nQ mor~ ,rarely 'Only to family. . AlI msects suspected of being predators were separated to species and descnbed by numbers till such

time as they could be conclusively identified.

Confirmation of the determmatlons for the Odonata and the

Ephemeroptera were made by Dr. S.J. Brooks of the Bf"-itish 1\Auseum of Natural

History (S.M.N.H.), London, England. Most Tnchoptera were identifled by Dr.

P.C. Barnard (S.M.N.H.), Cheumatopsyche sp. VIII was identified with the use

of Statzner's (1984) key to the Hydropsychmae of the Ivory Coast. The

Chlronomidae were c1etermined by Dr. P.S. Craoston also of the B.M.N.H. Dr. "'\? H.P. Zwick of the Max-Plank Institute fur Limnologie in Schlitz (West Germany)

confirmed the Plecop~era and Dr. L. Landsbury of the Hope Department of

Entomology, Oxford University, Oxford, England, identified the Hemiptera. ,,'

GUT DISSEcrIONS.

Gut dissections were performed to determine the presence of animal prey

~ithin the gut$ of potential predators, and ta ident1fy the origin of the prey

and the number consumed.

The guts of 19 species (or genera when species cou Id not be determined)

were dissected out and examined for small pieces of chi tin. The specles

selected for gut dissections were those which occurred in known and accessible

breedi~g sites in the Wau area, and did not include the rare specimens

occasionally collected from potential but poorly explored breeding sites.

Specimens dlssected belonged to the following groups: Trichoptera, Plecoptera,

Odonata, Ephemeroptera and Coleoptera. The suspected predator was placed on ---- ...

-22- a glass slide, under a binoculgr microscope, the head capsule was measured as an indication of the slze, of the specimen. The entlre gut was removed' and placed in a drop of polyvinyl-lactophenol or in polyvinyl-Iactophenol + lignin pink on a glass micros.cope" slide. The digestive tube was opened and the contents were dispersed. A glass caver slip was' placed over the" entire . preparation. The lignin pink was used to stain chitin and animal tissue. Each slide was completely scanned under, the compound microscope a t a magnification of 100X. Any sclerites whose origin was not obvious at 1aax c were axamined at a magnification of 450X. AlI sc1erites and their origm were recorded. The m'inimaI number of each prey "type in the gut was estab!ished on 1'{fJ • the basis of the sclentes observed. These included claws, legs, prolegs, anal claws, he ad capsules, mandibles, eephalic fans, hypostomial teeth, proventricular teeth, elytra, cerei, antennae and eggs. A reference collection of the parts of aIl possible prey items was made by dissecting into it's component parts, a member of each group or species and placing aH the piecès into a clearing solution consisting of:

1 part 10096 acetic acid

1 part 10096 lac tic acid

2 parts distilled water

The various pieces of ehitin were then rinsed in 7096 alcohol to eliminate the dearingi-solution and prevent crystalization, and mounted individually in a drop

1. of King-'~radley-McNeil mounting solution placed on a microscope slide. This

-h solution con!31sts."Qf: ~ ~, ~"'''' -" './', ",-. • .,r / .. \

Chloral '-hydrate ZOeg···· ,'" .'" h h.' , ..- '" "1./... ./'... v .... , ./... "' .. , v~ 1 _,.., ,.., • Glycerol 20g

Gum arabic 30g

Distilled water 50ml

1 -23-

Drawings were then made of ail these parts and used as references ta identify

the origin of the pieces of chi tin found in the gut dissections (Appendix 1).

During the examination of the gut contents any unidentifiable y\t characteristic

looking pieces of chitin were drawn. It was often possible to identify the

origin of the piece la ter, in the light of further dissections. Aimost aIl prey 1

'" items couid be identified to order, most to genus and sorne ta speciesi This 1 1 depended on the degree of destruction withstood by prey in the stomach of a

1 predator. For each specimen examined, the identification and numbers of each

prey item were recorded. For each species examined, the structure and pattern

of the proventricular teeth were recorded, when present.

NUMERICAL TREA TMENT

Once the most important predators were determined, the following

information was ca1culated for each of these predators:

a) Percentage of different pre'~ items found in the gut. The hypothesis

tha t aIl prey categories occurred with equal frequency was tested (Appendix

2).

In order to determine which prey items replace SimuHum in the diet.,

of predators when black fly larvae were not availabIe, resu'lts from gut

dissections from ~pecimens that were collected from sites which did not,

harbour SimuHum Iarvae at the time of collection were analysed sepd.rately in sections a} and b). Only animais collecJted /{n-~th-è' presénce of Simulium were

considered in ail other analyses. f b) Mean number of different pfy items f~n9 in the gut. An analysis of variance was performed (Appendix~ -:3). :::: -~ ',; c) Voracity, i.e., mean""total number, of prey/individual specimen. Following

the analysis of variance, tests amongst means were carried out using the

1 1 \ '~ \

,p Î -24--

multiple comparison test: Tukey's w-procedure (Steel and Torrie, 1980), r (Appendix 4-).

d) Variation of diet composition depending on the age of the predator. Each species of predator was divided into 3 size classes, ba~ on head

measurements, large, medium, and small (Appendix 5),< for overlapping

measurements body lengt~ was also taken into account. An analysis of

"'-vanance was performed (Appendix 6).

e) Variation in diet composition depending on the season. The year was

divided into three periods of four months each corresponding to the different '.

conditions of the river (increasing discharge, spa tes and decreasing dlscharge).

These are Important factors regulating the distribution pnd diversity of aquatic insects in tropical regions (Statzner, 1982). If

() f) Percentage of specimens wlth prey, percentage of specimens containing

detritus only, and percentage of specimens with empty gtlts.

g) The relative importance of each species in reducing larval bla~k fly " popula tions was determined by the mean number of black fly larvae it

consumed. This value was corrected for predators -which were secondary

~carnivores and consumed other predators of black fly larvae by subtracting

from the number of simuliids consumed, the number of black fly larvae that

would have been' consumed by the beneficial animais it had also mgested. The.

value r:epresenting the relative importance of each predator m reducmg black

fly populations was called the ''Theoretical Index", (Ti) since it indicates those

animaIs which theoretically have the potential of exerting a great Impact on

black fly populations. -25-

Ti{x) = XSim(x) - (XB(x) x XSim/B)

where:

XSim(x) = the mean number of black flies consumed by an individual of

species x.

XB(x) = the mean number of beneficial insects consumed by an individual of

species x. The only beneficial predators that were themselves preyed upon,

were Trichoptera of the genus Cheuniatopsyche.

XSim/B is a constant, it represents the estimated mean number of black flies (-"'~ -~ consumed per Tnchbptera of the genus Cheumatopsyche and is obtained by the

? following formula:

ReI(xÙ(XSim/xl) + ReI(x2)(XSim/x2) + ••• + Rel(x4)(XSim/x4)

XSim/Ch , = \

Rel(x 1) + Rel(x2) + Rel(x3) + ReI(x4) L/

where: ReI(xl) = Relative abundance of Cheuma toeslche coeiosa ReI(x2) = Relative abundance of Cheuma toeslche digitata ReI(x3) = RelatIve abundance of Cheuma toeslche falclfera ReI(x4) = Relative abundance of Cheumatoeslche sp. VIII XSim/xl = Mean number of SlmulIum consumed per Ch. coplosa

XSim/x2 = 'v1ean number of SlmullUm consumed per Ch. digitata

XSim/x3 = Mean number of Slmulium consumed per Ch. falclfera XSim/x4 = Mean number of Slmulium consumed per Ch. sp. VIII -26-

The true impact of a species dèpends also on it's abundance, thus to obtain the

"Real index" (RD, Ti was multipHed by the relative abun<;lance of the species being considered. ---

, Ri(x) = Ti(x) x ReI(x)

where:

oRi(x) = the "Real" index' of species x Ti(x) = the ''Theoretical'' index of species x

Rel(x) = the Relative abundance of species x

..

1 ~-.- - j -27-

_ J RESULTS \

GENERAL COLLE~ON

A series of collections of invertebrates associated with larval black flie~ resulted in the identification of specimens belonging to 33 genera, 26 families, and 6 orders. A Il specimens identified and their index of occurrence are \ presented in Table 1.

GUT DISSECTIONS.

The insects dissected are listed in Table 2 (invertebrates other than insectsl were rare and consisted mainly of small bivalves). The species tha t were found to be predators (or predacious omnivores) are indicated by a fI+". Those animais in which no chitinous parts were found are indicated by a fi_fi. Not aIl of these are necessarily non-predatory, since certain predators have sucking mouthparts and only ingest thelr prey's body fluid, leaving the hard exoskeleton behind.

Those potential predators with sucking mo~thparts are prefixed by liS +/_fl.

ln sorne cases the number of specimens dissected (IIN") is very smalI, this . is due ta the fact that certain species were collected in low numbers and few' specimens were avaiIable for dissection. In othe~ cases, such as for

EJassoneuria, it was quickly determined that this insect was totally herblvorous 1 due to the consistent presence in the gut of large amounts of green vegetable

matter and the total absence of anything that was even remotely akin ta chitin. Since these observatiol)s agreed with known information about the

feeding habits of members of this group, no additional gut dissections were

performed.

The percentage of individuals of a given species which were positi've for

Simulium (i.e. in which the remains of at least one Simulium were found) are also presented in Table 2.1 have included this data since 1t 1s the main

f -28-

information which has been given in past black fly predation studies. A much

more detailed analysis of the food habits for each predator follows.

MAIN PREDATORS AS DETERMINED BY eUT DISSECTIONS.

On the basis of the gut dissections, nine important predators were

considered for further study, due either to their abundance and/or their

voracity. Insects· that were rarely carnivorous or that occurred only in very

small numbers (such as Ictinogomphus or Gomphidia) ,were not considered in the

-, study of the feeding habits, prey preferences, seasonal variation in prey and -

relative abundance, and variation of prey preferences with age, which form the

bulk of this study. The nine important predators associated with larval black

flies of the Wau area, and which feed to sorne extent on black fly larvae, are

listed on the following page. •, -29-

TRICHOPTERA ( Hydropsychidae)

Macronematinae: Amphipsyche senegalensis (Brauer)

Hydropsychinae: Cheumatopsyche digltata (Mosely)

Cheumatopsyche copiosa Kimmins

Cheumatopsyche falcifera (Ulmer)

Cheumatopsyche sp. VIII

PLECOPTERA (Perhdae)

Neoperla sp. (possibly two species, one of WhlCh

i5 Neoperla needhaml Lestage)

ODONAT A (Gomphidae)

Paragomphus or Crenlgomphus sp.

(Libellulidae)

Zygonyx sp.

Olpogastra sp.

.... ~- f -30-

DETERMINATION OF PREY

The prey items (I am referring to animal prey exc1usively) were divided into five categories of prey which were identifiable by means of the gut dissections. The number of, prey items trom each category was recorded for each predator dissected. Any small particulate matter which was not of animal origin (i.e., was not stained by lignin pink) is referred to as "detritus" throughout the texte

The first category is "Simulium": prey items belonging to the genus

Simulium were easily identified by means of their mandibles, hypostomial teeth, cephalic fans (whole fans or single rays), anal hooks and sclerites and occasionally entire head capsules. AIl identifiable parts were recorded for each dissection, thus enabling me to determine the minimum number of h1ack fly larvae consumed. For example a specimen found to contain 3 mandibles, 2 complete anal sc1erites and numerous rays of cephalic fan was recorded as having fed on two Simulium larvae. It was frequently 'possible to identify the

Simulium to species, especially ~. damnosum, due to it's large number of rows' of anal hooks, characteristic hypostomial teeth and particular flattened scale-like setae, and ~. griseicolle, due to it's characteristic mandibles with only one serration instead of the usual two found on the other species of

Simuliidae encountered in Southern Sudan (Crosskey, 1960), see Appendix '1.

The second category is "Trichoptera": it was in 'general easy to differentiate between members of the genus Cheumatopsyche and other

Trichoptera. Cheumatopsyche are the main trichopteran predators, ail of them partial to~ Simulium larvae. It was important to be able to distinguish between the mean number of Cheumatopsyche (i.e., beneficial Trichoptera) and the mean number of other non beneficial Trichoptera consumed by a given predator. For /

-31-

example, if a predator consumes a small number of black fly larvae and many

times more Cheumatopsyche larvae,' it cou Id have a net boosting effect on the , ) black Uy population py killing off their main enemies. On the other hand, if it \\ consumed the same nu~.nber of Trichoptera, but ,these were not Cheumatopsyche,

it would maintain it's controlling effect on black fly populatiofls.

The third category' is the "Ephemeroptera": the~e can be recognized by -- their charactedstic mandibles, claws and pieces of Jeg {Appendix O.

The fourth category is the "Chironomidae", which are identified by means

of their head capsules, anal claws and prolegs.

The last category is t~rmed "Others": it inc1udes various prey items such

as mites, tiny bllf.alves, eggs, beetles etc., whictl are not common prey items. 1 Unidentified prey were also placed in This category.

DIET COMPOSmON '.

PERCENTAGE -GF DIFFERENT PREY ITEMS IN GUT. , 'The percentage of different prey items that compose' the carnivorous diet

of the nine predators are shown by a se~ies of pie charts (Fig. 3) placed in

order of decreasing percentage of Simulium consumed. Thus, Zygonyx (Fig. 3a)

is the predator which has the highest percentage of Simulium in it's diet,since

the y form 54% of the total number of prey items consumed. The predator

which consumes the smallest percentage of Simulium is Amphipsyche

senegalensis (Fig. 30, with black flies composing only 396 of it's prey.

1\he percentage composition of different prey items in the diet of various

predators Ïs interesting since it may reveal a predator's preferred prey. :ffills,

Zygonyx and Ch. digitata prefer Simuliidae. Paragomphus or Crenigomphus and

Neoperla pre fer Chironomidaej .Q:!. falcifera and Ch. copiosa fed more or less -32- equally on Chironomidae, Simuliidae and Ephemeroptera. Cheumatopsyche sp.

, vm and Amphipsyche senegalensis prefer Ephemeroptera and Olpogastra is most

partial! to Trichoptera larvae.

Variation in diet composition of animaIs collected in the presence and absence of Simulium larvae showed that for Ch. copiosa and Ch. digitata,

Chironomidae largely replaced black fly larvae when these latter were not

available (Fig. 4).

MEAN NUMBERS OF PREY CONSUMED PER PREDA TOR.

If one is interested in the importance of various predators in reducing the , population of a specific prey category, such as Simulium, the mean number of " prey items consumed per predator is a much· more reveaIing indication of the

actuaJ impact of the various predators on the prey population (Fig. 5). The

mean number of prey per predator takes into account the voracity (or degree

of carnivory) of the predator. For example, Simulium comprised 30% of the

animal diet of Q. copiosa and only 1696 of that of Cheumatopsyche sp. VIII;

yet Cheumatopsyche sp. VIII had a mean number of 0.62 Simulium larvae per

individual predator compared to 0.26 for Ch. copiosa. Despi te the tact tha t ~ Simulium comprised almost twice as much of the animal, diet of Ch. copiosa

than of Cheumatopsyche sp. -VIII, if these animais were present in equal

numbers, the impact of Cheumatopsyche sp. VIII would be two and a half times

greater than that of Ch. copiosa.

Table 3 con tains the voracity values (i.e., mean number of prey per

preda tor), percentages of specimens which had fed exclusively on detritus

and/or vegetable matter and percentage of ar:timals with empty guts.

-- t -33-

COMPARATIVE IMPORTANCE OF DIFFERENT PREDATORS.

By~. taking Into account the mean number of Slmullum consumed per

predator, as weH as the mean number of Slmulium that would have been eaten "'" by the beneficial Trichoptera aiso consumed by the same predator, one can . 'obtain an index of relative importance of each pret:lator. Figure 6 mdicates the

re lative importance of the nine dlfferen.t predators m controllmg black fly

populations, assuming they are present in egual numbers. l have called these values "Ti" (Ti = theoretical index), In theory the most Important benefJcJal predators affecting black fly larvae ln breeding sItes of Southern Sudan are (Ln order of decreasing importance): Zygonyx (Ti=1.62), Neoperla (Ti=O.77),

Cheumatopsyche sp. VIII (Ti=O.62), Ch. digltata (Ti=0.53), Paragomphus or

Cremgomphus (Ti=O.27), Ch. copiosa (Ti=O.25), Ch. falclfera (Ti=O.22) Olpogastra

(Ti=O.13), and Amphlpsyche senegalensls (ThO.Ol)

The actual importance of these predators ln the fjeld, however, 15 gUlte different, since many of the (theoretically) most effective predators are present in very small numbers. By muItlplymg the ''Tl'' of each predator by It's relatlve abundance, one obtams a new series of mdlces: "Ri" (Ri = real Index), mdlCatmg the actual importance of different predators In reducmg black fly' populations

(Fig. 7). Thus, in ·reahty, the species exertmg the greatest pressure on larval black fly populations are (in order of decreasmg importance): Ch. dlgltata

(Rl=229.49), Ch. copiosa (Ri:: 118), Zygonyx (RI=57.05), Neoperla (Rl=33.1l), Ch.

1 falclfera (Ri=25.52), Cheu~atopsyche sp. vni (Ri= 14.26), Paragomphus or

Crenigomphus (Ri=6.2l), AmphlpSyche senegalensis (RI=I.25) and Olpogastra

(Ri= 1.11).

The mdlèes "Ti" and "Ri" are values which may only be compared between themselves (t.e., '71'" with "TI" and "Ri" wlth "Ri"). These values do not correspond ta a numertcal measure in the field; an insect 'wlth a "TI" of 0.6

l -34-

would have twice as much effect (theûretically) on the black fly population, as

one with a "Ti" of 0.3. ln the Wau area, for example, an insect with a "Ri"

of 200 has twice the importance as a black fly predator, as an insect having

a "Ri" of 100.

VARIATION OF DIET WITH AGE.

The variation of diet composition in ter ms of mean number of different

prey items per size class per predator is illustrated in Figure 8. The , voracity values for each size class, as weIl as the percentage of animais

feeding on detritus or vegetable matter only,are listed in Table 4.As would be

expected the voraclty of most species increased as their size increased and the

smaller sizes fed more frequent.ly on detritus and vegetable matter only,

indicating that they were less carnivorous.

SEASONAL DISTRIBlITION OF PREDATORS. d Although most of th~ samples taken were not quantitative, each sample

consisted of one or more stones or handfuHs of vegetation and all the insects \ pesent were recorded. Thus, the relative abundance of different insects may be

compared, since none were collected selectively. It is impossible ta us~ total

numbers per season as an indication of seasonal ,variation" since the number of

samples collected varied greatly at dlfferent times of the year. It is

acr.eptable, however, to calculate the percentage of representation of each

species within the predatory fauna, thus demonstrating seasonal shifts in

relative importance of different predators. The year was divided into three

seasons of four months each, corresponding to different conditions of the river

as recorded by Baker (984) du ring the three years of collection. Period 1

ranged from the first of April to the end of July, this corresponds to a time

l - -35-

of mcreasing discharge. Period 2 ranged trom the beginnlng of August to the

end of November and corresponds to the period of high water or spates. The

third period ranged from the first of December ta the end of March and

corresponds to a time of decreasing discharge until complete cessation of flow

~,this usually occurs sometime in F ebruary or March). In 1981 the flow,

, however, never stopped (Baker, 1984-). The percentage composition of aIl the

members of the predatory fauna reflect the relative importance of each speCles

duri~~ different seasons and is 111ustrated in Figure 9. Cheumatopsyche dlgitata

comprised 2796 of the predatory fauna during the period of mcreasmg dlscharge,

and 60% of the f<;luna dunng the period of decreasmg water flow, with a low

of 18% during the spates. Cheumatopsyche copiosa on the other hand

comprised 51.596 of the fauna durmg the period of mcreasmg discharge, dipped

sllghtly to 4-696 during the spa tes and then crashed to only 15% dunng the

period of decreasing flow. Neoperla showed a trend exactly opposite ta that

of Ch. digitata; it compnsed only 0.32% of the predatory fauna durmg the

penod of increasmg discharge, peaked at 15% during the spates and then

dec!ined ta 2.3% dur mg the penod of decreasmg dlscharge.

t ! -36-

DISCUSSION

GENERAL" COMMENTS.

The main goals of my research were:

a) To identHy the most important predators of Slmulium damnosum 5.1. and other SimuIium species in ,the Wau area.

b) To describe th~ir selectlOn of prey items and \prey preferences. Whilst performing this research 1 also determined the variation of camivory with age; the change of relative abundance of different predators , depending on the conditions of the river; which insects are potentiaIly .' important predators and which insects exert the 'greatest pressure on larval black f1y populations under field conditlOns. 1 also determined the alternative prey choices 10 the absence of Slmulium for the two most important black fly predators.

1 shall discuss these points, examming mitial1y traits common to certam \ groups, and subsequently individual species. Where applicable, 1 shall treat concepts such as inter- and intra-specific competition and the co-existance of c10sely related species in apparently limited niches. 1 shaH compare the information obtained on the ecology of these predators with available information on members of the same species from black fly breeding sites in

West Africa.

, , , , Martin and Mackay (1982) sho,wed that the estimation of numbers of prey consumed by recording the sc1erites present can lead to gross underestlmation of the degree of carnivory. This underestimation occurred in the case of predators who did not feed on the entlre body of their prey but excavated fleshy tissue leaving behind the strongly scIerotlzed head capsules and legs.

1 -37-

The large number of head capsules, pieces of legs and claws found in the

guts of the nine species of predators examined in this study indlcates that the~

generally ingested the entire prey.

Martin and Mackay (I982) hypothesized that the "excavat1ng" feeding

behaviour of the rhyacophiIid they studied was related to it's small head'

capsule and to H's lack of a proventriculus which would have aided ln

processing hard food part1cles. AIl the Trichoptera, Plecoptera, and Odonata

examined in this sud y had a distinct proventriculus with a weIl sclerotized

armature.

The fact that the mounts' were stained with lignin pink made lt easy ta ',- spot small pieces of chi tin such as cuticular setae, whose origm could often b,e

determined under hlgh magmfication. This increased the accuracy of the

examinations.

It 1s important to remember that the number of prey recorded in each

gut represents the minimal number of prey items present. It is likely that

some items were not detected and that the bias may be against a speclfie ~rey

item whose presence is particularily difflcult to detect.

TRICHOPTERA

HYDROPSYCHIDAE.

The Trichoptera are weil represented amongst the insect fauna associated /1 .. ~ with larval black fl1es. The most important predators belong to the family

, Hydr9P,sychidae, a group formed of members with varymg food habit~, ranging

, ". , < , \ \ l , \ from detritivore/herÙ~,àr'e's; feediT'lg o,n, pne organic particles and àlgal cells" to \ , , , \ , < , carnivores, preying on whole animaIs (Wigglns, 1977). The Hydropsychldae are

represented ln the Wau area by six species belonging to three gener~ and two / \. -38-

'subfamilies: Cheumatopsyche digitata, Ch. copiosa, Ch. falcifera, Ch. sp. VIII

(s.f. Hydropsychinae), and Amphipsyche senegalensis and Aethaloptera dispar

(s.f. Macronematinae). Members of the 'Macronematinae were omnivorous

(Amphipsyche) or totally non-predatory (Aethaloptera). Ali the Hydropsychinae

from Wau belonged to the genus Cheumatopsyche and were larg~ly carOlVOrOUSj'

this concur~ with Scott's (1983) description of Cheumatopsyche from souJ,Rern

Africa as predacious omnivores. Crisp (l956a) noted -Cheumatopsyche to be

c10sely associated with the larvae of black flies in Ghana, but stated that the y ., fed exclusively on algae. Other members of the genus Cheumatopsyche are ,', .. considered to be passive filter feeders (Williams and Hynes, 1973). As shown by

'the variations in known feeding habits for members of the genus

III Oleumatopsyche ,it is imperative to identify potential predators to the species

level before mqking generalizations about their feedmg habits. It is, however,

possible to isolate characteristic trends for each species.

Members of the genus Cheumatopsyche w~re particular;ily abundant and held p '~, , a dominant position within the benthic community, composing between 7296 and

87% of the predatory populatIOn, depending on the season. High densities were

also obtained for Cheumatopsyche by Gibbs (J973), Hynes (1975) and Statzner 1 (I982). Oleumatopsyche.

The taxonomy of the West African Cheumatopsyche has recently' been

elucidated by Statzner (I984). In his clear and weIl illustrated key to the

Hydropsychinae of the Ivory Coast, he describes this group as being segregated

ioto three main distribution areas: the mountainous region, the non-mountainous

f,orest region, and the savannah region. The four species of Cheumatopsyche

collected froln Wau belong to the sava,nnah regil rroup• The apparent

,1

indicates that there may be grounds for extending information obtained on predators of S!muliidae in Wau to the Sudan savannah regions of West Africa.

Cheumatopsyche digitata.

Cheumatopsyche digitata is the most important predator of l~rval black f lies in the Wau area (FIg. 6). It exerts a depressing effect on larval populations due to severa! factors:

a) it's preference for SimuIium larvae above other for ms of prey;

Simulium constitute 35% of the total number of prey items consumed;

b) it's high voracity; (double that of Ch. copiosa ,nd Ch. falcifera) (Table

2);

cl i t's abundance; 1t 1S the second most abundant trichopteran, Ch. copiosa being the most abundant.

Cheumatopsyche digitata occurs simultaneously with Ch. copiosa, they

were frequently collected together on, the same substrate, and since they have

similar feeding habits, one would expect sorne form of competitio!",

Competition.

Competition and territoriality are weIl documented phenomena among the

Hydropsychidae. The stridulatory ridges on the ventral surface of the head and

a 'scraper on the femora of the front legs are used in sound production (for

illustration cf. Johnstone, 1964). Glass and Bo~bjerg (1969) demonstrated that -40-

Cheumatopsyche larvae display agressive behaviour and spacing ln nature and ln the laboratory, and that the presence of refuges allows the co-exlstence of higher densitles of larvae. This was certamly the case ln \Vau where the rough ironstone substrate formed numerous natural refuges and enabled high numbers " of Cheu ma topsyche larvae to co-exist. They also showed that certain species were more effective at defending their territory than others. J'ansson and

Vuoristo (I979) showed that stridulation was used in both inter- and lntra-speclfic behaviour: and that those caddisfly larvae which stridulated were more successful in defending thelr retreat. The Cheumatopsyche from Wau were active predators and it would be interesting ta determine whether the y only defend the refu~e or also an area around the refuge which cou Id be considered as hunting grounds. This could only be determined by patient labora tory observations, the river water being too turbid to allow field observations. When a rock was hfted out of the water; members of the same species of Cheumatopsyche as weil as other Cheumatopsyche were found in

\ dose proximity, giving the impression that they did not establish distinct areas of activity. The conditions of these observations were, however, quite disturbing since the substrate was puIled· out of a dark cool world of flowing water into the bright warm sunlight j it i5 Iikely that the behaviour of these animais wa~ atypical.

DJe to the sporadic supply of electricity in Wau during the time of these collections it was impossible to establish an aquarium which was aerated weIl -~ enough to maintain stream insects alive.

Although Ch. digitata and Ch. copiosa occurred simultaneously, Ch. copiosa was dominant during the period of increasing discharge and during the spates (April to. November), and Ch. digitata was dominant during the period of decreasing flow (December to March), (~ïg. 8). Thus, though they share similar niches the temporal spacing could be an import~~~ in redLJctng

inter-specifie competition ( for a discussiOn on tlme as a niche dlfference, see

Carothers and Jaskiè, 1984). ft is probable that this temporal shifting of thelr

lite cycles is related to the period when thelr functioning is. optimal; Ch. 1 dig1tat: functioning better in periods of deereasing water flow and Ch. copiosa

in periods of increasing discharge and hlgh water levels.'

Cannibalism.

A high number of Cheumatopsyche remains were recovered from Ch.

digitata larvae: a mean number of 0.11 compared to values rangmg from a to 0.02 for other Cheuma topsyche, (F ig. 5). ThIS is surprising and lmplies tha t sorne. of these may be Cheumatopsyche digitata, i.e., that it is cannibal1stlc. The

·canniballstic nature of Cheumatopsyehe dlgltata has already been postulated by

~tatzner (I982) and Elouard (1983); neither found smaH and large Ch. dlgltata'

"')-Jarvae on the same substrate. The high level of Cheumatopsyche remams from

Ch. digitata further supports these observations.

, -. Cheumatopsyche copiosa.

Cheumatopsyche coplosa is the most common species of Tnchoptera '" occurring in the Wau area. Live, it is easily distingUlshed from other

Cheumatopsyche larvae by it's particularily bright green colouratlon. Ch.

copiosa appears to be a much less important consumer of Simullldae (0.26

\ Slmuliidae/specimenj ~ompared to Ch. 'f!igltata (0.54 Slmulildae/specimen).

Another difference in the feeding habits ~ two specles is thelr voraclty:

Ch. digltata havihg a voracity O.e., mean number of prey items/specimen)

almost double that of Ch. copiosa (Table 3). Although thlS dlfference was not

Signifjcant at the 0.05 level, further tndication of the greater carnlvory of Ch.

1 -42- digltata IS given by the percentage of ~peclmens found with prey in the gut:

7~96 for Ch. dlgltata, compared ta 56% for Ch. coplOsa. Another mterestlng

l, observation for Ch. coplOsa was that the pleces of chltln found ln the gut were

general 1Y smaller and harder ta recognlze than ln the other Cheumatopsyche.

The proventrlcular teeth (gastrlc rn ill) of Ch. copiOsa are very dlstfnctlve (Baon,

1984),and thls could account for the more effective trituration of the food. A correlatIOn between efflcacy of trituratIOn and proventrlcuJar tooth structure

has been reported by Judd (t 948) ln orthopterold lnsects.

Cheumatopsyche fà.lcifera.

Cheumatopsyche fa1cifera and Ch. coplOsa have feedmg habits WhlCh are "" virtuaJly IdentlCal (Fig. 3 &: 5). TI,e simllanty of these two specles and the

fact that they occur slmultaneously suggests thaYt~e must be sorne form of competition occurrtng between them. Cheumatopsyche falclfera conslstently occurs ln low numbers, compnsmg between 6% and 9% of the predatory fauna, whereas Ch. coplOsa compnses 5196 ln the pertod of mcreasmg discharge, 46% durlng the spates, and 15% during the penod of decrJasmg dlscharge when lt

15 replaced by Ch. dlgltata. The dominance of Ch. coplosa mdlcates that It IS generall y much more successful than Ch. falcifera, under the partlCular conditiOns ln the Wau area. ThIS dominance has not been observed in other

Sites. On the contrary, Statzner (1982) found Ch. falclfera to be dommant over

Ch. coplosa ln severa! sites 'on the 1\1'ZI River (Ivory Coast) except in the months imrnediately preceedmg cessatIon of water flow. Cheumatopsyche dlgltata and Ch. falclfera were the most Important speCies of Hydropsychidae assoclated wlth ? damnosum ln the [vary Coast, whereas Ln Wau Ch. dlgltata and Ch. copiOsa were the dommant Tnchoptera. One Important difference between the '\1'21 ([vary Coast) and the )ur (Southern Sudan) Rlvers 15 the type of substrate. The extremely' !rregular and deeply crevlced Ironstone substrate

f -43- of \Vau did not occur in the N'Zi River where rocks were described in most si tes as smooth, and in some sites as rough (Statzner, 1982). Other factors , influencing the success of 'larious species cou Id be water velocity, turbidity and chemistry, shading, substrate cover (moss, algae), food availability, etc. These .. ~ differences in corn munit y structure may also be. ,determined by limiting factors affecting the adult populations. Unfortunately there is virtually no ecological information available on the adult stages of tropical Hydropsychidae.

Cheumatopsyche sp. VIII.

" Cheumatopsyche sp. VIII" is an extremely intèresting species, due te;> itl 5 great voracity (3.86), higher even than that of the Odonata and the Plecopt'era, and significantly different at the 0.05 level from the other Cheumatopsyche.

Although it's preferred prey was Ephemeroptera, it consumed a high number of ~

Slmuliidae (0.62 SimuIiidae/specimen) (Fig. 5). This difference in diet, i.e., - the high rate of carnivcry , may be Icorrelated ta a marked difference in

the pattern and size of it's proventicular teeth, which were much smaller than

those of the other Cheumatopsyche from Wau (Appendix 7), and than those of

other Hydropsychidae recorded by Boon (1984), except for Ch. albomaculata.

Cheumatopsyche sp. VIII and Ch. albomaculata. appear to be closely related

by their external larval characters and isolated tram other Cheumatopsyche

(Statzner, 1981). Cheumatopsyche albomaculata and Ch. sp. VIll are likely

part of a group of Cheumatopsyche separa te from the other Cneumatopsyche

collected in Wau. The fact that the proventricular armature of both Ch.

albomaculata and Ch. sp. VIII are similar, consisting of Iittle more than

reduced spines, and very different from the large multi-spined teeth of the,

other Cheumatopsyche further supports the segregation of these two species

into a separate group. On the basis of external characteristics Statzner (1984) .' ) -44-

" recognized groups within Cheumatopsyche larvae, wh{ch would justify the establishment of genera and states that "this has not yet been done due ta

insufficient correlations of larvae with adults".

Proventricular teeth have frequently been used ln the taxonomy and

phylogeny of various groups: Judd (I948) and Muralirangan and Ananthakrishnan

(1974) for the Orthoptera; Balfour-Browne (1944) for the Coleoptera; Higgins

(l90l) for the Odonata; and Baon (1984) for the Trichoptera. Gangwere (1965)

and Muralirangan and Ananthaknshnan (1974) postulated a correlation between

the nature of the food qnd the specializatlOn of the fore-gut armature. It

would be interesting to study the feedlng habits of Ch. albomaculata, ta

determine wh ether the. reduction of proventricular teeth.)n this species is, also

associated with increased carn Ivory. Weil developed proventricular tee,th are

considered by certain authors (Baon, 1984) to be an adaptation for crushmg

1 dia toms and dinoflageltates. Ilalfour-Browne (1944) observed wel1 developed

proventriculi in al1 mandibulate lnsects whlch fed on hard and indigestible

matter. Gangwere (1965) observed that certain carnivorous Orthoptera 'were

characterized by partial 105s of the proventncuJar armature and hypothesized

that this was made possible by the semi-fluid dlet. Insect nymphs and larvae

are the main dlet of Ch. sp. VIII. and the reduction in proventricular teeth

in this species may perhaps be explained by the same hypothesis.

The distribution of Ch. sp. VIII is very pecuhar. It was found only at

one site in the Ivory Coast despite extensive collections (Statzner, 1982). Tt is

also known from one site in Burkina Faso (formerly Upper Volta) and now ,from

Wau in Southern Sudan. No information 15 available ln the hterature on the

densitles of Ch. sp. VIII larvae' when they were encount~red. In Wau they were

rare. Due to their great potentlal as black fly predators, It would be '-45-

useful to determine its Ilmlting factors, with the hope of being able to modify

the habitat to favour its presence and activity. l '

Amphipsyche senegalensis.

Amphipsyche senegalensis is a predacious omnivore with a voracity

comparable to that of Ch. copiosa, Ch. digitata, and Ch. falcifera, but it

dîffers from these species by rarely feeding ,on Simulium larvae (Jess than 396

of the animais observed had fed on Simulium) (Table 2), and it feeds

preferentially on Chironomidae (Fig. 3i). The level of predatIOn of A.

" senegalensis on Simulium larvae observed in this study 15 low compared to

values obtained by Service and Elouard (1980) on specimens ot Amphîpsyche

from the Ivory Coast, where approximately 17% of the A mphipsyche spp. tested

reacted positively to~. damnosum antiserum. The msects th,ey tested were not

identified to the the specles level; only two specle; have been' recorded from

the Ivory Coast, A. berneri and A. senegalensis. Amphipsyche senegalensis is'

a savannah specîes tha't also occurs in th~ forest-savannah transition' zone, A.

bernera is a forest .species whlch is also often found in the tra,[lsition zone_

(Statzner and Gibon, 1984). Since the_collections made by Service and Elouard

(1980) were from the Marahoué River, near Bouaflé, in the transition zone, it

is imJX>SSihle to hypothesize which of th~e speci~ was (or were) being tested.

The lower predation rate on Simulium larv~bserved in Amphi,Psyche from

Southem Sudan versus Amphipsyche trom the Ivory Coast, could be due to any

combinat ion of the following factors:

a) different species were examined;

b) variation in feeding habits of specimens from different habitats;

c) an increased number of positive reactions to 5. damnosum

antigens in those observations made with the 'precipitin test due to' -46-

Amphipsyche larvae scavengmg on dead 5rmulium or feeding on anrmals whrch A had themselves preyed upon Srmulrum;

d) vanation 'In the detectlOn time for the two tests; it i5 possible that the

precipitrn test is more "sensrtrve" and detects the presence of Simulrum remains

long after ail chitinous parts have been evacuated. If this were the case,

.however, one would expect observations made with the precrpitin test in other

species to show hrgher leve ls of predation, and this did not occur.

Aethaloptera dispar.

Few speCImens of Aethaloptera dispar were collected, and only Il were

dissected, none of tbese showed any signs of carnivory. It is drfftcult to form

any conclUSiOns about this species- based on 50 few observatrons, especlally since . . these records are in drsagreement with ~tudies by SerVIce and Elouard (1980)

who found that 19% of Ae. dispar testeq reacted positively to Slmuliurn

antiserum. Certamly in Wau, whether it is carnrvorous or not, Ae. dispar does

not c';ntribute significantly to the benthic community Ide due to It'5 rarity.

ThIS is an interesting point to note since in certain habitats, Ae. dispar is

considered to be an Important element of the fauna associated wrth larval

black flIes. Statzner (I982) observed that Ae. dispar encouraged the colomzation

of the substrate by Cheumatopsyche spp. by altering the habitat with rt's tubes.

Cheutna~opsyche larvae construct their ne~~between those of Ae. dispar. In

the Ivory Coast, low numbers of Chel,lmatopsyche spp. were correlated to the

disappearance of Ae. dispar from ,a temporary stream after a' period . of

insecticide treatment (Statzner, 1982). Statzner hypothesized that Ae. dispar

ameliorated the habitat for Cheumatopsyche spp. by altering the microc,:!rrent5

and the substrate surface. In \Vau this interdependence did not eXlst. Large

numbers of Cheumatopsyche spp:. were frequently found despite the absence of -47-

Ae. dispar. 1 think that the key raIe of t!=... ~ m thiS rèlationship mIgh't

not have been the modificatIon of mlcrocurrents 50 rnuch as the fashlOmng of

numerous new refuges for the Cheumatopsyche, reducmg the expreSSIon of

territorial agressiveness and al10wing them to, co-exist ln greater numbers.. The \ rough ironstone substrate characteristlc of the Wau breeding sites already

.. ' provided a hast of natural refuges.

These observations emphasize the Importance of the whole communlty

stucture when evaJuating the effect of larvicides. Although Ae. dispar IS not

considered an important predator of larval black fiies, It's presence is

indispensable tq- the colonizatlOn of certain sItes, by other more important

predators such as the Cheumatopsyche. Thus, the use of an insecticide such as

O1lorphoxim, whieh elimmated Ae. dlspar populations, IS indirectly detrtmental

ta Cheumatopsythe spp. as weil; despite the fact Cheumatopsyche was able ta

reinvade the habitat, it could not successfuUy re-establish itself due ta the disappearance of -Ae. dispar ,which was unable ta relnvade the '\SIte.

TRICHOPTERA OTHER THAN HYDROPSYCHIDAE.

\ . , Oümana (Philopotamidaé).....

Chimarra was very common, and the dominant trichopteran durtng July

at' whieh time many different instars were simultaneously present, indicating

little inter-specifie agressiveness. Chi marra spp. have been recorded by Service

and Elouard (1980) and Elouard (1983) as occasional predators of black fly

larvae, but were not considered important compared to the Hydropsychidae.

Thirty eight specimens tram Wau were dissected and no evidence of predation

was found in any of these specimens. The only piece of chitm discovered was

a minute c1aw, which most probably had drifted mto the msect's net and was

l engulfed wlth the rest of the fIltered matena1. When a gut dissection presents

eVldence of predation, It IS 'rare ta fmd only one plece of chitlnj usually

severdl fragments are present, and together they conflrm the presence of a

particular prey. The guts of Chi marra specimens from Wau were consistently

full of very fine brownish detritus, which confirms their fIlter feeding habits.

Members· of the family Philopotamldae are known ta fil ter feed on fine

particulate orgamc matter. They build remarkably deltcate silk nets wlth tmy

openings and the larva feeds by cleaning the minute particles from the net

with it's speciahzed membranous labrum (Wiggms, 1977). Coffman et al. (1971)

recorded sm aIl amounts of anima!, components in the diet of ChI marra spp. from North America; these were probably the result of prey dnfting. mto It's net. In a labo rat ory study conducted on predators of black fly larvae m

Ghana, Burton and McRae (l972T dld -not observe Chimarra spp. feedmg on

black fly larvae even if these were held close ta the net openmg; in one case only was a Simulium Iarvae attacked under such circumstances. The taxonomy

of tropical Philopotamidae is' still In it's infancy, and few larval Chimarra can

be identiHed to the species level: this explains the variations in 'observations about their feeding habits. Certainly the Chi marra spp. occurrmg ln Wau are not noteworthy predators,although they are at times important members of the invertebrate communi ty.

Hydroptilidae.

Very few Hydtoptilidae were collected and only one specimen was dissected (Table 1). These are minute micro-Trichoptera, and the dissection dld not reveal predatory habits. It was impossible to Identify the specimen beyond the famIly level. Other Hydroptilidae found associated wi th Slmullum larvae in West Africa have been members of the genus Orthotrichla. They were -49-

mitially thought to be aigal/dlatorn feeders, but have smce been recorded as

feeding upon Simuhum pupae (Burton and \kR.ae, 1972) and eggs (DIsney, 1973).

Their mouthparts are adapted for suckmg flUids 50 that It would be Impossible

tQ determine predation by means of gut dlssectlOns. In Wau, Hydroptll1dae

were 50 rare that even If they were preytng upon eggs and pupae thelr effect

on black fly populations would be negllglble.

Oecetis (Leptoceridae).

Larvae of Oecetls spp. are mmute and were rarely encountered. Four

specimens were dissected and of these, two had preyed upon Chlronomldae

larvae. rv1embers of thlS genus have long bladehke mandlbles WhlCh Identlfy

o them as predators (WIggms, 1977). They have been conflrmed as predators m

'Iorth Amenca (Wmterbourne 1971) and ln the Ivory Coast (Service and Elouard

t 980), wh~re two out of six speCImens tested reacted posltlvely to black fly

antlserum.

AN EPILOGUE TC THE TRICHOPTERA.

The results of my studies conflrmed that Tnchoptera are the most

Important predators of larval Slmulildae ln Southern Sudan; thls IS 'ln agreement

Wlth other studles f?erformed ln West Afnca. The most Important predators are the Cheumatopsyche spp. (Hydrop5ychtnae, Hydropsychldaeh members o~ the subfamlly Macronemattnae (Hydrop5ychldae) were of mlnor Importance. The J t.ligh status of Cheumatopsyche spp. as Simuliurn predators 15 due to thelr voraClty, the predilectIOn 1of certam mernbers of the genus for black fly larvae above other prey, and most Importantly to thelr I-llgh densitles. Ch. dlgltata and- Ch. coplOsa were the dommant specles wlthm the commumty and also the\ most Important predators of Slmullum larvae. -50-

Certain authors have suggested that the Cheumatopsyche feed only on

drifting animaIs, possibly already doomed. The Cheumatopsyche from Wau

appeared to be active predators. This observation is further supported by the

high numbers of black fly larvae found in their guts which indicated that they

were more than passive predators feeding only on prey which accidently drifted

into their nets. Statzner (1982) observed that only 10% of Cheumatopsyche buiIt

nets on the rocky substrate of the N'Zi R. (Ivory Coast) and 1 made

similar observations in Wau: this supports the evidence that these Trichoptera

are active predators and are not dependent on net catches for their survival.,

PLECOPTERA.

AIl the ~Plecoptera found in Wau belonged ta the genus Neoperla.

Imma ture nymphs could only pe id~ntified to genus, but mature nymphs cou Id

be identified to species. The presence of Neoperla needhami Lestage was

determined, and at least one or perhaps two other species of Neoperla werè

present in the material collected. As the guts of matUrt' nymphs were empty,'

they were not dissected, thus aIl dissected material is referred to as Neoperla. " spp. P lecoptera nymphs were most important during the period of spates and

decreasing water levels and were ra rel y collected at other times. Ne6perla . are members of the family Perlidae, the nymphs of which are usually

carnivorous (Jewett, 1959). The Neoperla f~om Wau were strictly carnivorous:

83% were found with animal matter in their guts and the other 16.5% had

empty guts. Not one specimen was found with detritus only. The high number

,'P,' of specimens with empty guts is char1teristic' of carnivorous species ~hich often feed less regularly than herbivores or detritivores who benefit from a

constant food supply. Black fly larvae were the second favorite food source

of Neoperla spp., chironomids being their preferred prey. Due to their high -51-

voracity (a mean of 3.49 prey items/specimen), they ate a large number of

black fly larvae (0.91 Simuliidae/specimen), (Fig. 5). If aIl preda~ors were

present in equal numbers, NeoperIa would be the second most important

predator affecting larval black fly populations (Fig. 6), ahead of the

Trichoptera. In actua1 importance, they rank four th behind the two most

important Trichoptera, Ch. digitata and Ch. copi osa, and the odonate Zygonyx

sp. (Fig. 7). This is because they occur in low densities. Their beneficial effect 1 was further reduced due to their consumption of a relatively large number of • Cheumatopsyche Iarvae (an average of 0.28 Cheumatopsyche per specimen

dissected), which are themselves predators- of black fiies; this was taken into

account in Figures 6 and 7. Wherever Plecoptera nymphs are found in the

presence of Simuliidae, they are considered to be important predators of their

. larvae (Crisp, 1956a; Cast9-Jdi and Gutierre~ 1981; Gorayeb and Pinger, 1978).

Plecoptera have been conspicuously uncornmon in recent studles performed in

West Africa. Service and Lyle (1975) examined a single specimen which

reacted negatively to ~. damnosum antiserum, and Service and Elouard (1980) 1 , / tested a total of three Plecoptera, alt/tlf which reacted negatively. Twenty / nine percent of the Plecopter:-a from Wau had fed on at least one Simulium

larva. While performing the gut dissections of Neoperla nymphs 1 observed that

if the remains of one black fly larva were encountered in a specimen, one

could expect to find evidence of several' more. Out of 21 specimens with black

f Iy larvae in their gut, only 8 had one larva. The average was 2.7 black fly

larvae per specimen and the maximum ,was 9. Thus, when Simulium larv'ae are

available.,they are readily preyed upon. Plecoptera were common in the' Wau

area, especially from October ti1l the cessation of water flow (usually in

February). However, their distribution was curious. Despite thé apparent

similarity of Bussere and Wau Causeways, Plecoptera nymphs were much more 1

---,--- 1 -.52- -- ' common a t Bussere Causeway. ft is impossible to quantify the difference due

to the variation in numbers and sizes of samples colIected at both sites,

however, over a period of three' years only one Plecoptera nymph was collected

at Wau Causeway. The most striking difference between the two Causeways is

the surrounding vegetation. The river banks at Bussere are lined with tr~es and

dense vegetation (depending on the season), whereas \Vau Causeway is situated ~ near the town and the banks are almost bare. Due to the high density of

people and the effect of their activltles, few trees remain. This could have

an important impact on the suitabiltty of the habitat to adult· stoneflies and

may be a factor in inhibiting the colonization of Wau .Causeway by Plecoptera

nymphs., , / .. OOONATA. r Odona ta are carnivorous both as immatures and adults (Westfall, 1918), 4- ,~ this makes them extremely interesting as predators of black mes since they c- \" IJ' "" ~ have been repotted as preying on adult Simuliidae (Pritchard, 1964; Laird, 1973)

as weIl as the immature stages.

Zrgonyx. Most of the Odonata were uncommon; members of the genus Zygonyx,

however, formed 4-.696 C?f the predatory population from Apri1-July (period of

increasing discharge) and 396 during the spates (August to November) (Fig. 9).

No specimens were encounte!"ed trom December untiI the cessation of flow.

... Zygonyx, despite it's low density, ~as an important black fly predator. Tt

'!", is the insect' which ate the highest number of black fly larvae (the rn~~n number consumed per individual specimen was 1.67) (Fig. 5), and black flies were by Jr it's preferred prey cornprising .54% of it's diet (Fig. '3al~ - ~ \ -53-

Theoretically it is the most important predator of larval black files and, were it present in sufficient numbers, it would have the potential ta be an important factor in reducing larval black fly populations. J)espite it's low densities, it is the third most important predator of Simuliidae in the Wau area, immedia~ely following the two main Trichoptera.

l've used the expression "feeds preferentially" fr~quentJy in the course of

o this discussion. This expression infers that the animal in question actlvely seeks out certain prey items, aithough this may occasionally be the case, It is likely , that when a predator appears to feed preferentially on a specifie prey Item,

it is simply more accessible in the particular mlcrohabltat in which the J--., \ predator lives. Prey accessibility to a speCifie predator can not be estimated by overall prey densities (whlch mainly indicate the availabdlty of prey to the

entomologist) and is dependent upon numerous factors (which are virtually

impossible to quant if y), such as prey escape tactics and refuges, predator

searching behaviour and stimuli etc. The mean number of Simuliidae consumed

by a specific predator will naturally be the result of aIl these parameters.

Olpogastra.

Olpogastra was rarely collected, consequently only nlne specimens were l ' dissected', 22% of these were positive for black fly larvae, yet Olpogastra has

little potential as an effective black fly control agent due to two factors:

a) the low mean number of black f!les per specimen (O.22) and the' fact

that Simuliidae are the third food choice after Trichoptera and Ephemeroptera;

b) the large number of Cheumatopsyche spp. whlCh It consumes (Fig.

5h). This reduces itls suitabihty as a black fly control agent because it grazes

upon other beneficial inseçts. In tact, if the number of Cheumatopsyche it

consumed i#êreased even slightly, OJpogastra cou Id have a net boosting effect. -54-

on black' ~ly populatIOns due to the removal of, some· of thelr more effiCient

predators. Of aIl the predatory Jnsects assoclated wlth larval S. damnosum,

Olpogastra ranks last In e'ffectlveness as a black fly predator, (Fig. 7).

~~omphus or Crenigomphus. It could not be deterrnlned whether the specles colJected was a member

of the genus Paragomphus or Crenigomphus: It certamly, however, belonged to

one or the other of these genera.

Twenty t~f specimens were dlssected and 9% contamec black fly remains "- in their gut. The mean nUrllQer of black files per specl men was 0.27. It's di et

was ddferent than that of aIl the otner precators Since It IS the on!y speCles

whlch fed equally on all categories of prey (Fig. 3i). Though It consJ'mes

Tnchoptera, It does not feed on me'TIbers of the ge'1us Cheumatopsyche. It's

net effect on the black fly populatlOn IS not very Impresslve Slnce lt doesn't

feed preferentlally on black fly larvae, has a medium voraclty, and occurs in

low densl tes.

CHIRONOMIDAE. v /~ Numbers of Chlronomidae collected ln Wau were low, but a number of

specles were represented (Table 1). Amongst the Chlfonomldae collected, the

only specimens that were potentlal!y predaclOus were members of the genus

Harnlshla (Chlronommae). The deep medium notch ln the mentum o~.these

specimens could be a devlCe for sevenng the head capsu!e tram a prey • 1 (Cranston, 1983 pers. comm.). Only four speCimens of Harnlshla were collected,

t'NO of these were dissected and neither showed any eVldence of predatlOn.

1 -55-

OTHER POTENTIAL PREDA TORS.

There eXlst a few potentlal predators possessing suckmg mouthparts, whose

(~a'rtl1vorous habits would not have been' demonstrated by gut dissections.

Philacollus (Oytiscidae; Coleoptera)

1 Phllacollus IS a dytlscld larva wlth pierclng!suckmg mouthparts, general knowledge about thlS group suggests carmvorous feedmg habits -(Doyen and ~ Ulrich, 1978). One specimen was observed on a stone collected at Wau

Causeway wlth It's mouthparts stuck mto a Chi marra Iarva thus credltmg thls

assumptLOn. No further observatlOns were made on thls beetle, due ta the

turbidity of the water It was virtually Impossible ta make' Oirect observatIOns

in the field and methods such as the preClpltln test or the tmmunodlffusion

test for speCIfie prey would have necessttated more sophlstlCated facllities.

e, VARIATION IN DIET WITH AGE.

The msects examined cou Id be divlded into two groups based on their

voraci ty: the animais wlth hlgh voracity, such as Zygonyx sp., Neoperla spp.,

and Cheumatopsyche sp. VIII (voraclty varymg from 3.06 to 3.86) and those of

medium voraclty (0.87 to 1.54), ~ee Table 3. The voraCity values for these

two groups were slgmflcantly diff~~rèm at the 0.05 leveI. Insects included in

the latter category are: Ch. dlgltata, Ch. coplBsa, Ch. falcifera, and

Amphtpsyche senegalensls. Insects wlthm thlS group show a distinct ,shift in

dlet wlth age. Small specimens fed ~requently on '~trttus" and the larger

speci mens fed more frequently on 'animal matter as mdtcated in Table 4. As

the Size of the anImai mcreased, the percentage of indlvlduals haVmg fed on

prey lf'lcreased, and the percentage 6f mdivlduals wlth detntus orrly in thetr gut ~ 1 decrea5ed. WaIJace (1975) has a150 observed this ln hydropsychld cad4tsflies.

Detritus and prey items often occur together, yet the percentage'

--' r

of animaIs contatnIng detntus only is a c1ëar indicatIOn of the importance of

non animal matter ln the diet. / On the other hand, the hlghly carnlvorous antmals such as (Zygonyx),

showed no Increase ln carntvory in larger specimens. "Jeoperla showed a small

decrease ln carmvory in the lower age groups, but this was not accompanied

by an Jncrease ln the importance ,of detntus, indicating that the increase in

voracity wlth age IS due "to the ablJity ta mgest more prey items, rather than

\ a stuft to a more carnlvorous dlet. For Ch. sp. VIII, the sample size for the

small and medium classes was too 1 small to be able to make any conclusions,

although smaller specimens appeared to be less carnivorous.

lnsects such as Zygonyx and Neoperla should be highly regarded as black

fly predators smce they are carmvorous throughout their growth period.

ln most specles examined, the prey composition did not greatly vary with r age (as Indlca ted by size: (Fig. 8). Zygonyx specimens of ail size classes

fed preferentlally on Simullidae. -

[n the Jess carnivorous species (those with medium voraclty values), the

choice of prey tended to shift towards smaller items such as chironomid larvae

in the small Slze class. The small specimens of Paragomphus or Crenigomphus,

Ch. falclfera and Ch. copiosa never fed on Slmulium larvae, although the

medium and large specimens frequently did (Fig. S). \ Due ta the great variat:ton in the results of gut examinations between

specimens of the same group (be it species or size class within a species), it? 1

lS Important to examme a large number of specimens to obtain reliable results. ~

The analysls of variance performed on \the-~an number of prey items

consumed by each size class shows that for those groups where less than 35

specimens were examined, the confidence Iimits ,on the means were very wide

(Appendix 6), and the results obtained did not depict a c1ear picture. \ '-- \

-...... -...... SEASONALITY OF PREDA TORS.

The following discussion is based on relative abundances only: although the'

results indlcate deflmte trends, they should not be consldered as more than

preHminary insights.

The variation in seasonal relative abundance of the predatory fauna

(Fig. 8) suggested the following points:

a) a negative correlation between the two main black fly predators, Ch.

copiosa and Ch. digitata. When the relative abundance of Ch. copiosa was high

o «(rom 46 ta 51%), during the penod of mcreasing discharge and durmg the

spates, the relative abundance of Ch. dlgitata was low (18 to 26%). The reverse

occurred dunng the period of decreasing dlscharge when Ch. dlgitata was the

dommant element of the predatory fauna (5996) and Ch. coplOsa accounted for '( only 1596.

b) The Tnchoptera as a group appeared to be most Important during\ the

periods of increasing and decreasing discharge, whereas the Plecoptera, which

accounted for only 0.3% and 296, respectively, dunng these penods, increased

ta comprise 1596 of the predatory fauna dunng the spates. Smce these are two 1- major groups of predators, the replacement of one group by another depending

on the season ensures continuous predation upon black fly Iarvae no matter

what the hydraulic conditions.

1lle numbers of Odonata were too Iow ta be able ta suggest any seasonal

trends.

j --58-

IMPORTANCE OF PREDATORS.

These st ud ies constl tu te preliminary observations which conflrm and descrlbe predation of larval black files. \Vith the~e lnslghts' into black fly predation it IS Imperative to quantlfy the effect of larval predation on the population of onchocerClasis vectors. There is very litt le information on the

importance of predators ln regulatmg black fly populations in any area of the

.~ world. The few studles whlCh have been performed ln temperate regions offer

contradictor.y results: Abdelnur (l968) and Ezenwa (I97ft) declared the effects

of preda tors to be neghglble and secondary to those of mermithids. Speir

(1976),10 a quantitative study of blOlogy and population dynamiCs of black fly

larvae in 'Oregon, U.S.A., estimated predator caused lasses to account for 82%

of larval mortall ty.

[t IS always dlfflcult ta quantify biological processes. The evidence of the

~ extent of predation on larval black flIes demonstrated in this study should be

ample encouragement and Justification for a serious effort to be made to

quantify the effects of predation on simuliid populations. There is much

controversy about the importance of predation in the stucture and composition

of aquatic communities (AHan, 1983; Peckars!

basically due ta the lack of information available and the difficulty of creating

experimental situations and contraIs in a stream environment.

[ 'Vü-' -59-

CONCLUSION ..

In the Wau area, invertebrate predators- "J were important members of the faunâ associated with larval black flies. The variety of the associated fauna 'li to some extent related to the irregular, deeply crevic~l substrate., Elouard

(l~83) showed that Hydropsychidae favored stable substrates (rocks) over moving substrates (grasses, trailing branches); and the crevices oHer natur'al refuges . '. which allow the co-existance of high densities of aflimals. In Southern Sudan • the most important predators were Cheumatopsyche digitat?- and Ch. coplOsa

(Hydropsychidae: T richoptera)j these. two species exerted' the grea test Impact on the black fly population. Zygonyx sp. (Odonata), Neoperla sp. (Plecoptera), and Cheumatopsyche sp. ym (Trichoptera) preyed exten~ively on black fly larvae bu t were not present in large numbers: these three specles never totalled more than 18% of the pred~tory p,opulation .. Although the rough ironstone substrate, char acte ris tic of the mam. black fly breedmg, sites ln ·the Wau area harboured numerous predators, the large numbers of adult black flles and high transmissiOn rate of onchocerclasis in the area show tha t the predatory fauna is far from exerting an acceptable levei 'of control.

Nevertheless J predators are important elements 1 ln the lIfé cycle of larval black files and could be of relevance within the context of a multi-faceted approacft to reducing onchocerciasis.

The r igidity of the present insecticide ba'sed <:ontr~l programme causes difficulties which do not ,make it suitable as:a long term solutiOn to.' onchocerciasis. More flexible multi-faceted strategies will have to be incorporated into existing .control programmes 50 as to ensure their long term t;t efficacy.

À multi-~a.ceted approach to onchocerclasis control \l.(oul<;l include ..... -tiO-

strategies such as habitat management (causeway removaT, regular weeding of

localized· beds etc.), village location (especially in areas being recolonized), use

of alternative hosts (cattle,. goats etc.), use of repellents (sesame seed oil is • used in Northern Sudan) (Ahmed, 1976), socio-economic changes (patterns of

agricul~re, population density), availability of water 10 the' village to decrease

time spent by- the river and timing of stream related activities (fishing,

"washing), and the creation of a "black fly barrier" by eliminating a ~ forest gallery between the village and the river. These are just a few examples

of some of the possible components of a multi-faceted approach to , . onchocerciasis control. The methods employed will vary with region and time.

and many original schemes will evolve.

For most of these methods to be sustamable over a long period of hme

it is imperative that they be applied by the local population ln endemic area5, .. 1 and ideally they should be planned and inltiated by the concerned population. Since such alternative strategies are rarely observed, It i5 .important ta deteroùne which are the driving and restaming forces affecting the populatIon.

Such a study would enable one to strengthen the eXlst·mg dnving forces and

weaken the restrainmg forces sa as to fac1l1tate the implementation 'of locally

applied control measures•

..

1 -61-

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SERIVICE, M. W. 1973 b. Mortaltties of the larvae of the Anopheles gambiae complex, and detectlon of the predators by the precqJlttn test. Bull. Ek;,t6moI. Res. 62:359-369. SER VICE, ~\ 1973 c. A study of the natural predators of :'\edes cantans (Melger) USlng the preclpitln test. J. Med. Entomol. [0(5):503-510 J CE, M.W. and J.-M. ELOUARD. 1980. SerologlCal Ident!flcatlOn of the predators of the complex of Slmul1um damnosum (Dlptera: Simullldae) 10 the Ivory Coast. Bull. Entomol. Res. 70(4):657-663.

, M.W. and P.T.W. LYLE. 1975. Detection of the predators of Simullum damnosum by the preClplttn test. Ann. Trop. Med. ParasitaI. 69:105-108.

SHELDON, A.L. and M. W. OSWOOD. 1977. Blackfly (DLptera: Simuilldae) abundance ln a lake outlet: test of a prediCtive mode!. HydroblOlogla 56:113-120 l"'\

SHELLEY, A.J. 1983. The identitles of the Brazillan blackfltes (Dtptera: Simuludae) reported ·by Lutz and Splendore as hosts of microspondia. J. Inv. Pathol. 42:280-281.

SIMMONS, K. 1983. Personal communication. Dept. of Entomology, University of Massachussetts, Amherst, U.S.A. , SOMMERMAN, K.M. 1962. Notes on two species of Oreo eton predaciOus on black fly larvae. Proc. Entomol. Soc. Wash. 642 :123-129.

SPEIR, J.A. I97c6. The ecology and production dynamics of four black fly species (Diptera: Simuludae) in Western Oregon streams. Ph.D. thesis, Oregon"State University.

STATZNER, B. 1981. A progress report on Hydropsychidae from the Ivory Coast: Characters for the specifie identification of larvae and \ ~ population- dynamics of four abundant species. Proc. of the 3rd Int. Symp. on Trichoptera. G.P. Moretti (ed.). Series Entomologica Vol. 20. Dr. W. Junk Publ. The Hague.

ST A TZNER, B. 1982. Population dynamics of Hydropsychidae in the N'Zi Ri ver (Ivory Coast), a temporary stream partly treated with the insecticide chlorphoxim. Rev. Hydrobiol. Trop. 15(2):157-176. -68-

STA.TZ'\JER, B. 193:'. Keys to adult and Im'Tlature H~'dropsyc:f"l1dae ln the Ivory Coast ('J, es: .'\fnca) \\'1:'-1 notes on the!r taxonomy and distrIbutIOn. Splxlana 7(! ):23-50.

STATZ~ER, B. and F."1. GIBC''>;, 19810, Key ta adults and Immature \~acronematll'1ae (Insecta-Tnchop:era) from the Ivory Coast (West v .A.. frlca) wlt" notes or thelr taxonomy and dlstnbutiOn. Rev. 1 HydroblOl. Trop. (m press). STEEL, R.G. and J.H. TORRIE. 1980. Pr:nclples and Procedures of Statl5tlcS.

A BlOmetrIcal A.pproach. Second ed. \kGraw Hill, \1. Y 0

STEWART. K.W., G.P. FRIDAY and R.E. RHA'vIE. 1973. Food habits of hellgrammtte Jarvae, Corydalus cornu tus (~egaloptera: Corydalldae), ln the Brazos River, Texas. Ann. Entomol. Soc. A.mer. 66:959-963

SWEENEY, A.W. and D.W. ROBERTS. 1983. Laboratory evaJuatlon of the fungus Culicmomycès c1avosporus for control of black fly (Dlptera: Simullldae) larvae. EnVIron. Entomo!. 12:774-778.

TAKAOKA, H. 1980. Pathogens of black fly larvae 10 Guatemala and thelr mf luence on natural populatlOns of three speCles of onchocerClasls vectors. Amer. J. Trop. ~ed. Hyg. 29(3):467-472.

TINS LEY, T.W, 1979. The potentlal of Insect pathogenlc Vlruses as pestlcldal agents. Ann. Rey. Entomo!. 24:63-87. "

TsA CAS, L. and .R.H.L. DISNEY. 1974. Two new AfrlCan speCles of Drosophda \{Dlptera: Drosophdldae) whose laryae feed on Simulium (Dlptera: Slmull1dae) larvae. Tropenmed. Parasitoi. 25:360-377.

TSOMIDES, L 1984. Personal communication. Dept. of Entomology, UnIversity of Marne, Orono, U.S.A.

TWINN, C.R. 1939. NJtes on sorne parasites and predators of blackflles )

UN DEEN 1 A.H. and R.A. NOLAN. 1977. Oyarian mfection ancl fungal spore oVlposition in the blackfly Slmulium mlxtum. J. Inv. Pathol. 30:97-98.

VAJIME, C.G. and R.W. DUNBAR. 1975. ,Chromosomal identificatiOn of the subgenus Edwarsellum near and induding simulium (Edwardsellum) damnosum Theobald (Diptera: Simullldae). Tropenmed. Parasitol. 26:111-138.

VARVA, J. and A.H. UNDEEN. 1981. Microspondia (Microspora:Microsporidia) from Newfoundland blackflies (Diptera: Simulildae). Cano J. Zool. 59:1431-1446. J WADSWORTH, G.R. 1977. A new approach to the problem of river bhndrtess. In: Onthocerciasis in Zaïre. Pergamon Press. Oxford

• -69-

WALLACE. J.B. 1975. The larval retreat and food of Arctopsyche; with phylogenetlc notes on feedmg adaptations m Hydropsychldae Jarvae.' A.nn. Entomol. ')0,. A.mer. 68:167-173.

W.A.LSH, J.F., J.B. DAVIES, B. CLIFF. 1981. Tite World nealtlt Orgamzatlon OnchocerClasls Control Programme ln the Volta River BaSin. ln: Blackfl!es: The future for blOlogJCal methods ln mte rated control.M. Laird ed .. AcademlC Press. London.

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WIGGINS, G.B. 1977. Larvae of the North Amertcan caddlsfly genera (Tnchoptera). Umv. of Toronto Press. Toronto.

WILLlA\1S !\J.E. and H.B. '\J. HY~ES. 1973. ~,hcrodlstrlbutlOn and feedmg of the net-splnning caddlsflIes (Tnchoptera) of a Canadlan stream. Olkos, 24:73-84.

WINTERBOùRNE, ~.J. 1971. The hie histones and trophlC relatlOnships of the Tr Ichoptera of 'v'Ianon Lake, Brltlsh Columbia. Cano J. Zool. 49(5):623-635.

WORLD HEAL TH ORGANIZATION. 1983. Report of the steering committee of the SClentlflc Workmg Group on fdariasls. Jan 1980-June 1,983. TOR/FIL/SC-5WG (80-83)/83.3 wu, Y.F. 1931. A contribution to the blOlogy of SlmuJium (Diptera). Pap. Mich. Acad. SC!. 13:543-599

Z WICK, H. 1978. Slmuludae. In: Llmnofauna europaea. Eine Z usammenstellung' aller -che europaïschen Bmengewâsser bewhonenden mehrzelllgen Tierarten mit Angaben über Ihre Verbreltungund 6kologle. pp:396-403 (2nd ed.) J. Ilhes (ed.) Stuttgart &: N.-York. G. Fischer Verlag; Amsterdam. 5wets &. Zeitlinger B.V.

t ~. SUDAN .tr.,/1 tw_ --\ ;'

KORDOFAN T ( ~ DARFUR , J ,'- 1 (""-.J. l , '-.'- ___ .... (\ (",.... ",' l . ,. __ J " l' :{ ,,' \ !

CENTRAL

AFRICAN

RE PUBLIC

-...1 « " C) '~\\(~~--- ZAIRE ,,/\

-",- --" '" \~L' - ~ KENYA Figure 1. Map of Southern Sudan. , '. \ , .'

-71-

~ ...... ,~ .. , ,, , ,, ,, ""'-

\ " \ ~"-\ \ ., \ \

, " " , ~f, 1 1 1 ,, 1 ,, , ,, ) ,, ,, l' 1 1 1

, Human hab; tation Road ~ River * Main sampl ing site Figure 2. Map of ~ampling sites near Wau (Bahr-el-Ghazal Province) .

._~~ .. -.,------_._------72-

•

Il 21 ..

.~

23.5... •Zygonyx sp. Cheumalopayehe dtgItata ChMlmatop.yehe ~ ------

1~

Neoperla .p. Olpog.. tra .p.

3 ..

20.5" 20.'''' 28..5,.

20.a" PeravomPhua Of Cntnlgomphua

"" ~,. -, '\ .... ,,",\ Simuilum Trichoptora Ephomeroptera Chlronomldao Ott.. ,.

Key to Prey

Figure 3. Percentage of different prey items per predator. ------,-~ ------.. ", ,

-73-.

-,:-- ....

21 ...

17'lo 12"'lo SlmuHum available SimuUum unavailablè Cheumatopsyche digitatà

14,5'"

~2.5'"

24...

26% 23.5'lo Q SlrnuJium available Simullum unavailable

" , Cheumatopsyche copiosa

. "

Key to Prey

Simulium Trlchoptera Ephemeroptera Chironomldae Others

Figure 4. Comparison of the percentage ,of different prey items found in the guts of two Hydropsychidae collected in the presence and absence of Simulium larvae. ',.

1.17 1.11

_ ...~,u,g2

Zygonyx ap. Neoperla sp. C~umatopayche Sp. VI"

O.$4t

Key to Prey

Simuilum

Che.-top.yche' dlgAla.. Paragomphu. or Cremgomphua oTrichopto",

Ephèmeroptera

++ - 0.4<4 Chlronomidae g+++

Othera o O.o~-i"

Olpogaetra sp. Amp~IPeYChe aenegalensls

Figure 5, Mean number of prey items per predator.

" -75-

~--- ... ~ ! ~ 1." , -èà 1 ".. i... ~ 'Ill •... ~ ~ ~ 8 ... a 1 1 ~ ~ ; ~ • 1 ~ 1 et 1 1 .. :1:) • ~ !.. i 1 ;" :, ! • ,'II1II i 1 ~ 1..

Fl gure 6. Comparative importance of nlne predators ln j controlllng larval black fly populat;~ns, \, assumlFlg all predators are present ln eaual numbers.

2.0 /

"' i .. ~ - '" ... ~, - 1 1.. ~ t ! • S 1 , 1 0 .. t == .. , 1 ~ ~ ; ..\! 1... 1 1 ~ ! 1 v 1 ~ 1 .. \' ~

Figure 7. Comparati ve importance of nine predators in cOlltrolling larval black fly populations, taking into account their annual relative abundances. \ \ 2.1. , ..

" ...... , u --' .~ ... "." _! ',:~'-: 128 o ~:'~I_- il ID ~ 1 Il Key 10 Prey

072 '.31

1.11

L M s Neoperls Sp. 011

a 0.10 L .. s Zygonyx sp. - o 0 0.17 L 5 Paragomphus or Crenlgomphua

0.2' 0.11 0.21 O.U 044 0.01 .07 • , " It-t'E.... -~~ .~D~ L .. s 001 001001 Cheumatopsyche dlgltatll o r::J 0 t.,., - L u- s Cheum8topsyche fa/citera 0.38

J 0.01 0.010 01 0.010 01 040 041 ci 42 o " .Hm 0 0 0 0 HiC':l 1 L Il s --J Cheun18topsyche cap/osa (TI 00 Figure 8. Varlatlon of diet composl~10n dependlnq on the L Il s / Amphlpsyche seneg8/ens/s size of the predator. ~lean numbers .of prey per predator

~: large, M: me

AMPHIPSYCHE SENEGALE'NSIS r:1 OLPOGASTRA ~ PARAGOMPN(JS OR CRENI60MPHUS Il NEOPERLA

ZYGONYX

[~(J CHEUMATOPSYCHE SP. ...

00 0 0 0 0 :0 0. CHEIAIIATOP$YCHE F'ALCIFERA 0 0 0 ft C

o CHEl/MATOPSYCHE COP/OSA

CHEtNATOP$~E D/fl/TATA

PI" P2 P3

Pl: Apnl-July -, PZ: August-March "­ J P3: Oecember-March The numbers above the columns indicate the number Of specimens .. collected for each season . Figure 9. Variation in seasonal relative abundance of the predatory fauna. " -78- Table 1. LIST OF AQUATIC INSFCTS rFO/l LOTIe HJ'EITATS OF THE v'AU AFEJ\, SOUTHERN SUDAN.

TRICHOPTERA Hydropsychidae (Macronematinae) 4 Amphipsyche senegalens i9 (Brauer) 2 Aethaloptera dispar Brauer (Hydropsychinae) 4 Cheumatop$Yche copiosa Klllmlins 4 Cheumatopsyche falcifera (Ulmer) 4 Cheumatopsyche digltata (Mosely) 2 Cheumatopsyche sp. VIII Phi lopotamidae 4 Chimarra sp. Hydropt i l idae l genus indet. Leptoceridae l Oecetis ghibensis Kimmins * Oecetis maculipennis Ulmet, * Ceraclea shoucedeni Navas Dispen

EPHEKKROPTE.RA Tricoryth idae 4 Tricorythus sp. 01 igoneuridae 4 Elassoneuria sp. Heptageni idae l Afronurus sp. Baetidae 2 Centroptilum sp. 2 genus indet. Caenidae 2 genus indet. Leptophlebi idae * genus indet. Polymitarycidae ** povilla adusta

ODOHATA Gomphidae 2 Paragomphus or Crenigomphus l Ietinogomphus or Gomph idia Libellul idae 2 Zygonyx s p. 1 Olpogastra sp. \ * Tholymis tqlagra (Fabr.) * Pantala flavescens (Fabr.) * lacustris Kirby * Brachythemis leueostica (Burmeist.) * Trithemis bredoi Fraser * Trithemis aconita Leiftinck * Olpogastra lugubris Karsch * Tramea basilaris (Beauvais) Cordulidae * Macromia sp. * Maeromia 'sp. (pieta group) Coenagrionidae * Ceriagrion sp.

PLECOPTERA Perlidae Neoperla needhami Les tage 3 Neoperla sp.

.. -79-

(Table 1 continued)

COLEOPTERA Elmidae 4 Potamodytes sp. (adults) 2 Potamodytes sp. (larvae) 3 other Elmidae (Sb, Sc, Se, SE) Hydrophilidae 1 Hydrocus sp. I genus indet. Dytiscidae 3 Philaccolus sp. Gyrinidae ** genus inde t • HEMIPTERA Gerridae ** Limnogonus (leptocerus?) Pleidae ** Plea puilula o Corixidae ** Micronecta sp. ** Sigara hedenborgi Naucoridae ** Macrocoris flavicollis Nepidae ** Ranafra pavuipes (vicina)

DIPTEIlA Chironomidae + Skusella pallidipes (Kieffer) (Chironomiq.ae) 3 Polypedilum (sp.A, sp.B, sp.c) + Stenochironomus sp. + Stictochironomus fusiformis Kieffer 1 Harnishia sp • . (Tanypodinae) + Pentateurini (genus indet.) (Orthoclad i inae) + Cricotopus sp. * Cricotopus sudanicus Freeman

Tipulidae 1 Antocha sp.

Ceratopogonidae l Ceratoponinae genus indet.

Simuliidae 4 Simulium damnosum s .1. ? Simu1ium damnosum s. s tr. 4 Simulium d. sirbanum 4 simulium griseicolle 4 Simulium adersi 4 Simulium hifila 2 Simulium cervicornutum 2 Simulium schoutedeni 'i Simulium bovis 1 Simulium alcocki 1 Simulium hargreavesi 1 Simulium unicornut!tjm

* : sl'é~imens co11ected as adults only, from 1ight traps at Bussere Caus~way, -lar'La) habi tat unknown. ** : -rare specimen, probably coI1ected from slower running waters - + specimen present, numbers not counted 1 rare (0-10 specimens collected over the three year period) 2 occasional (Il-50 specimens collected over the three year period) 3 common (51-100 specimens collected over the three year period) 4 abundant (more th,.an 100 spec imens co 1lected over three years).

__.0.-

--._--~ f -80- "--

"

... "

Table 2. IŒSULTS 01' TRI GOT .AlW.YSIS OF. 19 SPECIBS OF tRsICTS COI.I.ECTED III ASSOCIATIOII vr'lB LAJNAL Bl..A(% PLIIS. PDCDTA.GIS OF SPECIMI1IS POSITIVE l'OR SIMULIlDI LARVAE.

I1ISECT DISSECTED % POSITIVE Il POil Smul i ....

TRICHOPTERA + Amphipsyche senegalensis 2.8% (107) Aethaloptera dispar ' 0.0% (11) -+ Cheumatopslche digitata 36.0% (204) .. + Cheumatopslche copiosa 21~7% (87) + Cheumatopslche falcifera 22.2% (93 ) + CheumatopsI'Che sp. VIII 42.8% (21) Chimarra 0.0% (38) Oecetis ghibensis 0.0% (4) Hydroptilidae 0.0% (I)

EPHEMEROPTERA Tricorlthus 0.0% (138) Elas8oneud.a 0.0% (16)

ODONATA + Zlgonlx 54.5% (,34) \ . + Olposastra 22.2% (9) + Paragomphus or Crenisomphus 9.0% (22) + Ictinosomphus or Gomphidia 100.0%' (1) Q

PLECOPTERA \ + Neol;!erla 29.0% (72)

COLEOPTERA S +/- Philaccolus 0.0% (18) Potamod~tes {adults) 0.0% (4) ,,- Hydroph11 idae 0.0% (6) + : Predators or predac~' us omnivores : Exclusive vegetarian and/or detritu8 feeders S +/- : Insects with Su king mouthparts for which there was 8011le evidence of predation based on field observations.

\ ,

...... _-..• .,...... -----~------_._---~--_... ."."-,------81- "

" Table 3. VOlU\CITY VALUES FOR EACH SPECIES OF PREDATOR ASSOCII\TED WITH LARVAL BLACK FLIES IN SOt1l'BERN SUDAN. "

SRens VORACITY X hET X DETRITOS X lKP1"1'

ORLY GOT

Cheuma t028Iche digitata 1.51, 74 18 8

Cbeuma t025.lche falcifera 0.87 60.5 2105 18

Cbeumato2sIche copiosa 0.86 56 35 9

Cbeumato2sIche sp. VIl! 3.86 86 4.5 9.5 0 Amphipsyche senegalensis 1.04 39 52 9 • Neoper la spp. ].49 83.5 0 16.5

Zygonyx sp. 3.06 76.5 0 23.5

--.. j ...~ ~ 01l!0sastra sp. 1.11 33.5 11 55.5

Parasomphus or CreniS01ll}!hus 1.54 91 0 9

~ Voracity : Hean number of prey items per individua1; X Prey : % specimens containing animal remains; % Detritus on1y : % specimens containing detritu8 only; % Empt}' gut : % specimens vith empty' guts.

1

q

------...... ,------_..... ,_.- ... -...------~ -82- '.

•.,

" Table 4. VOUCIt"l VALOIS PD SIZE euss OP UCH snCIES" OF PREDA'l'OR. ASSOCUTED - VITH IAllVAL ILlCl: nus._ ('. \ SPECB!? SIZE VORACITY % PuY % DETIlITUS % EKP'l'Y ORLY GOT

Cheumatopsyche digitata • L 1.89 87 10 3 M 0.75 65 25 10 S 0.69 40 40 20

Cheumatopsyche falcifera L 0.97 79 15 6 M 1.15 68 27 5 S 0.15 15 20 65 ... Cheumatopsyche copios4 L ' 1.08 63.5 31.5 5 1 ~ M 0.25 40.5 37.5 22 S 0.18 25 56' 19

Cheumatopsyche sp. VIII ,L 4.69 94 o 6 M 0.5 50 50 o S 1.67 67 o 33

Amphipsyche senegalensis 1.23 48 47 5 1.25 42.5 .. 50 7.5 0.40 14 68 18

Neoperla spp. L 3.68 78 o 22 M 3.74 93 o 7 S 2.57 71.5 o 28.5

Zygonyx sp. XL 2.50 67 o 33 L 4.86 71.5 o 28.5 M 2.88 87.5 o 12.5 S 2.44 75 o 25 .... ParagomphU's or Crenigomphus L 1.29 o o LOO S, 2 87.5 o 12.5

Voracrty : Mean number of prey items per individ~l in a given size class; ~ % Prey : % specimens containing animal remains in a given size class; % Detritus only : % speëimens containing detritus on1y in a give'n size class; % Empty gut : % specimens with empty guts in a given size c1ass

t __ L -83- APPIIID~ 1. Line dravinae of the .,.t iaportaDt chitilloue part. u.ed· for det"taillilll' prey origill.

:

Anal sclerite Simul iidae 2 serrations (a11 Simul'ium except i. gris~icolle) b. v 1 serration: Simulium gr;seicolle r/ --V- \ a. General Simùlium mandible \ ) b. Detail of serrations

arc form

Hypostomial teeth Hypos tomi. a 1 teeth Simulium adersi Simulium'damnosum·

Hypostomial teeth Cephalfc fan (partial) Sfmulium griseicol1e Sfmul il dae

Il

SClERITES FROM SIMULIIDAE

, . -APPEllDIX 1. (cont 'd)

Mandibles Mandible

Cheumatopsyche sp. Aethaloptera dispar

"

Mandi b 1 e Chimarra sp,. Tri choptera Tarsal cl aw Mandible Amphipsyche senega1ensis

Anal prolegs Hydropsychidae Anal prolegs Oecetis sp.

SCLERITES FROM TRICHOPTERA , \

_,______-~ ___ f APPENOIX 1. (cont'd) -85-

Mandible: Tricor~thus Mandible: Elassoneuria

'" Tarsal claw: Tricorythus Tarsal claw: Elassoneuria

/

/

Tarsal c1aw: other Ephemerpptera• e,

SCLERITES FROM EPHEMEROPTERA

_:'..---______1t "

APPENDIX 1. (cont'd) -e6- o'

\

Hypostomial teeth Hypostomial teeth Polypedilum sp. C Cricotopus sp.

, .. ~.:'; .~::'· , . ' .r- ~ -_ ... _~ M ~~~... j) Hypost~ial teèth Hypostomial teeth Harnishia sp. Stenoch1ronomus sp. , .

Chironom1dae ( Claws of posterior parapod

SC~ERITES FROM CHIRONOMIDÂE

__- ___ J l', APPENDIX 1. (cont'd) " -87-

Tarsal claw: Oyti scidae Mandible: Dytiscfdae

\

Tarsal claw: Elmidae

Egg: Elmi dae

SCLERITES FROM COlEOPTERA \

(0 -88- APPDDIX 2 .. Te.tios tbe bypothe.is tbat aIl prey categories oeeur. vith equal frequeucJ.

> '- SPBCl;BS PROBABILITY OP A GREATBR VALUE

.Qh.. digi tata 41.54 p < 0.005 Ch. eopio84 16.52 p c;;.Q." 005

Ch. > falcifera > 19.82 P ..lE' 0.005 Ch. 8p. VIn 31.89 p < 0.005 Amphi. senegalensis 43.02 p < 0.005 Neoperla sp. 126.94 p < 0.005 Zygonyx sp. 81.42 p <0.005 !!!!!.. or Crenigomphua 0.41 0.975 < p <: 0.990 Olpogastra sp. 5.00 0.250 < p <: 0.5'00

~ The l-evel of signifieanee was set at the 0.05 leveI.

1

_ / >(i

\

'- '" 1 ---~_.. - - >. . .-_.------.--fi ,. • .. ~ -.>~------_...... ------~-- , " } -89- APPERDU 3.

Analyaia of variance on ~an nUllbers' of prey items conau.ed by nine predators in tbe presence of Sia.lliua larv.ae.

o SPECIES OF PRJmATOR. R PREY ITEMS, MEAN C.L. VARIANCE - (+/-)

Simulium 0.54 0.13 0.81 Trichoptera 0.25 0.08 0.20 Cheumatopsyche disitata 158 Ephemeroptera 0.23 0.06 0.19 Chj.ronomidae 0.31 0.10 0.39 Other 0.18 0.12 0.20 Total 1.51 0.23 2.14

Simulium 0.26 0.10 0.27 Trichoptera 0.07 0.06 0.08 Il Cheumatopsyche copiosa 129 Ephemeroptera 0.20 0.08 0.22 Chironomidae 0.21 0.08 0.24 Other 0.12 0.06 '0.13 Total 0.86 0.20 1. 21 ,- Simul ium 0.23 0.10 0.20 Trichoptera 0.03 0.04 0.03 0 \Cheumatopsyche falcifera 90 Ephemeroptera 0.22 0.12 0.38 Chironomidae 0.27 0.12 0.38 Other 0.11 0.08 0.12 Total 0:87 0.26 1.47

Simu1 ium 0.62 0.44 0.95 1 Trichoptera 0.05 0.10 0.05 Cheumatopsyche, 8p. VIn 21 Ephemeroptera 1.48 1.15 6.49 Chironomidae 1.10 ' 0.71 2.49 Other 0.62 0.33 0.55 Total 3.86 1.90 17.23

Simulium 0.03 0.04 0.03' Trichopte'ra 0.10 0.06 0.09 Amphipsyche senesalensis 104 Ephemeroptera 0.21 0.08 0.2~ Chironomidae 0.37 0.16 0.64 Other 0.34' 0.14 0.5~ TotaL 1.04 0.'34 2.85

Simulium 0.91 0.46 3.51 Trichoptera 0.43 0.14 0.34 Neoperla sp. 67 Ephemeroptera 0.22 0.12 0.21 Chironomidae 1.61 0.78 8.54 Other 0.31 0.12 0.28 Total 3.49 1.04 18.07

Simulium 1.67 1.06 8.85 Trichopt;,era 0.24 0.24 0.50 ~Zygonyx sp. 33 Ephemeroptera 0.48 0.26, 0.57 Chironomidae 0.55 0.31" 0.76 t Dther 0.12 0.12 0.11 Total 3.06 1.39 15.37

(continued next page)

-----~--'.. __ ...- -90- (Appendix 3 continued)

-r

SPECnS OF PREDA'l'OK R PREY ITEMS MEAIl C.L. VARIANCE (+1-)

. Simulium 0.27 0.48 1.16 Parssomphus Trichoptera 0.32 0.21 0.23 or 22 Ephemerôptera 0.32 0.21 0.23 Crenigomphus Chironomidae 0.36 0.35 0.62 Other 0.27 0.25 0.30 Total 1 ;'55 0.69 2.45

Simulium 0.22 0.35 0.19 Trichoptera 0.44 0.'55 0.53 Oleosastra sp. 9 Ephemeroptera 0.33 0.55 0.50 Chironomidae 0.11. 0.25 0.11 Other 0.00 o 00 O.QO Total 1.11 1. 61 r..36

\

( 1 , l,/1 / -91-

APPIDIDIX 4.

Tukey' s v-procedure: Te.t.ing signifieant difference. a.ongst _an voracitiee of nine apeciea of predators. ' sp. bV!II Neop. Zygon. Para. C.fal. --C.cop. 3.86 3.49 3.06 1.54 1.51 l.l1 - 1.04 0.87 0.86

The critical level was set at 0.05 and the crieical, value was 2.04.

1

------_._---- -92-

APPENDIX 5 ~ .

Head measurements used to determine size c,lass. }<1hen head measurements overlaf'ped' body length was taken into account.

SPECIES SMALL MEDIUM LARGE

cheumatoeSIChe~i&itata 0.45 - 0.60 0.70 - 0.75 1.00 - 1.15 CheumatoesIche a1cifera 0.40 - 0.55 0.50 - 0.70 0.70 - 0.95 Cheumatoes:lche coeiosa 0.40 - 0.60 0.55 - 0.70 0.70 - 0.90 CheumatoesIche SPI VIII 0.'66 0.80 - 1.00 Amphipsyche sene'galensis 0.40 - 0.70 0;70 - 1.00 0.90 - 1.10 Neoperla SPI 0.80 - 1.40 0.90 - -2 20 2.30 3.50 ZIs~nlx sp. 0.70 - 1.30 1.50 - 2.00 2.30 - 2.70

.',

• •f, •1 . •1 • 1 Ï4 1 ..;

\. a. Cheumatopsyche (dors1l/ b. ~pmhipsyche (dorsal); c. ~operla (dorsal) -

d. Zygonyx (dorsal).

\'

" ~ , -94-

(Appendix 4 continued) ù SPECUS OP PIIIDl'lOR. SIZE PREY ITEM HIWI C.L. VAIlIAlfCB • "(+1-)

Simulium 0.00 0.00 0.00 Trichoptera 0.00 0.00 0.00 Che~topsyche c02iosa S 11 Ephemeroptera 0.00 0.00 0.00 Chironomidae 0.09 0.20 0.09 Other..". 0.09 0.20 0.09 Total 0.18 0.40 0.36

Simulium 0.26 0.16 0.20 Trichoptera 0.03 ' 0.06 0.03 Cheumato2slche falcifera L 31 Ephemeroptera 0.32 Ô.18 0.23 1 Chironomidae 0.19 00'14 0.16 Other 0.16 0.16 O.~l Total 0.97 ' 0.37 O. 7

Simulium 0.33 0.16 0'.28 Trichoptera 0.03 0.06 0.03 Cheumatol2slche fa"leifera M 39 Ep.hemeroptera 0.26 0.26'_ 0.67 0.44 -' Chironomidae 0.26 0.67 Other 0.10 0.10 0.09 Total 1.15 0.4i 2.24 \ Simulium 0.00 0 0.00 0.00 ~ Trichoptera 0.05 0.10 0.05 Cheumato2slche faleifera S 20 Ephemeropt-era 0.00 0.00 0.00 Chiron01llidae 0.05 0.10 0.05 ~ Other 0.05 0.10 0.05 Total 0.15 0.17 0.13 \ Simulium 0.03' 0.06 0.03 Trichoptera 0.10 0.10 0.09 AmphiesIche senej5alensis L 39 Ephemeroptera 0.28 0.16 0.26 Chironomidae 0.46 0.28 0.73 Otber 0.36 0.24 0.55 Total 1.23 0~55 2.92

Simulium 0.02 0.04 0.02 Tt'Ïchoptera 0.10 0.10 0.09 M t AmphiesIcbe senesalensis 40 Ephemeroptera 0.22 0.16 0.23 Chironomidae 0.47 0.31 0.87 Other 0.42 0.29 0.81 Total 1.25 0.63 3.83

Simulium 0.04 0.08 0.04 Trichoptera o.oa 0.12 o.-oa AmehiesIche senesalensis S 25 Ephemeroptera 0.08 0.12 0.08 ehironomidae 0.04 0.08 0.04 >:> Otber 0.16 0.19 0.22 Total 0.40 0.37 0.83 ','

(cont~nued next page)

'------~ " ., , -' -95-

(Appendix 4 continued) , SPECIES OF PDDA.roa. SIZI PUY n'III lIIAJr C.L. V~ '" • (+/_) f

Simulium 0.72 0.58 2.13 Trichoptera 0.52 0.25 0.34 Neoperla sp. L 25 Ephemeroptera 0.16 0.14 0.14 Cbironomidae 1.96 1.53 13.62 Other 0.32 0.23 0.31 Total 3.68 1.82 19.48

simulium L11 0.90 5.26 Trichoptera 0.44 0.25 0.41 fs' Repperla sp. M 27 Ephemeroptera 0.26 0.19 0.20 Cbironomidae 1.52' 1.09 7.72 Other 0.41 0.23 0.33 Total " 3.74 1.87 22.51

Simulium . 0.57 0.78 1.80 Trichoptera 0.29 0.28 0.22 Neoperla sp." S 14 Ephemeroptera 0.29 0.35 0.37 Cbironomidae 1.29 0.86 2.22 Other 0.14 0.22 0.13 Total 2.57 1.17 9.49 .. Simulium 2.86 4.99 29.14 Trichoptera 0.57 0.91 0.95 Zygonyx sp. L 7 Ephemeroptera 0.71 0.88 0.90 Cbironomidae 0.57 0.73 0.62 Other 0.14 0.34 0.14 • Total 4.86 6.56 50.14 Simulium 1.13 1. 37 2.70 Trichoptera 0.38 0.86 1.13 Zy,onyx sp. -"" M 8 Ephemeroptera 0.50 0.78 0.86 Cbironomidae 0.50 0.45 ' 0.29 Other 0.38 0~43 0.27 Total 2.88 2.55 9.27

Simulium 1.38 1.13 4.52 Trichoptera Q.06 0.13 0.06 Zygonyx sp. S 16 Ephemeroptera 0.38 0.32 0.38 Chironomidae 0.63 0.58 1.18 -#I..:;r- Other 0.00 0.00 0.00 Total 2.44 1.26 5.60

simulium 0.43 0.78 1.80 Paragomphu9 Trichopterà 0.50 0.30 0.27 or L 14 Ephemeroptera 0.14 0.22 0.13 Crenigomphus Chironomidae 0.07 0.15 0.07 Other 0.14 0.22 0.13 Total 1.29 0.91 2.53

Simulium 0.00 0.00 0.00 Paragom!>hus S 8 Trichqptera 0.00 0.00 0.00 or E~eroPtera 0.63 0.43 0.27 Crenigomphus Chir nomidae 0.?8 0.95 1. 27 Other 0.50 0.64 0.57 Total '2.00 1.25 2.29

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~~PENDIX 7. Patterns of proventricular teeth. Proventricular teeth of ~~~tfr~y;he , copiosa 'Kil\'\I"lins, Trichoptera: Ilydropsychidae. (Objective Xl00). \0 C'I,

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APPENDIX 7. Proventricular teeth of Cheurnatopsxc~ digitata (Mosely). (cont'd) Trichoptera: HYdropsychidae. (Orjective,X100). , ''-0 -..1 1

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1 APPENDIX 7. Froventr~cular teetr. of .l.J"1phl.rsyche seneaalensl.S (Brauer). (cont'd) Trlchoptera: Eydrop,sychidae. ) Cl jecti 'le XIOO} , o ~ ~,

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~ Proventricular tee th of rheu~Rtnpsvche sp. VIf 1 flPPEtlDIX 7. ~ Trichopter~: Hydrnrsychidae. (nb~ective X400), (cont'd) f? ~.\, , ,

o o 1 :'

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Cl -:.

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1 - -102-

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JlPPHIDIX 7. Proventricular teeth ~f 7~nonyx sp, (Objective Xl00). (cont'd) Odonata: Libel1ulidae ".

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