Entomological report on development of the Shire River Valley
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00103289/00002
 Material Information
Title: Entomological report on development of the Shire River Valley
Physical Description: Archival
Language: English
Creator: Berner, Lewis ( Author, Primary )
Carr, Archie Fairly 1909- ( Author, Secondary )
 Record Information
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UF00103289:00002

Full Text

Entomological Report


Development of the

Shire River Valley.


Lewis Berner, B.Sc., M.Sc., Ph.D.

Archie F. Carr, B.Sc., n.Sc., Ph.D.

Ist February, 1953

University of Florida





Introduction . ........... . . . . . .. 1

Objectives . . . . . . . . . . . . . . . . . . . a . . 2

Itinerary . . . . .. . . . .. . .... . . . .. . .3

Physiography . . . .. . . . ........ .. . . . . . . ..

Geology .. * . a , . . * . . . . . . . . . . . . 7

Climate . . . . . . . . . . . . . . . . . . . . . .

The Lake . . . . . ... .. . . . . . . . ........... 11

The River .. . ..... . . .... . . . ...... . . .. 13

Population . . . . . . . . . . . . . . . . . . . . ....... 17

Malaria . a . a ........a ...... . . .. . 1

Malaria Vectors . . . . . . . . . . . . . . . . . a a . . . . 21

General discussion and recommendations .. . . . . . . 35

Filariasis . . . . . ... . . . . . . . . . . . 49

Onchocerciasis 2 . . a . . . . . . .. . . a . . . . . . . 52

Insect Vectors . . . . . . . . . . . . . . . . , a . , . . . 53

Control . . . . . . . . . . . . . . . ... .. .a .. . . 58

Trypanosomiasis . . . . . . . . . . . . . . . . . .. . .. . a 63

Schistosomiasis (Bilharziasis) . . . . . . . . . . . . . . . 65

Control and recommendations . . . . . . . . . . . . . . . . . . 69

General Reoommersdations . . . . . . . . . . . . . . . . . . . . 73

Literature Cited..... ... . . . . . .. , , . . . 75

Photographs . . . . . . . . . . . . . . . * . .. ... 77


Maps and graphs

Faith the realization that any major impoundment and irrigation project

in the tropics would inevitably result in profound ecological changes,

which in turn might adversely effectt health co-rditiona, it J.i considered

highly desirable that a survey of medically important insects b' under-

taken in the Shire River Valley.

The inavetitgtior originally planned for 1951, mas be~un with our

departure from the United States on 18 June 1952, and continued until we

left Nyaealund on 10 September the same year. 'ho dry, cool months were

chosen for the survey so that e -~ul have the ertAtast possible degree

of fleibility in moving about the country. 'uch movneaat would not have

been possible during the rainy season when m an of the main roads are

impassable and l-rge 3sotions of the country become inaccesible.

Lake Nyasa has been subject to considerable fluctuations in lovel,

sometimes falling so low that there was not sufficient water to keep the

Upper Shire River flow~ . At other tinee the amaout of vater carried

from the lake by the Shire and added to by runoff dovnstream has been so

reat that extensive flooding of the lower river has caused enoraou

damage to orops and ntold suffering by the native population. To control

and regulate the lewvl of Lake fraa, it is believed that a barrage built

across the river at LiLvode or above that point would be effective. In

addition, a das io envisioned either at Matope or at pataain~ where

electricity will be generated by water power. The third aspect of the

engine ing task is the development of a system of irritation canals nd

drain through the extensive Elephant Marsh and adjacent flood plain areas

of the Lover River, To aoom plish the latter project, it will first be

neesesary to channelAe and drain this hbeoI marsh area.

The timing of the entomological survi was unfortunate in aome reastota

aince the enginering planning had only really gotten a good start and no

definite plans had yet crystalized. Much of tho .ara with vhiah -vo ra'e

concerned has not yet been adequatel-y spped and it was naooosaa~ to

estimate levels and areas that may be flooded or i d-.L.-d i;' t.h~ co=sa

of the sngineering work. Some of our conclusions aly, thoxrfore, h'~a

to be reevaluated hsen the topoaply% of the country is better known.

We should like to ol'XAr our sincere th nks to all those persons o0

assisted us in ways too naerous to mention. In particul-r we should lik

to acknovwledt the koen interest and assistance of Mr. 3. 7. Rich-rds,

Chief Tngineer, Shire Talley Project, a.nd of all the member~ of his staff.

They smoothed mary pathas that min4ht have caused ua reat difficulties.

Dr. D. J. M. Hackenzie, Director of Meodial services, yteaiaand, *wa most

helpful during the initial stages of our work a le ;ia l.tidBO a con-

tinuing interest in our prooese. Through !)r. Macnaasio' a ki:cidnei, we

were assisted by Mr. c- jorge Hopaer, Sanitiary Inspector, Zomba District,

vbo ret ined witth us for most of the time we were ie n 1~-aalfard. :e -

vost grateful to Mr. Bopper, an aethbsiaetiO and int Oreat d coa-pnioa,

vho, through his knowledge of Chinyanja, and aowuaintni e with the people,

helped us imeasurably. Identifications of ZUn ikJ were made by Dr.

Paul Freeman of the British MUseo. To all the other persons, too may

to aone indiida4mlli who assisted us, we wish to express our deep gratitude.


O s~r rQy bad certain objectives which can be sumarized as follows

1. To determine the species of insect vectors of baan diseases

present in the Shire River Talley System.

2. To determine as nearly as possible the prevalence of insect

borne diseases in the river system.

- ) -

3. To d;'.teramine the Uiztribation .tdnd thTo prov'.nce of the

vt ctors.

. To dotrmino the :eaaonal relationships of these vectors to

the incidence and transmi3sion of thee d3ias-es.

5. To ascertain and evaluate tho ecolo'ica-l :a 1ociations existing

in the Shire Valloy Arain-ge.

6. To eozaine the relationships between the human populationn .ad

disease picture.

7. To estimate chaZnes that amght occur in the prov'~Ience and

breeding habits of the insects, provided itabilization of the

River and Lake T f sa were to occur.

8. To determine the problems that would be raiPed by the ohannbelizing

of the river in the 3lephant Mar~ h -ra -.nd the establi"hmnent of

s. system of irrirttion drains though this area.

9. '.ftnr a careful study of the entire situation to ma k appropriatee

recomaondations -herever possible asto te to 3te- b to .:en in

dealing 4ith the problems now existing~ and those tha~t may be

created 'by man-made changes.

It was unfortunate in some ways that the dry season was chosen for

this survey for we obtained a picture of the insect vectors in their

period of mini4nm ab4ndanc. At this time of the year breeding is confined

to permanent waters aid in both the aquatio and terrestrial foras repro-

duction is highly restricted and the populations are minimal,


We were fortunate in belag provided with a very useable vehicle for

our travels through the country. The Land Rover, hi rly adiLptable to most

typos of terrain, made it fairly easy to move about over the roads in

yas~Aland. Our-aim .,a to try to get to avery place on the �iver that

wi-- -.t ;ll possible nd to i to a no thf tributaries of the rivnr .qyt m1.

Je visited the :iiv-r w.herever athre -s a. road or A -ath tht i nt.r*-

oepted it. Most of �ar time wa, therefore, pent on th' hire ,:ro-er -'I

its m4aor tributaries. Aany of the tribut,:x*ias luring nid-1952 ,ere

floAwng at the time of our survey, and w- did got , fairly good idea of

the kinds of insects that mould ba present even duringg the operio oi high

rainfall. 3y the time -e had completed our stay and were road to return

to the United Statae, several of the strrams which vwe examined earlier

were dry. We spent a small amoont of our time on the southern shores of

Lake Nyasa as wvel, and were able to travel on the Lake for two i.qs on

the Like ,teamer, Ilala." Thia pe-rmitted us to examine the shore line

of the lower Tart of the Lake on the dest side. W'e wer also able to

utilize the launch of Mr. Seotmat , District Comi asioner, Fort Johnston,

for an examination of the uppermost parts of the 5hire river where it

drains Laike Syea and the southern L~-ke shore, both on the aat and on the

vst sides. At anoth,-r time w oarised the river by launch from the

Halwarov oap site at Ntundu to Lia*ondo. 'o investi.ated the shores of

Lake ailombe both from the launch and at several points whore it was

accessible by road or path.

we were able also to examine the lowermost section of the Shire.

Mr. Lopes, owner of a large cotton plantation in Portugese 3aat Africa

at Maassa, was kind enough to lend us his river launch, the "Piri Pir, A

in which we traveled from Port Berald down the Shire to its Jancture with

the Zabaesi and up the Zambesi to the toiw of aturara,

Thns it can be soon that we were able to covor nearly the entire

river system the southern and of Lake Nyasa, and parts of Lake Malosbe.

Time was also spent in working in the Elephant Marsh area to learn something

of its e olog and to collect insects.



The details of our itinerary :.nd schedule ai r shown belova

June 25 - Arrived B31ntyre

June 26-29 - Limbeo (mSing arras ements for trip ..nd
getting supplies)

Juno 30 - Zomba (aeetin; .ith :.'i. .)

July 1-3 - ltundu-;'ort .Jo4non ..r-A

July 9 - Ainbo (,entifyi.n ipe clnens)

July 10-15 - Li (.oe ( orkin:; cholo, ptaaEr~ , itop ,-s

July 16-29 - Tenada cam n -.1 CObiromo

Jualy 30-n.ugAst 3 - Limbe

Azeasat 4-7 - Traiveing to kota Iota to bo:.;rd HIla. rAd
two da voyage on the ship

Augst 8-12 - Ntuadi -Fort Johnson area

A swUt 13-14 - Limbe

Aiuust 1.16 - oimba area

August 18-20 - Limbe (uorkina Mlanje -r'a)

August 21-26 - Port Herald (Augst 23-24 Port Hersal to
3utturara by launch)

Auu t 2 - :chaula~

Amataat 28-3)fpt;smbr 2- Limbe workingg ;~lkera ?eaPrry :ni !pataaan@a

September 3-4 - Fort Johaaon intervieww with Dr. L-mborn)

September 5-9 - Limbo (identifyin and packing wipeoimena)

September 10 - Departed sy.saland for U. K.

In nearly all oc"ses we were afforded the hospitality of the field

parties of Sir William Balorov sad Partners and were thu abla to avoid

the oam of bhaing to set up our own camp.

The locations at which we examined the river and its tributaries are

shown on map 1.


The ay~;.saland Prote ctorato is a narrow strip of .3st-Centrai ifrica

with north-south oriontAItion .--d an rea of about 37,800 3s:are ailes.

It extends for somo 520 miles between 90 451' -d.. 170 16' aouth latitude nd

lies between 330 and 36 oast lontitulo, aruJi". In -.iAth bet ean 30

and 100 miles. Its southern tip lies about 130 miles from the Indian

Ooean. The southern half of the country is bounded by Portu,-gtse !oast

Jfrica (Mozaamiq~g ), with Sacthern bhodeeia a'wove this on the vost and

Ta'-saB on the north aind northswet.

Seaouse of its slight width the pGyiorapy of `as-alamd is mostt

wholly involved with the Great A.frioan i-Lft, which extend for 3500 miles

from the Sabi -trer to Asia Minor -aid contains most of the grat African

Xlaes. The chief topographic features 4re (a) the arasal-~n l egment of

the rift, a long narrow depression occupied by Lake -lraa and Its effluent,

the Shire pronouncedd a~MMrg River, (b) a series of inmotains ad.

plateaus flanking the rift on east mid -est and ranging in elevation

from 2000 to 3500 feet in the Sbire EilibLnds to ths south, from oame-

vhat higher in the Niskta, "afinga. and Vipya uplaunda alone the vast side

of the lake and up to 8000 feet in the ~ tyika Plateau in the north, Irom

the southern hihlab1 ds rise the isolated assifs Zomba (7000 feet) and

Mlaaje (10,000 feet), intrauive masses of syenits that have perforated

the surrounding mztamorphi o rodka. The loet pint in the protectorate

is in ZIover Shire where the river d osses into Mozambique at an elevation

of about 110 feet.

Besides the great Lak2e rasa there are two smaller lakes (Shirwa and

Chutta) lying out Ila the Sbire-~rasa system on the Portuguase frontier

to the east.


To b: aemennt rooks of T.3saland .-ie ost3z scOhists ad. .nai3:3esa of

prme-Cmbriar orsiin. There aize s-c:ttered rnito inttmiti ons such ;a

those that formed "omba and Manej , but 1 3nit. is ~?oly found. The

renit te twoth ~s to produce soil t:yies diiitlrnct frcm those on the more

basic rock. of the country, rfnd iLn C i biooical invetiptlons we woe

integrated to find An almost oRmpleta lad of srais3 in the *--ction 0f the

Shiro aitcahient orLignating on Mianje.

Oomtplarl interrelnted .,ith tfhe bastcannt series, w.i:c. includes

a high proportion of poorly iiffere.nti:.ted rocks of intermediate structure ,

and in places intprfolded 4-th them, 3 --mother, younBger Froup of sedimantra7

schists ii;n pyllites 5cosy. ?s the M~fin.! Series, *-.hich takes its name

from t1h tye locality on the -orthern Rhtdeislan. frontier. Included in

this -eries 'r -saome .-neicses injected ,;ith po.gmatitc feldaine�, i :rn.ot

and magnetite bNmadiin occur. Similar to the Mafjrji rocks, tbut Lth more1

olorits in their corpo.ition, are the roc~k of the t achipor ae ria niaed

after the achipere :ivWr in the Port aoHeraid ills and eaxtendina, into the

Zaabesi Valay.

As is often the case in Atfrica, above the basement complex t2hore is

a Arked break in the continuity, and the later geology of Myasalaan is

largely the biatory of the continental faulting that, .during the tortia-y,

mdle the rift valley. The accompanying stratlgraphic time scale adapted

from cooper (1947), sumaarims the main geological fee-tues and events.

GolZara4fl M4siA A 1=Ewrfstalnd

L. FrmAation ar emn

Plaistooene Dvangwa Oravels
Songue Alkali e Lavas
Ohiteawe Pebble 3ode
Chivonde Beds (marls ;ixl sands)



Lowsr(T) Croetcous



St=ai Pebble ':u!r'tones (North 2Tysa)
Intrustions of ultra'aniic zzko.o 3a -Ipea
(Lo0- er hidr e)

Intrationn of !-allin"-. rczca, eph.elIne ~ernito
snd lypalvsaal rock
Ltpata folding

Dinosaur 3ods (North Vasa)
Lupata Series (sandatonea :Ath rfyols and
alkaline lavas) 4
Chila Ooaplex oif 01a�heline--'nite .ard
rIVOlite pipes
3lock faulting of Karroo rocks, with ?ydrothermal
intrusions of uarts .and rhyolite

Karroo ysteO

Red Sandstone
TUper S3n=stone

Lower 3aWufort
Red Marla
Middle Sandstone

Shale @roip
Lover 3andatona
Wmansa shales

KNafin Serioe
o hipere Seri e
Bastc gnsissio coTplox


asailand haa a m osooa liaate, with the year diUided into a smer

vet season and a winter dry season. Because of a seasonal shift in air-

ass relations the country reofive, moiat air for one-half the year and

dry air for the other. The ragalca atner rains oome whan a northerly

airstream ta's the saturated equatorial airmass deeply enough to furnish

a continuous flow of vet air into the ocuntry.

- 9 -

The rains usually gin in Octo ~r n.ud continuum until :ay, :'though

most of the r-in f:49 ll'A bt'e. Leoember ;a.r March, i.n in -omer year' tohre

w y hb none at all unmtl )eoemnber. Thare is also 3om!times a slackening

or cessation of the rains in Janary. Tbhi little dry season," Ahich

m*ey causea *rant daaige to crops and ve.Qetation i3 probably correlated.

with the p~.asing of tho gun into the southern hemisphere an. thfs mea

represent the dry interval betowen the trouble rain--the "long" a'-nd sortr"

raine-of ecatorial regions.

3eaanse of .gr~at differences of r.lief A'thiin narrow confines, and

of the stability of tha prndomina nt planetary winds, '3asalad saou,

arkeid gooraphic aWnd topographic asriaticn in both ttnetparatre and

rainfall. In giera.l thore sy b-e ielnimted a met northern and of the

country, a ~cderately -t soutlihrn nd .!.ni -' d y iddle. This lifferentiation

-old not b agviaent in . 'obr t.atal of - vrage ra l E n 'ecipitaticn values,

since the Lower Shire sally has as li'tleZ tot:.l ri rinfal.l as lmost aM

section of the Protectorate. In the north, hotOvr, the yearly total

rnpressnts the rnin of fowu to six months only, thile in the south the dry

season is usually ameliorated by periods of gry, driazly weather that may

last for six or eight days and during dlch the evaporation rate is lowered

and some slight amont of rain may .all, asually in the fora of "scotch

mist" or very light gnuty saowe s,

SThese storm are called Ochiparonia" because they appear to emanate

from an isolated mountain bi that name lying southeast of Ml.nje in

Portuguse territory. According to Johnatono (1949) they are actually

due to antiyVolonic movements that set up an airstream that is moist

in winter (and dry in squmner), .ad vhhen this emergos from the Iniian Ocean

and rises over the land it condenses about auch mossif as M Chiperoni and

Mlanoe and asems to be produced by them.

- 10 -

Aince 3ome 3ight percent of the country ii above the 6000-foot

contour the tritltaries of th.e L.a -TaS-JhtlJ l ?iv r 1y-te0n *eaive

a fairly rlii.he mp3ly of rmin in thoir hl:..dwAters .-;i ther.- ;zr

mon; them n. member of permnant trer.s. urir thJe -t ZoasuA Ziors

occur, '~ich = l' result in violent Ioo2.1 lA.loods. In 19'5-14., 10

inches of rSai fall 1 a outh :;1- . in 2-, hours; '.n-i the cat:,strophia

Zomna flood of Deoema r, 19.6, rosult -d fro a' rinfaUl of 26 inches in

'10 hours.

In ganerea temperatures are -ot tx*reme, *Tio hottest weather occurs

Just before the rai~n break in Nov-.D. or D cem r, vi. h the Lower hire

Ifa be quite ,iseea~ Jl, With tem.c raturi cno B r rising -bove 100

degrees 2aremhelt. Mo1 t ot the ccLmtry, however, is a bov tLh 30C00-foot

aontor, -ihich ')ebenhxn (19Z) c-ll � i- ''-health contour' for /uropeans

and hare period~ of hiJb tape-rature .zre .hortlived, .nd aich less ire.uaent

tha- the times wbhe ona 2 hi4ors front the a;ill.

The vaeetation of ae&asaland1 is lb r.g�el of the monsoom forest or

saranna forest type, coposed of oren woods -ith ~all to medium si-ed

partly deoidwou tree with greater or lesser expanse of :3ort or tell

grass beneath or separating thm. Th3 most -idespread tupe is a S3zaclsteg i

aiombo with varying admazture of other trees. Azonal types include -teppe

that approaches true desert in scattered rainshadowan, and th moist, cool

Caller and fringe forests alocnt the watar courses, ,.ith closed cpnopies

and the look of true ri4n-forest . Trua climatio rainforest apparently

occurs only about the eat northimeterr nbhore of the l
etde of leanje, wihea- rainfall ran ' e vell above 100 inches and there is

no re o dry season.

- 11 -

Lke ESyaaia is the third l-ru;eat of the Afric-i.- Pl;:'k - . theo ourth

deopeat lai e in the world. It Occt:ies . sa~-'~ow, trout -llke .cti-n of

the trebt rift, "bing 350 miles loi=. :.ni btween 2C nd 50 niloe wida,

and covering; ni: . xsio,. of a.louit l,00CC ;iu'c :.ilan. he .misfce c.' 'ha

lake is sonevwit more th.n 150CC rfet :.Lov' v-s lvol, ,i. -zt tt tle t pos

point (2300 feet), wA ich ocourws t.- tho nort'rn rnd , t;le "ottcm i :,one

700 faet brn.ow see level. The s;orelino i.i zontly precipitoas,t the

fla.~kizz ount"jix and platosuz risinrg ,aptly at or n.ar the 3Itzr's

edge. At tho -,outhern ond the "hirl..ni t-a f'rth -r 6ck, l-iviazn

borderinga owlynd, thm marginz 0o -hih are) Ziltraitely flooded .ia

draiaad by the strong flcan tiosa 1i laki-e l;.Vl.

Despite a dearth o.f aheilvi.n :i'orO for breeding-rouind, the .9xtr m

clarity of' th. .watr, .nd a lack of .in. iovd, oy;en below -1. death of 100

feot, there i n n an rortant and potantiall extremely vu: ilb1l fi:jry,

especially Lbot the southern ond of the Lakc. 'Thi V aa i i-h Zi=ana

is bioloicalir ona of the oat inte ti in i tCh entire -,orl.', i.ith some

87 percent endanmim of the moet extraordinary sort.

As the most conspicuous physiograpi'4c feature of a,-Al.and, L-mk

rasa has been of ageat importance in the economic development of the

cointr , bmt its value in this respeot has been keep it a miniamu by

a lack of good harbors along the bold shoreline, by the frwquenoo vd

violence of squall and storms and by the freakish tIluctuations in wpte

level that make permanent shoreside instsllatione iapreaUiable.

This variation in level is the lnae's moat eaoontrio und atrikdag

feature. Although anmnal chance, idus to differential ~,sraonA l infk'

and evaoration, cause a rande in lovel of some three feet, this l- rIat&t

is completely overshadowed by a long-time, perhaps oyoliU, oh~nAe Ar fte

- 12 -

order of 20 or moro feet.

For instauce, according to ,rnold (1952), the level on the Fort

Jonaston gauge at the southern and of the l.4e was, in 1912, two feet

-ight inc :e, while in 1948 it stood at twonty-si= foott three inches.

Although the length of the cycle a-i evidOntly be too reoat to

permit its conclusive demonstration from available data (readings go

back to 1859), there esn be little doubt that dich a cycle exitsta .-

that it is of 3ud% a scale as not to bo disruitod by nvon such phenomenal

rainfall as that of 1945 and 1947.

TMs flucItEation hia yestly imped-oil1 t ea evelo-aent of la1ke tran--

port, since jetties And docka are topped or -traiadeL by tlhe extra

of the cycle. The phenoen un i likewise :a obstacle to the stailization

of a fiheriea industry in the hijrly ro.lctive -louthern and or the 1ae,

since the rioe =!i f�ll of the w;etar ihift ii dostrWo the .ones .uit&ble

for nesting .ctivity. It :lso floods atandinG timber ther oh " hich the

Africaa fishermen cannot draw their seines.

AS will be explained I are detail ri n a later section, the incidence

along the lake shore of the common vasting disease, bilxrzia, is directly

correlated with the stage of the cyole, since the bar-laoon structure of

the emerging shore brings the lake people in contact with the stagant

longshore lagoon water, which provides ideal conditions for completion of

the life cycle of the bilhersia parasite.

The principal factor in controlling this crUmos ayclic rise and fall

of Lake agas& appears to be the character of the outlet, the Upper Shire

River. The lake does not drain over a narrow, permanent lip, but rather

across a nearly level plain of recent and easily erodable allu isv, and it

is reasonably believed that the instability of the lake level is largely

a reflection of the impermanenoe of this single outlet. Some of the evidence
for this assumption vill be shown below.

- 13 -


The ;Shir-, Rivor anorgs fror.i the 3outlern and o0 L9co Iyao -a ibut

four miles north of Fort Johnston fla flow. southard to .h'i- the :%abesi

in Portuguese reast Africa aome fifty miles south of Port Herald.

The profound aieates of the e hlnin la~ke level on the character of

the 3h4re--ospeci.lly of the Upper Riv-r-mC y we seen in old rororta t-at

beai on the n.vin~bility of the stream in former times. .-t the time of

Livingctonaes es-plorations (1859), for instance, thb Shire Wts refa.rded,

as a highway into Central Afrlta, .freely n;vihAble by good-sized craft

for ita entire iengthi xoept for the middle rapid;s section, where a 50

mile port'ae -&a re-U"ired. Of the condition of the Upper -ire lt that

time Livingstone wrote3 ". 'ter passing the l -st of the (tu'chison)

catarscts w-o laomched our boat on the lroad and deep -a-ters of the Upper

Shire and -ere 7irt ually on tho l ke, for thCe ntla current sho :~ but

little difference in lavel... The .ntives rr~{.rt the Uppr Th 're a

prolongation of LU-es .yaaa.'.

Toc'urd ths and of the last century the falling ; l:1e level so reduced

the flew in the chiro that all traffic by frei ht-c-arTying boat -as out

off in the Upper River.

As was mentioned above, the instability of the lake level is largely

doe to the nature of the outlet, whioh is an outlet-in-dopth, flowi,

with only a few feet of fall, for some 50 miles over its oit deposits and

meeting the first hard obstruction in a ridge or sill of ieiss near Liwonde.

In a sense this entire reach, comprising some twr-thirds of the Upper

shire may be regarded as an extension of the lake basin, since there is no

point anywhere along its eouro from which the lake level is permanently

governed. The bed is alternately silted up or scoured out, and during the

past half-century shallow lakes and embayments have growa in the flood

- il" -

plain Ind waned :atin as bara and sudd dam h wv obstructed the channel

for a while 'an then been cut awVay in. The flow hai for lon:: fn riods

topped completely, and on at lenot two occasions h,- been * wrs.

The set of factors resulting in the lIt -1r- o Ayciea r i:z .ad

fall have evidently been the ev'ntnal ov'rrtopTit 4 :L ,! srofion of i

gradually formed bar and idd barrage in this sloly moving outlet reach.

Emtback (1948) located four birs in the river, a follo's

(1) 'A ;ve-btlt sand spit 'ith nortirwe~t-soutih~est trend, blocking

the "outlet" into the ;hire.

(2) . delta--like bar 11 riles :0-1otr:'e at the ,nttrnnc to jiko

N3lombe, ;n embaymrn-t of the rit'r at prte.sent about 19 mil-e lorw., 1C

miles -4doe .ad 12-15 feo t deep. e-ouseO o' the slackonim;: of the curarnt

-ihen the rivar entered this lake a-n Munta~le "ilt-bar cn.m usually fodi'

at this point. Moreover, the lak~ is an in--oortant Aite for the formati~

and launchi n of the 3add and ltoati1g-ls.1s.nd thlt often block the river

lower d.o'a,

(3) i4khazi bar, located 37 miles bolow L."- iz s-s) jut bolow the

village of M 'er at the outlet from Lako 'alombe. Here the inte rmittent

but seasonally important SkWasi brings down hes aaounto of silt from the

western hitnhilada during times of hravy rain -nd in its siXfting delta

deposits interposes the first najor obstruction to the flow of the -ater

from Lake asa. In 1906 and 1907 eaoeptionally hoevy rains in the headp-

�.ter of the has~t daamed the Shire with these delta deposits, and,

ugwented tr aooaalation of sudd formed in the slack water , blocked the

flow from the lake during tho years from 1917 to 1933 and left the Loser

Shire dependent on its tributaries for all its water. The subsequent slow

rise of the lake to overtop and begin the erosion of this obstruction

initiated vbat will probably be a lon-term period of generally falling


-15 -

(') The rock b):ir at Lin-.ond--the molt ota nbla and etr.l eoant factor in

rgulnti0; tha' -;'r~ .diant of the ri-3r to thiL -point.

t. he aed o02 the ihit o lhnd s it'1lf to .u'Sivition Into th!"o oTbvous

sections the Umpoor hi4:r, frou L eike N I to '.toape; tl7e M il.es ",

frca M4atope t.hrou h the .;eribe of rtpie in Ah�o.. moSt of the iJop 3*.'ae

the lke= -t thea Za.besi Vallay oacur , to tho foot of urchirion Yall.s;

:ad the Lower Shi�a from the fcot of t e 1.at fa.ll3 tthe S. ibeoi.

because of A comb-ina.tion of oolo:ic.A. an. = i ;torical f.tor3, ;it:i-

bution of t$lo f10amn of the river is correlated to come aztent with these

three a.ivtisions, -althowu h the only re-ally trenchant zoos;cogr-rhtio se-rorttion

th-.t has been noted is the s-paration of the LaMko Syaea fish enderiios

frcn the amb!asi fnna -by fast-water barrier in the fiddleo 2ivcr -orgea.

'The huae 'of*Ahell turtle, OvrFrP. occurs in the upper rivTr -nzd

not in the lower, 'ut ur-ly 1colosor-c t'actors ast in this cae be

responsible, since the animal ooowus 'lso in the anmbesi. �-one the

saler -ad. more readily-sproadinu inverqserates :q -o-aphic seir^-.tiani

is thea hire Valley is oeTrhiadoved by o
ment :alon the course of the riv'-r nd across its valley acvctions.

On physioga~ hio and )ldrologi ground Griffin (1946) divided the

river into five roaches. His scheme seems moderately natural, except for

the possible need for further eubtdviaion of some of his sections. Oriffin*

divisions vwre as follows

LteA rAlh. Lake Wasa to Liwtrde; distance of 50 miles, vith a

fall in level of 5-6 feet or lots. A 20 mile section of this reach is

comprised by Leak Halombe, and here the waew action along the exposed

shores and the Vast bordering expanses of drmbo (grass mnIwh) and of

reed-& hoced lageoon-filling mait seem sufficient basis for regarding

Malombo a a separate subdivision. On the other hand, as was mentioned

earlier, the lake and all the river above it, and perhaps also the river

- 16 -

below it as far ns the LiwDonde sill, could be con.Adered -,art of the

narroAwing southern eiav of Lte |asr3.D

aaam rMhC. LU-.iove to nuer HKtopa; a di.4tcrca of 25 mil-: -ith
:I f.ll of -liUhtly more th-n --. :oot per diles. Thi tr th -:?ceding

oonstitute the "Uppr .hire."

W HMatope to MWy.;ana at the foot of Mturciioon a'-s; a

*ditance of 45--5 miles Aith a dron_ of 1300 foot. Much of the bed here

is in rockry orgoe ~ad alutoa-1�io tro-uws, Aith fz-ls and. -_pidfs fre iOLnt

but with occasional reaches of smoothh quiet flow.

rtryh y-Zg MUtennza to Port. r-:ld; . instancee of perpris 35 to

95 miles, :ith a .al of scme 10 inch ls pr mile. R-re on the Lo'er

Shire Plain the trirea flows aoothly ad r-apidly. 'or abucit 20 milas

the channel is 'ell dlofined a~d then r~' -lly tlh bSanms r lost in the

vast, flat, partly filled liogon ikno�-. as .1e^rxnt Mar-,h,; -whcir. the rivr-

atvaners ngami s hfts its course among multiple czh-mealz l di'tributarios.

At Chircao the Shire receives it-s most important tributay, the Auo, which

ari.ees Oa the :uo Plateau on the southernn face of Maine, falls 2aundri a

of feet into the head of hio Gorge, piAcks xup various tributaries from the

Mlanje watershed and then floev southward, foramin the boundary between

Nasala nd and Portuguese Africa for it a entire langth. ITh windtierd aide

of Mlanje receives the heaviest rainfall in the Protectorate -ani the Roo is

a factor in the flooding of the Loe.er shire Plain.

2.h1& e k.h, Port Herald to the Zambesi; a distance of 50 miles.

This reach is well within the flood levels of the Zambesi and -shov

backwdter influence for its whole length. During the disastrous flood of

1949 the Shire was badred by Zam=bsi water as far upstreaa as Chiroaao. .a

the Shire advances into Mosambique aind the Zaambea floodplain, diita features

appear and the distributaries move across a broad expanse of alluvium between

high natural lavee.

S17 -


3:; or -tn -''M.a (19n7) in thir tEport on the i -(1947ton lilri' tion

of ya.malrnd eliae t that the ounitrey ha the hijhlst . . ar .a aaayer ofl

People per sq,'- e ile of any c utry in ~uteast-centrnl rica.,

.ccord in to th$.s �~uthors thtre *r9 40 .5 person-j phe square -ile,

while, the 190 can~e~s ttribu'f~ea t ptaso-~ s tu hs s3ur ' mile.

3a4tr r anS 'hitote atate n tlht the hi hl: . -iot *at of te lo-isr Shiro

iLestr h tve tie = tjor concentration of population wAth thb bSlk living. at

an -altitude of 750 to 1000 metrs. nr-ey oonslder the concentration -is

being a response to va heltVy climate -:nd good soil .and -imter. 31s:t27a

and 'ZoInba .re the chief areas in ;hich the h4iites -iro conoontrated, dile

the Afrio-ns there number about 500 pnr s -i? ile. 3alo chir tlikwsa the

density loo-U.y noaoeods 3CO0 per scare mile. To the -iest of the Shtir

valley, the density ftalls to 100 per zIquLr�e mile from &estAra scheu

district north to the southern p-rt of the Zotm--ot- dis-trict. ovrthw-ards

the distribution of the people is spotty.

FZrom thii report , it omn be seen thlt tahe .-at5:st p-art of thls

ryaaaland population is concentrated in the area affected bry the 3hire

Valley Project.


PMalari i~. one of the most a2)ricu - roblema confronting the medical

department in le-aalnd wbire the population is alaoot universally infected

with the disease. As far a� v we hlv been -bl to deoteraine, there is no

detailed knor-ledt, of the incidence of the disease or of the parsites

that are present. To date no comprehensive furvsy3 havs been maie. There

have been, in the past, occasional limited studies of the incidence among

school children, but these suveys are tot-al.y Inadoe ua to show the

true pr>valance and the true sffecta of the disease on the population

of the country. That the disease is almost universally .present, however,

all medical offoiera ith hom ws discussed the problem fully concarred.

That it takes a tramemndo toll in :3pping the vitality of the p-opl is1

irmqu~ationed, ~daid tlt.t inf".nt morta.lity Is tremendoutl affected b'y the

presence of the lsoase is Also .'.ck o'ejdged by the nAedical people.

During & brief 1iScuseion of the prcblase with Dr. G. wioLean, UJniversitioe

Mission ChriStian Azs-ociation, Fort Joiaston, we -*ere told that .laria

is the gre~tpet scourge of the country. )r. MacLean estimated that xifant

mortality dun to alalria runs in found fifty percent, although he -was careiu

to note that he had no substantiating data to support this. As far as

we can determine, no vital statistics are kapt on the birft and. death

in this country except in the urban centers. Obviously then, vrnder sach

circumtstnoes, it would be impossible to msle any definite statemonte as

to the total effeots of this debilitating disease. Its importance, hoyaver,

isu nquestioned.

e have examined the records of the Medical Department through their

published annual reports from the year 1920-1950. One of the most

obviaws conclusions that can be drawn is that the disease, although

rco~gnised as of major importance, bas been sadly neglected.


fhe first important reference to .nalari i, in the 1940 " uarnal

Report of the HMediial Deprtu ent" whero. t 1-i ptclro d out 'th.t I5:3

of the .uropei Kul ti^t aditted to ho4pit";l Qe-> in'ctc;'ld t,-::.. .

Ao contimno, the 19nL1 r p1ort 0'vrs ho fin , u -..s to c . .-o :..-:Cc o '

mslaria, oxcpt to -point out that no r:t o th. co2 -tr: 'n; t o~:

the diae.ase. Thea nsrne ia repnsatad in the 19 2 h rort, ?b; 15-3I :o'st

i the firit one th.t furnl-hes fi.uror of a.y hijAnifiience sttLing thit

13,255 -Africans ni 316 et d europa~t a d ens t: td for alaia. The t;9 G

na_7lari.a *orm not noted. In the 19.'J4 -sport, the statement is asia tlh-t

"rmalaria remain-; the most iLrorta;nt of .sll - !ieaaes." Son-'urocea cnse

fell from 13,255 in 1943 to 12,50' in 19-;, 'but urhoea c--ses i'cra-se(d

fro 316 to 322. In 1945 the re-ort ag.in points out that ala ria i;:i the

most imTortr-t laftctioaLC t ou r z 'rasitie i.aase wi'h -7.r o3 *11 oes

treated being -.ttritbutabla to alari. and 18.7 otf -+ e dezath- birn.

ciaied . by tVis tisease. 39.6' o- '.- ' reopen .- ito t he ospit l

had mal xria. In th 19w 7 're rt there 1i :n -S-.et to b,.;: t-ic:f '

malria 'by typsa using the comnon w-aE daerie atlonj

Senidn tCrtian - 213

Subtertin -- 134-1

b4zartan - 4-

Cached -ds 78

hoblassified - 1776

In 1988 there is a significant increa.3e Nith 223 :uropeans =ad 25,127

Africans being treated for the disease, and 48 deaths listed. The 1950

report, which is the most recent available, to us, pointed out that there

were 36,984 oases treated In hospitals and out-patioent dep*srtmente. Here

again the canes .are broken down into t7yess


Benign tertian - 1152

Subtertian 8194

uat~a - 4'2

Uncla .sified - 27,553

It is Perfsotly ciear on :lainctio: these trcords that cly a

J.all fraction of the po oulation is aver treated for iidaria. Undoubtedly,

if the disease wer-e treated in all of it- atspac-ts in -ll of the country,

the medice- d ipatment 'ri uld be totw-ly ia 'euate tc -andle ttc he .itAation.

.Ad.itt-dly this is a bleak picture in so f'; as the problems o.f aalaria

in wraesaland are concerned.

'1i0 chaei that oar likely to be broad t about "'r t4he enginring

aspects of th ThitR V.alley Project rill cartaixnly wr~ate more pe~-ranen

broadi� pl-oss for tho -cetors 31 sflaria ten terh ,ar 4owv *_1 ther

o' not thiA :..ill affcCt the m laia incidence is open ' .o estion. 4ith

the umnivnrality of the malaria there is little danca of - - u.tor

number of people becoming i-fected: xoev-r, iher :.'ill be :;r t -c.tc

degree of tramemission tIUouhouut a1ceh of th� year coroe uont ton G`hsa

engineeriwa change. For tfhwt reason, wLiaL Iust be considered s

the zvaer one lisesse from the medical 3tardpoint that amut be dealt

with in o~zuiating the problems that vill be created ~t anyv colocoal

changes in the region,

Nalaria h~s long been recognized as e. problem wherever xater is

iapounded in the tropics. Malaria and ipoumndment have 6een dealt -ith

in aay previous rpblicatlons aad it has been shown repeatedly that

unless adequate measures and intelligent plannLSn are taken prior to

these engineering changes, that great d-aage can be done to the population

of a country, and that the expense of controlling, and eradioatinm, a~sara

from an area after the construction is completed is far greater than to

build malaria engineering into the project.


' y1tLJr!.aead lhs nay l bo important i.r.L- yuctors; 'owino , tho

lijtri'intion of thoE ss l Aniy iCs c:. Dtit I na' or rtui rc,.oni o A
both .-e w.: -:nt Zhro'ghut Ci ye . .ain popu Atio- oa r.o o .i i

$4ll, the oltle ;picieS t 'rdi:. to rise, .. o pcie tht - cC

i-aport ;aoo ;in :azlarisA tr?.T.:;3;:'i..�,ion -s1 .npl.A ., ^ .ilei a

ncgrnb>hf l mBt&is. 1.Ail.i. In i^.iti.on to tiIoei spociist o. .au'lr-1 iia

othr;2"3 var kno- a'.roa the countkr7nd rL a isj considered to b'- of :e^-,1.

1;orr:--nce fr tho ont o of .isea tr ision. The othir lzo-wn

pecisa ^of malaiai.. imaosZduitoes recorded i: a;
3 aove records, t�oznaro Joai t r ob

Region," b7 Bothin 3414illon, p~illshed -in 1947. In aObltion to 14

spo�sa, -we *in add to t nis list ta others, Aaqb
:ew1 =a rt+r, nd MW 'Awards. 7or the puObrposo of th�
at. l mndalgth c
remrt vs :3. hadscs/oniana the to iportnt vctor,
Sndation t other Aiia is

A. GntnerfinB

A. TrhnanZai.a '-^hd0^

k. ar3SmaS2 "heo'Jld

'Zhe aiove re aosrta, -xch^aiveoet- a ^-w- eenstani-- SS ni-: '^o 0btined

fre of int rest pubicatirfn, "The Anodpheint of tho r vauioepin eov--apcal

aegin te overall oth eillon, uthe Insects in 4Nyasal. n as regards their

species, we ekal add to thia list two others, anphlalftn istinctnatu

Newstead *a.n Garter, ntod. A. arAA.li ;Aajr-da. For the parioses of this
at length
report we 3hall discuse/only the two important milaria vectors, i.

asyichi'a f nd. itmenin. A1l previoua indiCations ars that other species

are of interest orimaarily from the atanidpoint of their ^ralu in dievylop-

ingi the overall lenovwledge of the ilsects in Nyasaland as regards their



pr?3oenoe and distribution. '-t somo of tBhe are of ifipor'- .tsee i.a

diniase vectors is .*Q yot unIproved. i2 1�i beei ani
some of the foorm azy be alrii vec tors; however, heir i~azort.cnca

in thiI o .paicty ta zo cv-r:.Adiow iy thae .raeenco o- i. :sJO ijn

ad i& f un a.R u _ tht to fall int,,:nto .:.n: .-" one.3 they ?rE.n " i...j, ; .

*.ny of them ol- yieli~ to control i-'es t it ~i,;t 'e 'ir -ut

to!-rd ae control of thoe izj.ort-. al. vectors. Thet ii el.r oi .I

true in t"h control of I. .-4paW.WAf . Of thoso apecioe in t;^i Za'ove list

., :rrp haS been incrmin.ted. .a . a1aiaiaa .e to.a of mcru ivtport cf

i L-;Spt ,-h.re itt) in"f activity rate ;--,: rather h-i "; hocv-r, i . es

..fri ca th i.dlic' tion is that ih species is of no i~ror ;ia09.

Diinj our :w 0."; of t,.hre aorthe ir. ?7.=-3i'-,-d, 1"f tho :p-Cian

lived hbovc, onl. t}h followi4.' -- ,ir cll3c-t in th .ult s,- a

not -jur.-ri3iL i. via:: of tha fect h tha ity -as .:j tct-, . ig

tho period o-" .~drl :r.iath--r, hke n 1:'-bit :t; i.. .;.Iyich tlhes for-a mo;.ar-iy

occur 'v~er- a:Ctraemly litated. it has lon been :
are sharply reAtrioted in their distribution depending on the cii~Ktic


Of the species that vere tzken, aoxlusive of .. n ifnn atna.

A. iautntti tena tbo'h n as eby fb r y tha :ot %i axnd-nt, ,]ascially as thia

true in the Lower River section, where, at hizrono and at Port Herzld

large nabers of tbhm were attracted to the screens of the living

quart-rs sho4y after dLark. DeMillon iL his re:ort on the 'thiopiaa

Anophelisn mentions that in Porttasee Sast Africa enormas naberb of

aVults m-y be produced in dansely ovrrgrown shallow swiaps. -uoh

condition also pertain in the Lover Rivr alley of the Zhire; especially

is this true in the Slephant Marsh region and though. the adult are


sq vary numerous, r latively few of them bite. De eillon further points

out that in the entire oargtai group the adults are generally regarded

as being zoophili a nd of no importance as vectors of malaria. That

they ;are important as indicators of conditions that :.re conducive to

the developmFnt of &. funetna, however, is of considerable inport-nce

since the two species occupy similar breeding places.

A. v~rtmr li is likewise rewarded by other workers to be of no

importance in malaria transmission. Its presence is of importance in

that it, too, serves :as an indicator of conditions favorable for the

breeding of Ad nt -A. rhdseiansls deserves more consideration.

It has been reported from Itasaland by Dr. Lamborn and hasI been shoan

to be a potential vector. This species should be investigated further

in iyasaland in any long term study that is done of the malaria situation

in this country.

A. tdesinin has been reported as being infooted in the laboratory

and there have been cases of reported infections in wild forms; however,

the scarcity of information about its natural infection are indicative

of the fact that the species is of little importance as a transmitter of

malaria under normal conditions.

A. d~fLlll is apparently of no importance as it does not normally

feed on humans. A large number of dissections have been made by various

workers but none has been found infected in nature. This species is

believed to feed almost exclusively on domestic animals when the adults

are found in the presence of humaas. A. aezllant can be considered of

no importance as a malaria wetor in the light of our present knowledge.

&. alinrZ Is another form which apparently does not normally feed

on man. The adults are very rarely taken indoors and when found in the

presence of man have been feeding on domestic animals. Dissections of


wild A. Aijnra_ have produced negative results with record to malaria.

. argtorienis is often found in places -hich may be favored by

. -ajbiQ as well as occurring in situations inhabited by a. fnn.atnn.

The species is generally regarded as not feeding on humans, although

natural infections with malaria have been reported. DeMeillon points

out that "its importance as a vector of malaria is probably slight in

the presence of mbiae or fne~ ta but this re iuires investigation

wherever it ooonra."

tha~roena breeds in places in which c. fAnestna can also be

found as well as under other conditions ndl it appears that this species

is potentially a dangerous form in which natural infections do occur,

although the evidence is somewhat conflicting. A. dthr nala has been

found infected in some area and in other sections dissections have

yielded negative results. The conclusion drawn by Dr. DeMeillon is that

the importance of this species in the presence of -, Fambi~s or funata

may be inconsiderable; bhouewr, as the nambers of the former two species

fall, then, and, as conditions are made suitable for the survival of

haranain. it msy have to be taken into consideration. For the purposes

of this report, this species will not be dealt with further.

A. snamrtan is another species that has been recorded from Nyasaland,

but was not taken during this survey. It is partly, or almost entirely,

zoophil i in its feeding habits. No infections with malaria have ever

been reported and it is very unlikely that the species is of any importance

from the standpoint of h~on malaria transmission.

AnhA1ba. l RmbibaW Gilest A. nasmbna has long beefn known from Nyasaland

and has been incriminated here as a malaria vector through the work of

Dr. . A. Lamborn, who has studied the mosquitoes of this country more

than any other person. Undoubtedly, at certain times of the year this


species is the important mo ,. uito of 1ryaalad. The species is highly

homophilous and is Lnown to be one of the most efficient actors of

malaria in the -~orld. The species tends to bite rmn -almost exclusivey

as has been shos.a by investigations of choice of host and preciptian

test on ingested blood. Many studies h-ve indicated that of the specimens

that were tested to determine the type of blood, more than half had

fed upon man. The adult mosquitoes not only feed on tan but select

man s habitations for resting places. They seem to prefer to rest

indoors in the darkened corners of native houses although some recent

work has shown that they also rest outdoors in secluded spots such as

termite mounds, tree holes, ete. to a far greater extent than had over

before been realized. because of this predilection for mant s habitations,

the speciess can be considered to be a domestic one. It has been shown

many times that the adults prefer to roost in native houses rather than

in European dwellings, and in any study of the mosquito densities the

ideal places to look for imnaoes is in the native villages. The adults

tend to rest on the walls or in the thatching of the roofs where it is

cool, dark, and relatively baid. It sbs shown by Badow in 1942 that

the climate within a native hut is relatively stable and that there is

a quantitative relationship between the arbers of manan inhabitants

of a hat and the mbter of mosquitoes in that bat. In general, the

ecological factors in the house, therefore, do play an important part

in the ohoite of that particular hat as a resting plaoe 1b both male

and female i squitoes. Although the female is the only form of any

importance in the transalssion of malaria, as it is the sex which

bites homans, the control of the male is equally important. Information

gathered in West Africa indicates that male mosrtuitoes are often as

naerous as are females in these native houses. The presence of the

males is another indication that the native houses provide a favored


resting place for the species. It is of zreat im-ort:ace that the

breeding '-lace, both potential --,d real, of the iAn:itutre formal be known

in any attempt to control thia :iao ulto. DeoMillon (19t7) as resinted

a rather complete description of all potrntia~l .n actual bTreediing

grounds of the iLnatures. Ho points out that "as with all other A�opnhelet

it is difficult to lay town hard and. fat rulsa about breediDn places,

firstly beoouse they are difficult to aefin- accurately anz secondly,

because in the absence of the preferred breodiaL places the species can

-ind do maker use of u t~iul waters. So far, however, there is no evidence,

either from Africa or Brazil, to dis-utc the eanoral opinion that this

F.m13os prefers to breed in emall natural collections of water completely

or partially ezposod to direct sunlight. It is a common obserwation in

South Africa that -hen the water collections are of a temporary nmturo,

such as produced by rain, they appear to be more prolifo . . .

"The types of breeding placga which come within the general definition

given above sr legion a~d r~ago from those rn rlt1eg from the activities

of man and anilsdlm such as borrow pits, drains, excavations, denuded - xd

eroded soil resulting from oeratocking, road making, deforestation,

veld burning, hoof prints, etc., thoeo resulting from overflow of rivers,

backwaters, pool left by reaeeding riwers, rainwater collected in natural

depressions, etc.

"There is a general agroeent that aumon the most iLportant of

breeding places are those created by man, for this reason breading

plaOe are often found near habitations. The-y na, of course, eoamr

in completely untiablted country (Symes, 1930, Deosillon ani oear, 1939).

DeMeillon (1936&, 1938b) found that in years of normal rainfall ambiAn

rasa largely restricted to native reserves in Natal whore overstockinl had

caused deandatio of the veld with resulting soil erosion and hence

suitable breeding places. Similarly in Northern Rhodesia the sam


author (1937a) found the ratio of adult o.bian f~ntuis is native

bats to be 0.71l near a rocent.l occupied -i2d untouched dlamo lereas

it rats 37%1 in hits or a d;abo chici hI d been occupied for some time

and was denuded of vegetation and used for -,ardenina purpose a-1d. the

digging of water holas. oss and Aylen (19" 1) have dratn attention

to the importance of soil erosion ~ndi iambI~ breeding in Southern

Rhodesia.... In this connection the observations of Rancock (1934)

during the reclrmation of the Namenve swa~p are of interest. He

found that the original swasp was innocuous but that it became suitable

for -ambia: After re almation had began. The growing of crops and the

cultivation of the soil ofton produces many breeding plces.... Apart

from turning of the soil, destruction of the vegetation, the planting

of spa4ed crope and some apecia- crops such as rice, where flooding iu

practi ad, are important nurseries (MoferP 1937, De4eillom 9l1a,

-Thob=on ISo.a aralzger 197lY.

In addition to these common breeding places, DeHeillon draws attention

to sone unsuarl breeding places such as tin oans, t-nks, cement trouwha,

gutters, tree holes, deep wells, and heavily shaded waters. All of

these are wunaal and in a normal control program uould not bo found to

be of significant importance in harborineg A, g=

Wlith regard to the rate of development of A. ~C&hta. from egg to

adult, w should like to q-ote from an earlier report (Berner, 1950).

"The rate of dewolopment for A, Xiabia has been studied in several parts

of Africa and in Brasil and highly variable results were obtained

ranging from six days to fifteen days; however, in 19W4, while I was

serving in the American arsor as entomolo st for the Interalied Malaria

Control Group at Accra (Gold Coast), I found that under exoeptionally

favorable field conditions it was possible for the species to complete

the cyclf fcLrol figg to adult in as little -;a liv) dL.ys --nadi tchit- L ix

dL'y c.icle e-i fir�' .uantly the c .ie." :Je lVe I dicu-sed the life cycle of

A. ajif in y-ra-saland with Dr. Laaborn :and it is his opinion that the1

speciess re .ulres t.,ree weeks to a month ifr this developmntal period.

iaeeillon points out Dr. Garbhg founi. that in Kiya :-.t the bedginnin

of the - pa eason and for some time thereafter the life history from

the lhitchinO , of thl egg to the adult re uired six days. The length of

time re-'uired for the completion of the life cycle is o'iouslyj of

considerable important in a consideration of control measures ndi should

be carefully determined for the spciois in iyanaland.

Data with regard to seasonal abunoanoe of . EMi in Nyasalani

are decidedly 3saroe. Mo-t of the ifi'ormatioa which we have beer. ae

to obtain regarding the seasonal occrrence of this species has been

obtained from a paper written by Dr. '. A. Lamborn in 1925. Dr. Lamborn

points out th~a in the Shire Rivpr Vallea and its im-edliato neighborhood

we have the main breeding places available fojr aosquitoes. He says that

"during the rains large numbers of temporary broodins places are formed

by the aecuisaltion of water in natur-;l And artificial hollows in the

ground most of which very oon dry up with the change of seasons. The

seasons (diacussea elsewhere in this report) in Nyasaiand fall sharply

into dry and wet{ the rains usually btogn in late Noveiabor or December

and continue to Maroh, after which there is a drought lasting until

toward the end of the year, but broken by an occasional tender storm."

Hio stud of the seasonal distribution of AnnhalPe Aa&U indicated

that it wae comparatively rare during the dry months and showed a marked

increase when the rains wore well advanced.. We are taking the liberty

of borrowing the graph show --av indicating Dr. Lambornt correlation

between rainfall in Ny&ealand and the number of & Wgft adults

whioh he collected during the years 1922-1924.



Dr. La.-,-born hi concluded that the i-itu-r of - . f i (La )

occur "in the hire- VTallae ory in the :.et season; j.mi further, t-.t

thin seasonal occurrence accounts for the ro 1t ri~e in the rnu ber of

ima;Woes thLt t.1res placq at that time." ;ith re trd to the prev~-2lon

of , 4m4inA ind the increase in the inci.enoe of maLaria, e :win

turn to Dr. LuabornIs report in Ahich he 3~ys that reliablee d.cta- as

to the part played by this anropheline (A, g~ ja---nd thi' may be:

said of all species of Anopheles in . Africa,-appear to be strikingly

meagre. If, however, gl ran (rin) is as efficient a carrier on

the east coast an has been shoen on the west, it is to bo anticipated

that its seasonal increase, occurring in the late rain, '.ll be

accompanied by the marked increase in the malris rate. So far as Orn

be ascertained, no attempt has yet been made to correl-,ta the treval~nc

of the disease i4th anopheline activity bat reports dealing 'ith the

health conditions are unanim us in emphasing, a~gin .ind again, the marLed

increase in the nzambr of cases that does take plIoe in the -wet season."

Finally, Dr. Lamborn sumarizes. his information regarding seasonal

prevalence of . rambia bVy tatiq.t thP-t "the evidence Mis been adduced

showing very definitely that the season for epideaio malaria coincides

'ith the seasonal prevalence of j, astalig (gi;ubian. 'he malarL. of

the late wet season is probably wry lrg~oy ol malaria."

Our collections during the months of SJne through Septnmber -cre

made in the season of lowest abundance of A&,. za The picture

which was reflected in these colleotiocs indicates clearly that Dr.

Lambornms findings of the seasonal incidence of this mos-.ulito are definitely

indicative of a highly restricted period of a civo Ireeding. Collections

made in native villages during early July produ cad a very low level of

adult population of this species and further collections at the end

of August showed that tha sawe still pertained, indicating that there was a

small residual population that survived the dry season in isolated habitats.

It is our belief that this residual population is sufficient to tide the species

over this period during which normal habitats are extremely scarce. As soon ao

conditions become satisfactory there is a sudden explosion of the population of

A. gambiae and very available bit of water is occupied following the peak of

the rains. The correlation, as indicated in the graph borrowed from Dr. Lamborn's

paper, shows clearly that this must be the case. Although it is difficult for

us to make any definite statement as to the distribution of A. gambiae through-

out the country based on our findings , it is obvious that the entire Shire

Valley is occupied by this species. We have collected the adults at :tundu

near Fort Johnston as well as at Port Herald at the southern end of the country.

Dr. Lamborn has listed a number of habitats in the Shire River drainage from

which the species has been recorded in the past. This clearly shows then that

there is no area within the river valley system itself that does not have to

be concerned with the control of this extremely ubiquitous vector. Xot only

must the river valley itself be considered, but those areas outside the valley

also for they represent a constant source for reinvasion should the control

program break down in any way.

Conditions along the River itself during periods of vet weather are

extremely favorable for a. gambiae. Throughout the river system there are

many pits, holes and other water-holding areas that are relatively free of

vegetation in which A. gambiae thrives. The River itself is of relatively

little importance as a breeding place as the movement of the water and the

abundance of vegetation at the banks of the river all provide conditions

which are not conducive to the well-being of A. mambiae larvae. That the river



is an extremely important factor is indicated by the fact that when the water

rises during the rainy season and then recedes, pool are left behind on the

banks and in holes in the rocks that make up part of the river bed, and in

these pools enormous hordes of the mosquito can be produced. The holes in

the rocks in the stream bed will be a rather small problem in so far as A.

Aambiae is concerned, especially since the region in which the boulders are

located is restricted to the middle stretch of the river. At the present time,

condition are extremely bad along the river banks from the headwaters of the

Shire down to point of entry into the Zambesi.

Footprints along the banks are not a serious problem in the Shire during

much of the year as they are in many other rivers. For the most part the banks

are relatively high and well drained. In the vicinity of villages, however,

there are very often shallow areas with muddy shores where footprints are

prone to hold water. It is here that the villagers visit the river to obtain

their domestic water supply. In these places, breeding of A. iambiae will

take place. Within the river itself, we noted a number of places, especially

this is true of the Lower River, where sand banks, which provide ideal conditions

for water-holding footprints, begin to appear during the falling stages.

There are also residual pools in these small sand and mud islands.

In general the situation as presented to us by the Shire River, even

during the period of low water, was that it could potentially produce tremendous

hordes of A. Rambiae during the rainy season and shortly thereafter when con-

ditions are uatisfactory. In the dry season, on the other hand, conditions are

such that there would be a relatively low incidence of this species in the

Shire Valley drainage. If the Shire Valley Project is approved and impoundment

is accomplished, the barrage that would be built in the Liwonde area would do

nothing to produce ecological changes very different from those now existing,

provided no other works not now envisioned appear.

Construction of a dam at �atope for the production of hydroelectric power,

wili, on the other hand, create a small impoundement of -ater that will drcwn

out the parts of tho rather swift section of tha river. Conditions in this area

are such now that A. Rambiae can not possibly breed in the river itself except

in pot holes in the rocks where water is left by the receding water level or

by spray. Even with impoundment, followed by the rise of water behind the dam,

conditions will still not be satisfactory for A. gambiae larvae because the

wave action in this open body of water would be to great for them to tolerate.

The slope of the land is rather steep and there are relatively few areas in

which residual water will remain, other than in the emall tributaries which

would tend to stagnate in their lower portions. It therefore appears that in

the region of impoundment their will be relatively little danger of an increase

in the prevalence of this mosquito.

In so far as the Lower River is concerned, however, the situation is

is decidedly different. Here, where the irrigation scheme is planned, the

breeding potential will be enormous. Association of irrigation projects with

epidemics of malaria has long been known and expected in tropical areas when

land improvement is undertaken. Conditions produced in various areas of

equatorial Africa following the construction of irrigation systems are almost

invariably conducive to widespread increase and stabilization of populations

of A. gimbiae. Where, prior to introduction of the irrigation systems, IaMbiae

is sharply limited seasonally, there may be a decided shift in its prevalence.

In Sierra Leone, i. Thomson (1946) investigated two areas where swamp water

rice is grown and he found that where the rice fields were cut up into small

plots aad where the water was left undisturbed for five months, either in a


continuous shot or in separate pools, larvae of A. ambiae were present during

the entire time. ihe"n, at the beginning of the dry season, the continuous

sheet of water began io dry and numerous small pools formed, breeding of A.

am3bia wIas3 sstpped u. and lasted until the water disappeared.

Although a few adult A. 2ambiae were collected in the Chiromo area during

July and larvae wore ifjnd in drying pools, we are of the opinion that during

the height of the dry season, the species, to all intents and purposes, dis-

appears from the area and does not again become important until the rains come.

If A. zambiae behaves here as it does in other parts of Africa, and we have no

reason to believe otherwise, once irrigation drains are introduced into the

Elephant Harsh region, a much greater production of this mosquito over most

of the year will follow.

Anopheles funestus Giles: This mosquito was the species that impressed

us with its abundance in the native houses. This was particularly true in the

Lower River region where we estimated that there may have been as many as 1000

adults in a single house, consisting of a main room with three small cubicules

partially cut off from it. These adult mosquitoes were not hibernating forms,

collecting in great numbers as other species of Anopheles are known to do when

they are over-wintering, but consisted of males and females, the latter far out-

numbering the former. Jales were present, however, in significant numbers in-

dicating that breeding grounds were nearby and that active breeding was going on.

A. funestus is generally regarded as the second most important malaria vector

in Africa. Numerous dissections by other workers of adult females have shown

that a considerable portion of these were infected with the malaria paratiste.

Published results have shown salivary infections ranging from as low as 0.24%

to as high as 27%. This wide variation in findings is probably of little sig-

nificance for many of them are based on few dissections. It is likely, however,


that the infection rate of this species approximates 4-Z#. This is not in-

considerable and means that of every 20-25 bites by females of this species,

transmission of malaria could possibly result. In view of the fact that the

native habitations of the villages along the Shire River, and particularly those

of the Lower River, have hundreds of adult females resting in them at one time,

the great majority of which are engorged, it is likely that the humans being

bitten each night must be constantly reinfected with the disease. A malaria

incidence of 100f can, therefore, not be surprising.

A. funestus breeds in more or less permanent water such as swamps, seepages,

stagnant parts of streams, ditches, and ether shallow waters where vegetation

is present, the water protected from wave action, and partially shaded.

DeMeillon (1947) reports that in Portugese East Africa the species breeds in

the enormous coastal flats where it is confined to swamps, ponds, marshes, rice

fields, etc.

In spite of the enormous numbers of adult A. funestus which we found in

the native houses, a careful search of nearby potential breeding places did

not always produce larvae. DeMeillon points out that other workers have had

the same difficulty in locating larvae of this species even when the adults

are numerous. In the expanse of swamps along the Shire from its origin to the

tremendous marshes in its lower reaches it is very likely that these small

larvae are so dispersed that ordinary collecting methods do not yield many. It

is well known that larvae of A. gambiae dive when a shadow falls on them and

that they can remain on the bottom for some time; however, by patiently watch-

ing a particular spot, the observer can easily catch them when they return to

the surface. In the ease of funestus larvae, the situation is somewhat different

as they are usually in protected places among vegetation. It is likely that

they also dive but when they return to the surface the presence of the vegeta-

tion makes it impossible to locate the larvae by sight. Therefore, dipping for

-3 5-

larvae is prolbu;ily sutisfictory only in very shallow seopage areas ahor'3

ood r-ot.oltc can zomatimoc bo obtained.

. fu3nost also3 sho-s a prouede.li. on for human blood and for human

uabitatioi as ros;-;n.. jla'es during nh.h day. Because of these facts and be-

cuase of tho fact that the i;pecius is numerous throughout the year in the Shire

River system, especially in tho immediate vicinity of the river, it may occupy

as i-iportant, if not a aore iipo:tanot, position as a malaria vector in Ilyasaland

than the famous A. aadbiae. The importance of this species as a malaria vector

is in oreat need of investigation.

Although A. funestus adults have been shown to have great flight capribilities,

it is lixaly that they tend to remain localized and do not wander far from

the breeding areas. Flight ranges as long as 4 1/2 miles have been found for

this specisj in Northern Rhodesia, but Deieillon working in the Transvaal

reports that the great majority of the adults remained within 1/2 mile of

their breeding grounds.

Collections of adult mosquitoes were made in villages either adjacent to

the Shire River or to the Elephant '!arch, through which the river runs.


It is clear from our investigations that malaria is a pressing medical as

well as economic problem throughout the Shire River Valley system. To ignore

this disease in the overall planning of the extensive changes to be introduced

in the country would be foolhardy. It is our opinion that careful planning of

mosquito and malaria control measures should be incorporated in the detailed

engineering plans.

The stabilization of Lake Hyasa, will hold the lake level within a three

foot annual rise and fall, with the level not falling below a certain maximum.


"We observed the shore line of the southern end of the Lake and in many places

noted that backwaters are formed behind the lake shore. Small ponds form there

and embayments of the lake are sometimes out off as the water level falls. In

the region between Fort Johnston and Monkey Bay there are also swamps that appear

to be relatively permanent. All of these swamps were characterized by being

shallow, having a great deal of submergent and emergent vegetation, and in pro-

viding conditions that are ideal for the breeding of A. funestus. Tt is ioely

that in this region suitable conditions for A. gambiae are produced during and

after the rains and also as the level of the lake falls and clear, small pools

are formed; however, the year round problem is more nearly related to A. funestus

than to A. jambiae. The lake shore itself is of no importance in so far as

mosquito breeding is concerned for the wave action is far to vigorous for these

insects to withstand the buffeting. To all intents and purposes, the actual

shore line can be ignored. The backwaters, swamps, and pools can not.

The Upper Shire, that stretch of the river extending from its exit from

Lake Myasa to Matope where the rate of flow begins to increase, has marginal

swamps along much of its length. Papyrus, reeds, and other vegetation of a

marginal type are extremely abundant in addition to floating plants consisting

mostly of Pistea, or water lettuce, and some Azola. The marginal swamps that

were in existence in this stretch of the river during our investigation, when

we saw it during its falling stage, indicate that they also are breeding grounds

for hordes of mosquitoes

As the river rises following the rains and the swamps extend laterally,

the breeding of these pests increases with the increase in available habitats.

Most of the increase of the important species in such situations is confined

to A. funestus. A. gabiae, however, will be present on the edges of these

swamps where the vegetation has not yet established itself and where there is

little or no shade. The falling river shortly after the rains would be far

more conducive to gambiae breeding then the rising stage.

The Middle Shire, that part of the river which is confined in the relatively

narrow and rocky channel extending from atope to the foot of .urchison Fall3,

is swift to turbulent. In some sections such as at ,patazanga and 'atope,

the river is torrential as it beats against the confining rocks. In this section,

the banks of the river are steep, the marginal swamps are absent and there are

few backwaters. Mosquito breeding is minimal and is confined to those small

pools left by the receding river in potholes in the boulders of the river bed

and those along the banks, and in the occasional small swamp lying behind the

river bank.

The Lower Shire is considered to be that section of the river extending

from the foot of .aurchison Falls to its junction with the Zambesi. During its

course, where it breaks up in the vast Elephant Marsh, we found the mosquito o

problem to be the most acute of any sec3is-. f the river. The shallow marshes

formed from the high water stage of the river are slow in drying because of the

high water table and the type of soil. As late as mid-August there were still

extensive wet areas that remained from the floods that occurred early in the

year. Many of these marshy areas were overgrown with vegetation and partly or

totally covered with floating plants in which conditions favorable for mosquito

breeding were produced. Although few anopheline larvae were caught, we are of

the opinion that this was not indicative of their presence for the adult catches

in the lower river were enormous. Certainly, when mosquito breeding is at its

worst, they must truly be fearsome.

The problem of steps to be taken to deal with the insects is a difficult

one to solve. Fortunately the development of the Shire Valley project is in

its early stages and mosquito control can be included in the overall plan. Two


rajor fi'ctors %;hat -muot be taken into co.nidaratior in .la)nr.in. neasures are

cost 2nd lopt:ltio'. I n an earlier section of this report, -e have discussed

)opulatuio di..*tribiutiir a.o3..g the rivar system as baoed or. the carnt information

that 'we fo'ond av I.labl. To undertake ae.tonsiva clIouring r;nasuree at the southern

end of Lake ,a.�u for eradicating breeding sitas of A. funestus would be ex-

pensive. There maany sections where the copulation is sparse and ths cos~t

of nosquito con-trol coi..id not bo justified. Were mosquito eradication to be

considered, these areas could not be neglected; however, such a desirable ond

is not yet in sight, even in the most advanced countries. It is our opinion

that in the lower part of Lake :fyasa, and this may later be extended to include

the entire Lake Shore, those marginal swa:.>,: that persist after stabilization

should be drained, if possible. Certainly some of those that were observed by

as will b3 drowned with stabilization and will, therefore, no longer offer a

problem. Such drai-age is especially important if the swamps are within two

,iles of centers :f population. The distance that control must extend from the

towns is iependent on the effective flight range of the female mosquitoes. -o

one has investigated this aspect of the biology of .. funestuz and A. ga.biad

in Iyasaland, but the nature of the terrain leads us to believe that it would

not be necessary to extend the control orofram in a radius of more than two

miles at the southern end of Lake Nyasa.

The marginal swamps of the Upper Shire offer an enormous problem from the

standpoint of mosquito control. The desirability of control of malaria and

other mosquito borne diseases must be weighed against the costs. Once stabiliza-

tion has been achieved, ths river will be maintained at a fairly high level

which means that swamps, that during the slow water stages are dry for much

of the year, will now retain their water much longer and some will become

permanent. Along a large part of tha Upper River these swamps known as dambos

vary in width from a few hundred feet to as much as two miles.

- Drainage of marginal swamps along the river would be difficult and, under

present conditions, impractical. In addition to drainage and channelizing

the permanent water, it would also be desirable to remove vegetation; however,

the removal of these plants might actually make the situations more conducive

to the wider establishment of A. =mbiae throughout the year. In view of the

fact that this part of the river is sparsely settled, except in the iort Johnston

region, it would not appear to be a feasible plan to undertake any extensive

larval mosquito control program unless there is a considerable shift in popu-

lation distribution.

The middlee River, where impoundment will introduce drastic changes in a

small stretch, does not hav3 zhe marginal swamps described above. Relatively

quiet water will, however, appear with impoundment and vegetation similar to

that of the river margin in the slower reaches will become established. Con-

ditions suitable for A. funestus throughout the year will then follow and

countless A. rambiae will also find spots in which it can survive the dry season

during which it now almost completely disappears.

Were the economic factors and population distribution different, we could

only recommend that adequate steps be taken to prepare the reservoir in such a

way that maximum mosquito control be built into it. This would entail clearance

of trees that would be drowned, keeping the margins clear of vegetation, clean

smooth edges on the shore to prevent formation of small pools and backwaters,

and other practices recommended to decrease the possibilities of mosquito larvae

surviving in the reservoir water. It is our opinion, that unless there is a

population shift to the Middle River region of Nyasaland little need be done other

than remove trees, which would intercept the surface after drowning, prior to

..* !*'

impound dmen and o-ha h steps ba akaen th:lt 'would 13ad to a rs'3Jrvoir hIat jould

be quickly and easily converted into a amoquito-froa lake. iPrevention of

establisiomnt of .marginal vegetation -Jiil be d.pensiv3 but if it is -at l3a:3t

kept in control, it will be far ar a1 or t daal with the .fobalo. if at so-me ti.

in the future, mo.sqito oontroi becomes n3cassary.

The Lower %.iver with its ih population concentrati4ns, ".vich ~ay r ecorm

even more dense after the proposed irrigation project is under way and compl-ted,

offers the aiost complex problems of the river system '.ith regards to control f

malaria. If awe assume that the huge Elephant farsh will be drained and the

water channelized, then it is likely that much of the area now inhabited by

mosquitoes will be lost to them. Theoretically, the project would improve the

situation as it now exists. Steps to be taken to make t moro than theoretical

include c n~rol of vegetation in the quiet reaches oi' the river where A. funestus

can breed, the drainage of marginal pools, keeping clean :iar3ins along the river

banks so that water holding footprints do not appear, and providing sanitary

facilities for drinking water as aell as for sewage disposal.

Russell (1946) points out that "irrigation works have been a source of

malaria in many countries. No one has any quarrel with irrigation, in fact,

properly controlled, such works will do much to raise the economic status of a

people. In many areas the very life of a community depends on irrigation.

But it seems fair to ask why engineers are given budgets to bring great quantities

of water into a region but at the same time are not provided with funds to re-

move this water by counter-drainage. naturally, in the absence of drainage,

ground-water levels rise and malaria frequently increases....

"It should be stressed that, for the most part, it is not irrigation itself

which gives rise to malaria, but it is defective and untidy irrigation which,

by misplacing water, allies itself with malaria-carrying anophelines, multiplying


their breeding places...."

The mosquito breeding areas that will be produced by irrigation may be

in both the channels and in the overflow from these channels wherever water

stands for a few days. Conditions that may be created will favor both important

species of anophelines, A. gambiae and A. funestus, as well as several others

which are of no particular importance as vectors. Abundant evidence in the

literature points up the fact that very profilic breeding of dangerous anophe-

lines follows harvesting of crops when water stands in the fields undisturbed,

or in the swamps created by the run-off from irrigated fields.

It is well known that an increase in water surface, especially that of

shallow water, provides an increased opportunity for mosquito breeding. As

A. funestus is associated with vegetation or debris floating in water, the

intersection of the surface by these materials grossly increases the available

habitats for this species. In the case of A. ~ambiae, which prefers open pools,

the multitude of small depressions in drying fields, left after irrigation,

provides adequate habitats for the larvae, which in general, prefer edges of

these pools. Therefore, an increase in marginal area (the water's edge)

definitely favors production of this mosquito.

It was pointed out above that Muirhead-Thomson (19.5) studied flooded

rice fields and mosquito production in Sierra Leone. There he found that at

the beginning of the dry season, when the continuous sheet of water over the

fields begins to shrink into numerous small pools the breeding of A. gambiae

increases considerably and production of adults continues until the area is

completely dry.

In Kenya, Grainger (1947) reported that a rice field near Kisumu was under

irrigation. There, A. gambiae was a persistent breeder with an average production

varying between 0.1 and 3.3 mosquitoes per 12 square feet of paddy field per


Thus these two instances of using irrigation in widely separated part of

equatorial Africa show that regardless of the area A. gambie is able to

quickly accept these newly created habitats and to flourish in them. There are

other areas in this huge geographical unit, all inhabited by 1. gambiae, that

duplicate the picture with regard to irrigation and increased production of

the mosquito.

Experience in India in dealing with similar malaria vectors and irrigation

has led investigators to summarize the problems that are created by perennial

irrigation. These are as follows:

1. Increased height of subsoil water and the greater tendency of the

water-logged soil to form long-standing pools during the rains. These

pools and puddles are very extensive in fallow fields close to the

main channels.

2. Prolific breeding in canals when they are temporarily shut off either

for repairs or for periodical distribution of water. These canals

when reopened carry anopheline larvae into the subsidiary channels.

3. Along the high level canals there are strings of water-filled borrow-


4. Breaches in canals due to natural causes or illicit removal of water

produce numerous breeding places.

5. Bad maintenance and subsequent leakages from small channels under the

control of local populations.

6. Obstructions of old canals or streams by roads or new canals which

form land-locked depressions.

7. Insufficient number of bridge crossings and subsequent damage to

the banks by traffic.

8. Rise of subsoil water level caused rise of water level in deep wells

with the result that conditions are now created favoring anopheline

breeding. Also, it makes it easy to dig shallow wells during dry

season, again producing new breeding places.

9. Excessive supply of water which overflows and gives rise to pool0013

along sides of the canal.

10. Defective sluice gates and distributing chambers.

Ghwatt (1950) points out that it is the unspectacular and commonplace

peripheral part of irrigation schemes that are usually neglected producing

numerous seepages, leakages, pools and puddles in which breeding of anophelines

is prolific. He emphasizes the important point that large areas of water are

less dangerous than small pools since the amount of anopheline breeding in

tropical Africa is proportional, not to the area of water surface, but to the

length of the water edge.

The above discussion of conditions along the Shire River with regard to

the anopheline problem as it now exists and the potential hazards that will be

created by the engineering changes indicates in reality there will be little

or no modification in malaria prevalence. Vector mosquitoes are common through-

out the year, although there is some evidence indicating that malaria trans-

missionain thezriver system is predominant during and following the rains. Per-

haps stabilization of mosquito production throughout the year will result in

an even higher transmission rate, but until something more definite is known of

the malaria incidence in the country this will have to remain as a bare supposition.

Since our conclusions indicate that the malaria situation as it now exists

will not be materially affected by changes in the river system, is it worth


while to consider steps to take in freeing this region of Africa from the

scourges of the disease. In our opinion it is; however, the problem is not

only an entomological and medical one, but, probably more important, a

sociological one and all aspects of this factor should be investigated. Perhaps

if is the most important of all for are we not defeating our purpose if we

free people of a killing disease only to permit an increased po-,plation which

is unable to feed itself, and must, therefore, be subjected to famine? As this

report deals with the insect vectors we shall not presume to judge the problem

from this sociological standpoint.


We recommend that the following steps be taken to control malaria and

malaria mosquitoes in the Shire Valleys

A. As soon as feasible appoint an epidemiologist especially trained in

the field of malariology. He should undertake an intensive investigation of

the malaria incidence in the country, its distribution, and the species present.

As additional problems may be created by the importation of labor forces to

construct the dam, barrage, and irrigation system, he should also investigate

the implications of mass idigrations of the native peoples. An added function

would be the regulation of the location of both European and native housing

with the malaria problem in mind.

The malariologist should maintain close liaison with the engineers to

insure that maximum cognizance is paid to conditions favoring mosquito production

and that they are built out of the scheme

B. Many new malaria prophylactics are being being produced and investigated

today. It may be possible to make great advances in the control of the disease

by the distribution and use of these drugs among the population. The malari-

ologist should investigate the potentialities of this type of malaria control,

and, if deemed feasible, should undertake the procurement and distribution

of the drugs. Handling of drugs in a country where the educational level is

low is subject to much abuse. Great care should be exercised in setting up a

system to distribute the drugs on an equitable basis.

C. It would be highly desirable to engage the services of an engineer

specially trained in mosquito control engineering to serve as A consultant

during the construction phase of the Shire Valley Project. The engineer would

advise on details of planning to insure the greatest possible use of construction

details to control mosquitoes. Often such a aan, trained to see hazards, can

save great sums in future mosquito control projects.

D. It is essential to have a competent entomologist on the job full time;

especially during construction and for the first two or three years after

completion of the project. Identification of mosquitoes, their breeding cycles,

biting habits, flight range, knowledge of other aspects of the biology of the

insects in Nyasaland are sorely needed. A well conceived and carefully planned

mosquito control project must have a firm scientific basis to insure 'aaximum

effect at the lowest possible cost.

E. Modern, good equipment to control the insects is essential. To pur-

chase inferior equipment for a long time project such as this would be a waste

of money. There will be needed for laboratory equipment, boats, vehicles,

sprayers, both power and hand, as well as many smaller items. If at all

possible, there should be no stinting on these articles.

r, Control steps

1. Wherever possible the marginal svwaps and marshes should be drained,

or, if this cannot be done, water should be channelised to make larval control

more successful.

2. In regions of relatively high .op,.lation density, and where it is

can be accomplished, control of mosquitoes by larval destruction 3h'uld be in-

stituted. In the Lake lyasa and 'pper and Middle River sections, control within

a radius of two miles of the area to be protected should be satisfactory; how-

ever, the control radius must be studied carefully as the cost factor will bo

important here, This point can only be sot'led b. a study of the effective

flight range of both A. gabiae and A. funestus.

3. All borrow pits should be dug in such a way that drainage is rapid and


4. The impoundment area behind the dam should first be cleared of all trees

that might project above the water surface after formation of the new lake.

Initial removal of marginal vegetation could be accomplished at the same time,

as well as cleaning of banks and shaping them for the rapid removal of surface

water without subjecting the land to erosion. This will prepare the basin for

future mosquito control should the population in the region increase.

5, In the Lower Piver where population concentrations are high, it will

be desirable to undertake larval control within a radius of at least two .iless

however, the radius may have to be increased if it is later found that the

anophlines are able to migrate longer distances than this,

a. Marginal vegetation should be removed from the river.

b. Pools should be drained.

c. Definite watering sites should be provided for Africans requiring

larger quantities of water than can be provided by sanitary wells.

These should be kept free of standing water.

6. a. When the irrigation system is built there should be careful plan-

ning of water distribution and efficient supervision of it after

irrigation has started.



b. Staps, should be taken to avoid those situations (discussed above&

which might l-ad to the production of dangerous broadinz grounds.

c. 4ide legal powers should be granted to the authorities to ;ernait

them to enforce a proper maintenance of the irrigation channel

by the farmers.

7. Sanitary drinking and washing facilities should be provided for all

villages or concentrations of peopi2. The wells should be properly enclosed

and built ao that refuse does not run back into them. There should be no

standing water around them.

8. Jatives, who have to be resettled because of inundation of their lands

or to develop newly opened lands, should have their houses built in safe areas.

Adequate, completely sanitary drinking water should be supplied for them. ?its

dug for materials for house construction are common in Iyasaland; these should

not be permitted to be left unfilled as they provide mosquito breeding sites.

9. The never insecticides such as D. D. T., gammexane, and others have

proved to be extremely valuable in the control of mosquitoes. Recent information

indicates that they will have to be used with care and that their use may not

be a final answer to mosquito control. Studies in the United States, Korea,

and other parts of the world have shown that insects develop a resistance to

these insecticides and after a while they become ineffective. Nevertheless,

we strongly urge that a carefully planned and executed program of spraying of

native houses be conducted to control A. gambiae and A. funestus, two species

which are particularly susceptible to this type of control. The spraying must

not be haphazard and the intervals between spraying must be spaced so that at

no time is the amount of residual insecticide within a house insufficient to

kill adult mosquitoes. This method, appears to offer the cheapest, quickest,

and most satisfactory method for the control of mosquitoes in regions such as


Nyasaland. The entire program should be under the careful s..parvisiro of Well-

trained personnel and should never be entrusted to others. If the spray pro-

gram is half-hearted the amount of control will be neglibible.

10. The ideal would be to attack the mosquitoes by all means availublo.

This would include not only recommendation number 9 but also larviciding on a

regularly scheduled basis. Until the life cycle of the anophelines concerned

has been determined accurately, we recommend weekly larviciding of breeding


11. One of the best larval controls in irrigated land is intermittent

irrigation wherever possible. The number of wet to dry days will depend on

the breeding cycle of A. gambiae and A. funestus. Since Grainger (1937) found

in Kenya that 3 dry to 7 wet days did not materially reduce the number of A.

da.biae, the method may not be applicable to equatorial Africa. ie recommend

however, that a careful study of this method be undertaken in the Lower River.


Filariasis has been reported from 3yasaland, but only in recent years.

The "Annual Report of the Medical Departient" records the disease for the

first time in the l~:. i-sue by pointing out that at -aronja 30 of' tho

patients show microfilaria of ',juchereria bancrofti,. Th report india~-os

that only two of the patients showed clinical 3i3n., b'.t Cea3e of ol3:)hant.iiasis

occur each year on the lake shore and in the Lower Shire River.

Wile we were collecting mosquitoes from villages in the Lower River region,

we were struck by the number of people who showed signs of elepha-itiasis.

Whether this elephantiasis was due to the filarial worm has not been deter-

mined. In Port Herald, we saw several people that were showing obvious isyrptoms

that miizht be attributable to the disease. The fact that thoa condition is so

noticeable in this section -f the country clearly oi:.ts up the need for

parasitological examination of these people.

It is difficult to assess the need for work in the field without a more

clearly established epidemiological picture; however, circumstances load :.3

to believe that filariasis should be considered as one of the problems in the

overall betterment of the health conditions of 'lyasaland. As enlarged body

parts are associated with the presence of the worm in five percent or less of

those infected, a gross examination of the population would show little in

so far as establishing the prevalence of the disease.

The transmission of filariasis has been demonstrated through the agency of

various species of mosquitoes of whieh the following occur or are widespread in

Nyasalands Anopheles gambiae, A. funetus, and A. nili. Both Taeniorhvnchus

africanus and T. unifornis are very common over much of the Shire River but it

has not been established oonolusively that they can transmit the disease,


although development of the worm has been observed in them in Contral Africa

(Manson Bahr, 1945). Other species that have been incriminated as potential

vectors and which occur in iyasaland are Culex fatigans and Aedee 3._1ti.

Various workers have studied mosquitoes in Africa in an attempt to correlate

mosquito species with transmission of filariasis. Gordon, in 1932, dissected

22 female A. nili taken near Freetown and found 4.5, of thoa: with i.ci.,ient

infections in their thorax. Barber working in Nigeria dissected 254 femal3s

of the same species and found 2.7, with filaria. 3vnns (1933) says that heree

A, funestus occurs, it must be an important vector and she lists six references

to workers who have found infected sy~, .;ens. Agreement is rather general,

however, that A. gambiae is probably the most important carrier of W. bancrofti.

Infections of this special have been reported by many worker.

The effects of the engineering changes on A*. ambiaa and .A funestus

have beoon discussed in the section on malaria. Should steps be taken to doal

with these mosquitoes, they will also react favorably on the incidence on

filariasis should those mosquitoes be proved to be the chiof vectors of the

disease. Nevertheless, the importance of T. africanus and T. uniformis cannot

be discounted without a thorough investigation of their relationship to the


Both of the species of Taeniorhvnchus are associated with vegetation,

particularly with the floating plants, Pistea and Atola where we found them in

great abundance in the Upper and Lower River, The rapidity of the flow in the

Middle River discouraged the establishment of plants favored by these two

mosquitoes, known locally as grass mosquitoes. The larvae and pupae attach

themselves to the roots of the floating plants and do not normally come to the

water surface to respire as do other species of mosquitoes. Adults are vicious

biters and attack in the open mostly during the daytime both in sunlight and

shade. - They are particularly numerous during the low water staje of the rIver

when the floating plants have an opportunity of becoming well established .

They are also ncumerous in residual swamps loft by the rstreatinr water follow-

ing flooding of the river.

Control of Taeniorhynchus is a difficult problem as house spraying, so

effective against certain of the African anopholines, will not work with these

species. Removal of water lettuce and Azola would be a costly and laborious

procedure, but it could be accomplished should the prevalence of filariasis

make it necessary to undertake control of these mosquitoes. The costliness

of this control makes it mandatory that the need for it be clearly established

by both epidemiological and entomological studies.

Se, therefore, recommend that prior to the inception of any control steps

the epidemiologist and the entomologist uLdertake a study of the human host

as well as the vectors, and that if, in their opinion, conditions warrant con-

trol, then it be instituted along with malaria control.


The blindness caused by the filarial worm, Onchocerca volvulus, has been

recognized in recent years to be of far greater importance than had over been

realized. Wide interest has therefore been created in the distribution of the

disease and its epidemiology. During the investigation of the Volta River

disease vectors (Berner, 1950), it was shown that the onchocerciasis is extreme-

ly widespread along the river system and is of major importance as a factor in

depopulation. The vector of the worm in lest Africa has been proved to be

Simulium damnosuq, the black fly.

Although the disease has been found to be prevalent in various countries

of East Africa, it is scarcely known from iyaealand. a. L. Gopsill (1939) has

reported twenty cases , all from the Cholo district where the disease if said

to be related to the presence of the mountain streams and the proximity of the

tea plantations. Other than these cases we have been able to find no evidence

of the recognition of onchocerciasis in the country. After talking with various

medical officers, we were left with the impression that the disease .:ay be far

more prevalent than is indicated by the record. It simply has not been recog-

nized nor investigated.

Onchocerciasis is widely distributed throughout Central America and

Southern Mexico and is associated with swift mountain streams in which the larvae

of the vectors live. It is also present throughout most of Central Africa

where it is also associated with swift streams which provide th: habitats for

the black fly larvae. Man appears to be the only host for the worm, though it

has been suggested that other animals may possibly serve as reservoirs. Micro-

filariae are present in the skin of an infected person and when he is bitten


by a black fly they pass into its body. Here, the worm develops during a

period of from six to ten days or more. Infection of M6., takes place through

contamination of the bite.

Even though the disease is not recognized as being of any importance in

Nyasaland, we felt that the potential dangers inherent in the presence of the

vectors warranted our spending some time in I-nvestigating the species of

Sipmlium present and their distribution in the country. As the male Nyasalander

appears to be addicted to wandering over Africa and then returning to his

native village, the likelihood of introducing the disease into areas free of

it are rather great, especially now that travel has been made so easy.


Although we made a careful search for crabs and insects on which the

larvae of Simulium nevi, and important East African vector, live, no specimens

were taken that could be positively identified by Dr. Paul Freeman as of this

species. Nevertheless the likelihood of the species occurring in Nyasaland is

considerable. On the other hand, Simulium damnosum was found in many places.

The larva of S. neavci was only discovered in 1950 by 1kacuahon in Kenya

where it is associated with crabs and mayfly nymphs. The insects attach to the

bodies of the orabs where they are protected, yet in a favorable position for

obtaining food and for respiration. The crabs in Nyasaland appear to live in

the swifter mountain streams where they hide under stones and in other protected


iM lium damnosum larvae require swiftly flowing water, which appears to

be the major limiting factor in its distribution. The pupa occurs in the same

location as the larvae, even when the water is torrential. One of us (Berner,

1950) has discussed the biology of the species at some length and the following

is quoted from the report:

"the chief factor which appears to influence the distribution of

the fly is the rate of flow in streams. Wanson and Henred (1945) found

that in the Congo a current of 3.3 - 1.3 kilometers per hour was the

most suitable rate for the development of larvae. Ao larvae were found

when the water flowed faster than 3 kilometers per hour and the mii.imum

rate was found to be 3 kilometers per hour....

"Whether Wanson's and Henred's conclusions are valid is now open to

question. Since their results were published, Lewis (1948) has found

larvae of _, damnosau breeding on hard mud in comparatively placid stretches

of the Aile in the Anglo-Egyptian Sudan. His larvae were taken from water

flowing at a rate of about 2 kilometers per hour. It is very possible

that in West Africa this mud-dwelling habit is developed by the larvae

but has not yet been discovered by entomologists investigating the insects.

"...Briefly, they (Wanson and Henred) have found that the eg&s,

which are glued by the ovipositing female to some underwater objects in

swiftly flowing water, hatch in a few hours. The newly hatched larvae

attach themselves to aquatic plants, detached leaves, sticks, or rocks

which are firmly anchored in rapid water. The larval stage lasts five

days, when pupation occurs in the same type of habitat in which the larva

develops. The pupal stage takes four days, about nine days being required

in all for the complete egg - adult cycle. The duration of the larval

stages in the Congo appear to be constant regardless of the season as

there is little variation in the temperature of the water of the rapids,

where it ranges from 23.50 - 240 C, Eggs are not matured in the female

until after a blood meal is taken, but if the meal is adequate and the

external temperature high enough, the eggs will develop in 3 or 4 days.

About 200-250 ova are laid at a time.

"Probably the controlling factor in the speed of the current is

the amount of dissolved oxygen in the water. There the streams is tur-

bulent, the water becomes thoroughly mixed with air and saturated with

oxygen.... Food is obtained by the larva from the flowing water by strain-

ing out the plankton with its two, long oral fans which it holds out-

stretched against the current....

"After completing its pupal development, the insect emerges as an

adult during the early hours after daybreak. Soon after emergence, there

is a concentration of the new adults on the vegetation in the vicinity of

the rapids. In the Congo, the males concentrate around flowers of the

leguminous tree, Baphia bossenge, on which they feed, or on the under sur-

faces of the leaves to rest. The females search for a host from which ta

obtain a blood meal. Mating probably takes place after the maturing of

the ova. Longevity of the adults has not yet been determined.

"The maximum distance which the female S. damnosum can fly has never

been demonstrated, but circumstantial evidence has led some observers to

credit the species with remarkable powers of flight. Gibbins in 1936

reported that swarms of adults were found at Kampala, Uganda, and that

they had flown from the Nile, a distance of 72 kilometers. He considered

that streams near Kampala were not suitable for breeding of the species.

Wanson et al (1949) estimated that the insect was migrating 40-45 kilometers,

and in 1945 captured adults 15-20 kilometers away from breeding places.

Lewis (1948) reports that at Handab, Anglo-Egyptian Sudan, several


kilometers from a large breeding area, biting adults were common in the


"The effectiveness of the ability of Simulium to transmit oncho-

cerciasis has been proved in Central America as well ao in Africa. The

infected flies form a rather large percentage of the populations, and

even those which show infective larvae are common. Considering the great

number of bites sustained by people in a Simulium area, an infectivity

rate of 1% is far more than sufficient to insure infection with the dis-

ease. Wanson et al (1949) reports that 2.9% of the female S. damnosum

taken in villages on the banks of the rapids of the Congo, on dissection,

were found to have infectious larvae in the head. 13.3l~ of the adults

dissected had incipient infections in the muscles of the thoras. It is

hardly surprising, then, that every human living in such villages shows

infections of the wora as they are bitten by the flies countless times

each year resulting in repeated re-infections."

A number of attempts to capture adult Simuliun along banks of streams in

Nyasaland resulted in the collection of only six adults. Both of us as well as

natives served as bait; however, the population of the flies was small, as

indicated by the larval and pupal collections, and we were not attacked. It

is highly probable that during the rainy season when the flow of the streams

increases that there is an enormous increase in the populations of this insect.

The need for additional study of this entire problem is clearly evident.

While the investigation of S. damnosum in the Gold Coast (Berner, 1950)

was under way, larvae of this species were never found in the smaller streams

and it was suggested that the rate of flow was the limiting factor. In

Nyasaland, on the other hand, larvae of damnosum were collected from, several


small streams but only in those places where the current was swift. The

collections of Simuliua are given in detail below:

13.5 miles east of Fort Johnsons Simuliurc niaritarsis, S. medusaeior-e

Nkazi stream 3 _. adersi, S. ruficorne

Lingmazi stream n _. in-.ukane

11 miles north of Aamwere 3 S. alcocki

Namwere ; . unicornutum S, n.igritarsis,

S. alcocki

3 miles South of Gandi : S. amqhoni, S. adersi

Tengadzi stream S . mcmahoni, S. darnosum, S. vorax

19 miles north of Chiromo : S. momahoni

Mwanza stream 3 S. damnosum, S3 vovis, S. adersi

Matope 3 S. damnosum

Liwonde : a. griseicolle

Walker's Ferry : . adersi, S, - cmahoni

Mpatamanga : _. adersi, a. damnosum,

-. mcmahoni, S. griseicolle

Limbe 3 '. alcocki

10 miles east of Limbe : �. medusaeforme for. hargreavest

11 miles east of Limbo a B. unicornutum form rotundum,

S. nizritarsia

9 m.les east of Cholo I S. damnosum

Likabula stream Ia . deqtulosum, q. orax

3 miles west of Ulanje 2 . unioornutum, S. cervicornutum

Zomba plateau s -. alcocki, _. hirsutum,

A. nixritarsis, A. tentaculum,

o. vorax, -. debegene, .S dentulosum,

S. tentaeulunm, . taylori

In a personal discussion of the Simulium species with Dr. Freeman of the

British Museum, we were told that it was his opinion that S. neavei, the

other vector of onchocersiasis occurs in :yasaland, in spite of the fact that

we were unable to collect specimens.

From the above listed records of collections, it can be seen that .,

da.nosum, even during the dry season in Nyasaland, can be found in the sMailer

streams such as the Tengadzi, the zwanza, and others as well as in the parent

river, the Shire. That the species was not abundant enough to be noticeable

during late June, July and August, is not surprising as the same behavior was

noted in the species in West Africa when the Volta River was at its low stage.

It is our opinion that a few individuals are able to persist in the moat

rapidly flowing parts of the streams until conditions are propitious for a

quick expansion of the populations.

The vector species were not taken in the Upper River where the flow is

slower; however, the presence of S. griseicolle at Liaonde leads us to believe

that during high water ., damnosum might also be in this part of the river,

but probably no farther north except in some of the more rapid tributaries

which flow swiftly for a few weeks or longer. Conditions in the higher streams

of the Namwere hills are satisfactory for crabs and indications are that the

larvae of g. neavei are associated with them. ei found young larvae of Simulium

attached to crabs from these streams, but they were too small for specific

identification. Additional collections are required to, establish definitely

the name of the species associated with the crabs.


The disease, onchocerciasis, has been reported from Nyasaland. We have

established the fact that the vector insect is widely distributed throughout

the river system. The medical department knows practically nothing of the

epidemiology of the disease in the country nor has any case of blindness in

the country been attributed to the presence of the worm. The question

naturally arises as to whether the disease need be considered at all in the

overall protection of the population. We hold that it does, not because of

the present situation, but because of the potential danger of spread of the

disease. We have indicated the hih degree of infectivity that is associated

with the vecotr species. Jith the widespread presence of the insect, it would

take only a few human carriers to soon disseminate the disease widely through

the country as has happened in Central America and southern Mexico.

Newer methods of control of these insects are being developed with

great promise os success. In the smaller streams in Kenya where onchocer-

ciasis is present, Garnhaj and Mc.1ahon (1946) have demonstrated that Simulium

neavei can be completely eradicated by the use of a simple technique. Large

rivers pose another problem, but Wanson, Curtois, and Lebied (1949) showed that

S. dainosum could be eradicated from the Congo in the Leopoldville region by

an attack on the adults.

A consideration of the Shire Valley project and its effects on the pre-

sence or absence of the Nyasaland species of Simulium indicates that there

will be little change in the conditions now existing. After construction of

the dam in the -Middle River, the region impounded will be sufficiently static

so that larvae of S. damnoeum cannot inhabit it. As S. neavei does not appear

to live in the larger streams, it will offer no problem. Other than in that

one section, S. damnosum can persist in the Shire wherever the rate of flow

is sufficiently rapid.

The smaller tributaries of the Shire will not be materially affected by

impoundment and irrigation; therefore, production of the vector species can

continue unabated unless it is decided to attempt eradication.

In our opinion, there should be an epidemiological survey to establish


the presence or absence of the disease. If it is discovered that there are

no longer infected individuals living in the country, then the problem is

obviously only a potential threat. If, on the other hand, only a few in-

dividuals are found to hzve the disease and these persons are localized,

then control can be carried out on a limited basis. To eradicate the insect

vector from the hire would be fairly expensive, and it would be highly

desirable to know all the factors involved in such an undertaking.

Control of vectors in the smaller streams using the technique of the

Kenya workers would, however, be relatively easy and inexpensive. The

method simply involves the dripping of a D.D.T. eanulsion into the stream

in the regions above the breeding areas of the vector species. Garnham

and McMahon demonstrated complete eradication of these vectors. Whether

or not eradication would be permanent would depend on factors other than

eradication from the single stream treated. It was pointed out above that

2. damnosum has extremely great powers of flight and might, therefore, re-

populate a stream from which it had earlier been eradicated by wandering in

from neighboring streams in which no control was undertaken, It would,

therefore, be essential to closely observe streams that might serve to re-

populate the one's whe. under control. This same technique could be applied

to the irrigation drains should the water flow at a sufficiently rapid rate

to permit the establishment of 5. damnosue or S. neavei.

The Shire River may be too large a stream to make the use of drip cans

practical however, as habitations along the river in the vicinity of rapids

is now very limited, there may really be no problem in so far as the disease

is concerned. Nevertheless, the drip can technique might be tried, at least

on a limited sale, if control or eradication of S. damnosum is undertaken.

Drip cans can be suspended from the bridges at a&tope and at Mpatamangas


It would also be relatively simple to rig up arrangements for dripping D.D.T.

emulsion at other points on the river where S. damnosuv occurs by stretching

cables across and suspending drip cans from them.

It if is shown that th. drip can technique will not work in the main

river, the far more expensive method of the Belgian Congo workers might be

considered. This involves aerial spraying to kill adults. These workers at

first attempted to use larvicideo to destroy the insects but in a river the

size of the Congo, enormous quantities of the material were required and it

was seen that it be impractical to utilize this method. "Consequently, they

decided to attack the adult stage. Preliminary tests indicated that D.D.T.

was an ideal insecticide to use. After experimenting with various methods of

applying the material, it was found that spreading it in the form of an aerosol

by aeroplane was the most effective by far. A very careful preliminary study

of the area was made, and the density of the adult Simulium population was

determined. The spraying was then begun on the theoretical assumption that

eight fumigations in two weeks would destroy all adults which were 'on the wing'

or which might emerge from the river. Since no additional eggs would be laid,

the species would be axtorminated.

"Actually, it was not so simple. More frequent flights were necessary

at first. Later, it was discovered that the area in which eradication was

desired was being reinfected from a reservoir population that had been over-

looked. On 10th October, 1948, using a single airplane, flights were made

every other day over the area and the work was continued for 26 days. Their

results were sensational. Within the first two days Leopoldvilie was practi-

cally freed of the insects. On the fourth day small native villages within

the 45 kilometer perimeter were completely cleared. By the end of three weeks

of spraying, larval habitats were deserted, indicating a cessation of oviposition.

One year later, Leopoldville ~wa still. free of Simulium. There still remained

the danger of reinfestation of the region from rapids here the flies were un-

controled. By establishing barrier zones beyond the greatest possible f liht

range of the adult femala2s, they have inesred against reestablishnlent of the

fly .n the rapids at Leopoldvile." (Bernor, 1;0).

The relatively limited sections of the shire which are inhabited by S.

damnosum moan that control by aerial spraying would be relatively easy as it

involves only that section between Liwonde and the foot of Murchison Falls -

the Siddle River. However, such control would be uselees unless it were

correlated with control of the insects in the smaller tributaries, which could

be a source of reinfestation were they not also considered as a part of the

whole scheme.

We believe, then, that the epidemiological study should be undertaken at

an early date. Should the disease be considered by the epidemiologist as

being in need of control, then an entomologist would be required to make a de-

tailed survey to determine the distribution of the insect vectors in the waters

of 'Iyasaland. It would be necessary to know a good deal about the biology the

species, including the length of time necessary for development, its seasonal

prevalence, flight range, and other pertinent aspects. The entomologist would

also supervise eradication and would continually check to determine the effects

of his program.

Human sleeping sickness, the scourge of equatorial Africa, is present

but not widespread in 'yasaland. During our brief stay in the country, a suall

outbreak of the disease was discovered in the western part of the CGhikwaw-

district and we were informed that there were a few cases in the Kota Kota

region. In general the disease appears to be very localized.

Recognizing the tremendous danger inherent in the presence of the vector,

Olossica morsitans, the government of Nyaaaland has set up a division of

Tsetse and Game Control to deal with the problem. Shortage of funds has

necessarily impaired the program; however, studies of the distribution of

the insects and their relation to the vegetational associations, so important

in the control of tsetee, are now under way.

Because of the work being carried out by this governmental agency, we

gave little attention to collecting tsetse flies. We did discuss the problem

at some length with various representatives of the medical department and with

Ur. B. L. titchell, entomologist for the Tsetse and Game Control Department.

Mr. litchell very kindly provided us with a map showing the distribution of

tsetse in Nyasaland. This is reproduced as Uap 2.

In our opinion, the Shire Valley Project will have little influence on

the presence or abundance of G0losina morgstana. Ecological changes which

will be produced do not impinge broadly on the territory inhabited by the fly

and we believe that the changes will not bring about much, if any, change in

the present distribution of 0. morEitans. It is more likely that 0. brevipalpis,

also known from Hyasaland, and which has an extremely localized distribution,

might become more widespread, but this must be pure speculation.

Our discussions with Mr. Mitchell clearly indicated to us that he was

fully cognizant of the problems inherent in the presence of an efficient vector

and carriers of a dangerous disease. He is very much aware of techniques ol'

tsetse control being used elsewhere. Apparently the major factor hinder-ns

control staps is financial.

That preventive rather than firo-fighting techniques are required is

evident. It is frustrating to be forced to wait until an outbreak of a danger-

ous disease occurs before it can be fought, when the tools and techniques for

stopping the outbreak before it ever starts are available. We feel if it is

at all possible that considerable support be given to the tsetse control work-

ers, both in personnel and finances, so that they may eradicate trypanosomiasis

from Nyasaland.

A major factor that must receive considerable attention in controlling

the disease is the migration of natives from the Portugeee territory into

Nyasaland. It was indicated to us that many of the cases originated in ?ortugese

East Africa where there is little or no effort to control Glassi a. Any con-

trol program would suffer by a continued import of sources of infection ana

this is precisely what is happening in this relatively unrestricted immigration.



Although schistosomiasis is not an entomological problem we were asked

to Include the Il3iao in our i.-vestigation. Nherefore, whenever collections

of mosquito or other aquatic insect larvae rere zade, snaila w-re alao col-

lected. At the time of writin~ this report, the spocriena have not arrived

in the United States and are consequently unidentified. 's therefore plan to

submit a supplementary list of species of snails and the places from whIch they

were collected.

There is a great deal of interest in bilharzia in Nyasaland for both the

medical officer and the layman realize the great drain of this disease on the

native population. Within recent years, as more and more Africans attend dis-

pensaries and ho-pitals their attendance is reflected in the increased number

of cases of schistosomiasis recorded from the country.

A study of the annual medical reports leaves a feeling of vagueness with

reference to the prevalence of the disease prior to 1944 when the number of

cases observed are reported. In that year 4,752 cases -ore seen. The 194- re-

port listed 3951 cases of urinary bilharzia and 740 of the intestinal form.

By 1948 the number of cases amounted to 7560, and in 1950 16,635 persons were

reported infected, along with two deaths attributable to the disease. The

1950 report points out that although the disease is not a killing one, it has

a tremendous influence on the standards of education and the level of productivity

of the adult population.

This same 1950 report discusses the situation in Nyasaland showing that

92.12% of the Kota Kota school children and 40-50' of the adults showed an

infection with S. haemotobium. In the Domira District there was an overall

infection rate of about 0;. From 1925-1939 the cases which waer diagnosed at

the central laboratory showed 13.4" to b.- S. mansoni and in 1950 11.9, of

those in hospital were infected. The distribution of . mansoni ranged from

none at zalaiba in the northernn Province 1lighlands to 27.7i at xaronga.

Dr . D . Di.air (1752) very briefly summarized the situation with regard

to bilharzia in ;':ysaland in a report for the worldd iHalth Organization; how-

ever, his report did not particularly clarify the picture since he did no addition-

al survey work in the country.

Faust (1949) discusses the geographic distribution of S. haemotobium and

lists Ayasaland as havi-ng 30~ of the population infected. According to this

author 20-303 of the population is infected with S. =ansoni, but he fails to

give the source of his information relative to percent of infections.

Discussions ith various members of the medical cepartmenrt indicate that

the alsease is certainly pidaspread and that, perhaps if repeated examinations

of the same individuals could be carried out in a survey, rather than a single

examination, 100, of the children of school age would show infections with S.

haematobium in the villages along the Shire River. Dr. 7. A. Lamborn is of the

opinion that the three most important diseases in Nyasaland are hookworm,

bilharzia, and malaria. There is some disagreement among the Hyasaland doctors

as to order of importance of the three, but there is general agreement that

all are extremely important to the people of Nyasaland.

In areas where the disease occurs, promiscuous urination or defecation by

infected persons provides the means for infection of appropriate species of

snails. Once the excreta, bearing eggs of the worm reach water, they hatch and

laberate the free-swimming miraci4ia. This larval stage then penetrates the

snail in which it undergoes a metamorphosis to form primary and secondary

sporocysts and cercariae. The ceroariae leave the snail ard, if successful,

-'J -

penetrate the skin of :an, beginning a new infection.

Infection with S. hae-:otobiun is acquired through contact with water in

which the infective cercariae are present. In EBypt, ~where infections are

widespread, the disease has tended to increase as the irrigation projects from

the Nile have been extended into previously arid districts. The distribution

of the snails is such as ta cause the corcariae to be present not only in the

irrigation ditches of the fields but also in the larger canals passing through

the villages. Farm laborers in the field, women washing in the canals and the

children playing and bathing in the larger bodies of water are constantly ex-

posed to infection, while cercarie taken into the mouth with untreated drinking

water constitute an additional hazard.

Faust (1949) points out that "The vicious cycle is increased the more by

the observance of certain religious practices. The *ohammedan religion pre-

scribes that the urethral and anal openings be washed with water after urination

or defecation. lale villagers therefore seek the bank of the nearest water

course into which they urinate or defecate in order to wash afterwards. Thus

a rite, originally intended to foster cleanliness, has been turned into a ,.oat

dangerous practice. This occurs in spite of -ohamaedan condemnation of the

pollution of water courses with human exoreta, unless the volume of water is

large and the flow is considerable, which is not true of most of the irrigation


Mosley (1951) writes that "Bilharsia snails must have water, and they

prefer stagnant conditions. In addition, they require feed. The principal

conditions which interfere with those essential requirements are flood and drought.

In many parts of Africa widespread flooding in the wet season is succeeded by

severe desiccation a few months later. Many places are too current-ridden at

one time of the year and too dry at another to support snails at all. In

fact, over much of the continent, it is 3nly during short periods of stagnation

at the beginning and end of the rains that the snails find conditions of life

really suitable. That brief period is sufficient for a small, scattered, and

largely innocuous population of Physopsis, 3iom:3halaria, and Bulinus. Thus a

widespread low-grade population of dangerous snails mainta-r:s itself. This

forms the basis of large populations of dangerous snails when, through changed

circumstances, opportunities arise.

"Such opportunities arise when man interferes with the landscape, and

more particularly when he interferes with drainage. The object of irrigation

projects is to smooth out the peaks of flood and drought. Similar effects

arise from the construction of road, railways, and dams. Both the structures

themselves, and the works arising incidentally from them, such as excavations

left behind after the work is finished, give the snails protection from flood

and drought. The presence of large numbers of human beings is also a factor,

since it inevitably results in the waters being polluted. As a result of these

changed conditions the dangerous snails increase in numbers and then there is

an outbreak of bilharzia."

During our survey of conditions along the Shire, we were impressed with

the abundance of habitats favorable for the development of the snail hosts of

schistosomiasis. Along the shores of Lake nyasa wave action is sufficiently

strong to prevent the establishment of the vector snails, Physopsis globosa

and Biom halaria pfeifferi. This is not true, however, behind the lake shore

in the pools and swamps which border parts of the lake. We were able to collect

the snails in great abundance in a pool at Chipoka and from a swamp at the south-

eastern edge of the lake. Other swamps behind the lake shore as well as those

behind the shore of Lake Malombe also had large populations of the snails.

In the dambos adjacent to the Shire and the uiet parts a the r� ver itself

where vegetation was dense, snails occurred in ab%;ndance. This *.as t in

the Upper River as well as in the Lower River. There -eroe scarcely :~ny habitatsa

where the snails might be suspected of baing present that we were not able to

find them. They were particularly conspicuous where there were concentrations

of people using the water for bathing, drinking, and other household usoe. It

was not surprising to us, then, when we learned of the extremely high incidence

of bilharsia.

The question arises as to the possible effects of the. stabilization of

Lake Nyasa and construction of an irrigation system. Stabilization of the lake

will preserve the marginal swamps and pools and thus suitable conditions for

the activity of the snails throughout the year will be maintained. This means

active transmission of schitosomiasis throughout the yaar. It is likely That

transmission slows down or ceases at the present time during the dry season in

parts of the country.

Similar conditions will be produced along the Upper Shire follzoing

stabilization for the swamps will be flooded for most of, if not the entire year.

In the Middle River, only the very quiet portions of the impounded water will

provide suitable habitats for the vector snails.

Irrigation of the Lower Shire and the Elephant Marsh will also provide

wider opportunities for year round transmission of bilharzia. Now the swamps

may dry out for at least a few months of the year. With the irrigation project

in effect, habitats will be provided for year round transmission. Whether this

is of consequence or not is unknown, for with the widespread infections, the

problem is extremely difficult to evaluate.


There is no really effective way known for the elimination of the disease

in primitive areas. The crux of the situation lies in the prevention of

access of human excreta to water which will be used untreated by other humans.

If this could be accomplished, the battle would be won; however, sanitary

disposal of human wastes might solve part of the problem but not all. Promio-

cuous urination and defecation, particularly by children, is widespread and

it would be especially difficult to make an illiterate population conscious of

the needs for even primitive sanitary measures. In spite of the difficulties,

education to make the people aware of the danger of fouling drinking and bathing

water might go far toward helping solve the problem.

Snail destruction offers another approach to a solution. There is as yet

no molluscicide that can be considered to be truly effective in eradicating

snails without upsetting the balance of nature. During a conversation with

Dr. 0. MacLean, U.A.C.A., he told us of his work on bilharzia control on Likoma

Island in Lake 2yasa. The population on the island numbers about 5000 individuals

who are nearly all literate and have some understanding of the disease. When

he began his work, about 60% of the people were infected and this number has

now been reduced to about 10%. His control project, which involves killing

snails by the use of copper sulfate, has been under way for about a year. The

situation on Likoma island is somewhat different from that of the mainland for

the disease is isolated and the water to be treated is considerably limited.

The high degree of literacy also contributes to the success.

Some newer molluscooides are being tested and these offer promise in con-

trolling or eradicating snails in a limited area. Results with the newly

developed from santobrite are particularly encouraging. For the most effective

use of snail control, comprehensive surveys are required to locate endemic

centers of the disease, then the molluscocides could be applied to all water in

the vicinity in which the species of snails involved in disease transmission

- i-

were living. In our opinion this is a less satisfactory way of dealing with

the problem than through the process of education, but at least use of this

method would help reduce the degree of transmission and might, in local areas,

actually cause it to recede. Dr. JacLean's work shows that education plus snail

control will work in local areas.

Correlated with education and snail control, another, and possibly the

most effective control procedure, would be to supply all towns and villages

with sanitary drinking and bathing water. This would be very effective in

those places some distance from streams and ponds. Without thorough indoctrina-

tion of the population in excreta disposal, provision of sanitary water might

have little bearing on reduction of infections, in those people living along

the banks of the Shire. It would be much easier for them to visit the river

than to wait in line at the village wells. It is obvious that the disease is

a rural problem for in cities with pipeborne water supplies, the cycle is broken

and the incidence falls to practically nothing.

We should like to recommend that a survey of the incidence of bilharzia

in the Shire River Valley be undertaken with the aim of determining those

places which should be dealt with first. After this has been completed and a

system of priorities set up, various steps should be taken& provide the

villages with properly encloses wells, preferably with some sort of simple

hand pump so that the water is completely inaccessible to them except by pumping;

make certain that sanitary latrines are provided for all persons and empower

the native authority to enforce the use of the latrines; fence waterways near

villages to keep people out of the water. In addition to these actions,

drainage of pools and swamps whenever feasible should be practiced. We believe

that educative techniques will yield the greatest return and of these motion

pictures are the best. Films made with native actors and narrated in the local

dialects in si-ple language can serve to drive home the points that must be

emphasized. -e are of the opinion that if these films are shown to the same

natives at least three times in rapid succession that the lesson will be ab-

oorbed. Viewing of the film should be required.


The following recommendations are made with the aim of developing a

long range program to better health conditions in the Shire River Valley as

the project to improve this region through engineering changes advances. As

there may be a considerable time lapse between the submitting ot the recommenda-

tions and their implementation, many may have to be re-evaluated in the light

of new techniques that are developing today at such a rapid rate.

A. Establish a Division of Preventive Medicine under the Director

of the Medical Services. As one of its major aims, this

division would conduct thorough epidemiological surveys to

determine the prevalence of diseases throughout the Shire Valley.

It would also be charged with the supervision of vector control.

B. Under the Division of Preventive Medicine, there should be a

competent malariologist whose duty would be to investigate the

malaria problems of the Shire Valley prior to the engineering

developments and to supervise and integrate a comprehensive

malaria control project in those areas in which he deems such

work to be necessary.

C. Appoint an entomologist familiar with medically important insects

in tropical Africa. He should be instructed to carry out bio-

logical studies of the insect vectors discussed in this report,

as well as others that might become dangerous with changed con-

ditions. The entomologist should be thoroughly familiar with the

latest mosquito control techniques and should apply them in his


D. Although we realize that funds are limited, the preventive

medicine branch should be su.:.lied with all necessary facilities

It is cheaper in the long run to prevent diseases than to hav-

to treat them and to have them constantly sapping the vitality

of the populace.

E. It's standard engineering practice in any manipulation of the

lake-river system, devise and apply means to prevent the develop-

ment of foreshore banks and the accompanying longshore lagoons,

which seem to us a major factor in the ecology of some of the

most important diseases that afflict the riparian villages of the

Shire Valley.

7. Specific recommendations with regard to malaria, onchocerciasis,

trypanosomiasis, filariasis, and schistosomiasis are listed in

the discussion of these diseases.


Annual Reports of the Medical Department, Nyasaland. 1929-1950.

Arnold, C.'.B. 1952. Lake Nyasa's varying level. 'yasaland Journ. 9;1)i 7-11,
1 table, 1 diagram.

Baker, J. K. and 'fhite. 1947. Southeast Contrai Africa popuilati3ns. Giooraphical
Journal, 108: 198.

Berner, Lewis, 1950. Sntomological Report on the development of thoe Uiver Volu
basin. Government of the Gold Coast.

Blair, D. 1. 1952. Bilharziaois survey of British South Africa. :yasaland Annex
13. WHo/aAL/58/AFR/aAL.

Chwatt, L. J. 1949. Memorandum on malaria incidental to irrigation projects in
West Africa, being a comment on the British Wlest African Rice mission'ss report
1948. Mimeo.

Cooper, *.G.G. 1947. The geology and mineral resources of Nyaealand. Geol. Surv,
syasaland Bul. 6: 3-9, 2 maps.

Debenham, Frank. 1938. Report on tha water resources, etc.; The 'yasaland ?rotector-
ate. His Uiajesty's Stationery Office (Col. Res. Publ. No. 2) op 55-64, 2 7raphs,
3 maps.

De Million, Botha. 19?7. The Anophelini of the Ethiopian Geographical region. Publ.
S. African Institute for Med. Rea. Johannesburg. No. XLIX.

Faust, E. C. 19,9.* Hiuan Helminthology. Lea and Febiger, Philadelphia.

Garnham, P.C.G. and J.P. dMciahon, 1946. The eradication of Simuliiu neavi4 7oubaud
from an onchocerciasis area in Kenya colony. Bull. ent. Res. 371 619-t27, 2 figs.,
6 tbls.

Gopsill, W.L. 1939. Onchocerciasis in Nyasaland. Trans. Roy. Soc. Trop, {ed. XXI
(4)s 551-552.

Griffin, A.E. 1946. A report on flood control and reclamation on the Lower Shire
river and other specified areas in Myasaland. Publ. by the Crown Agents for the
Colonies, London, pp. 1-37, 6 diagrams, 4 maps.

Johnston, H.C.J. 1949. The weather. :yasaland Journ., 2(2): 30-34, 2 figs.

Kanthack, F.E. 19-8. Report on the measures to be taken to permanently stabilize
the water level of Lake Nyasa. Govt. Printer, Zomba (Myasaland), pp. 1-26, 13
tables, 1 graph.

Lamborn, W.A. 1925. The seasonal habits of the common Anopheles of Myasaland. Bull.
Ent. Res. 15�4)! 3((-3-7. 1( ?.

Mattingly, P. F. 1952. The sub-genus Steg gig (Dipteral Culicidae) in the Ethiopian
region (Part I). Bull. Br. Muse (Nat. Hist.), Entomology. 2(5)s 235-304. 16 figs.

Mosley, Alan. 1951. The snail hosts of bilharzia in Africa, their occurrence and
destruction. H. K. Lewis and Co., Ltd., London.


Muirhead-Thompsor., T.C. 1947. Iecant knc-ledeo abo;.t malaria vectors in West Africa
and their control. Trans. Roy, Soc. Trop. '4ed. Hyg. ,0(4)i 511-527.

Russell, .2. F., L. S. West, and R. D. 'ianwell, 1946. Practical lalariology. W.3.
Saunders Co., Philadelphia.

Tennessee Valley Authority. 1947. Ualaria control on inpoiunded water. Super-
intendent of Documents. Washington.

Van Someren, V.D., and J. McMahon. 1950. Phoretic association between Afronurus
and Siarmlium species, and the discovery of the early stages of Simulium neavei
on freshwater crabs. nature , 166 (*217)s 350-351, 1 fig.

Wanson, 4., L. Curtois, and B. Lebied. 1949. L'eradication du Simulium damnosum
(Theobald) a Leopoldville. Ann. Soc. Med. Trop. 29(3): 373-403, 2 tbls., 1 graph.

Waneon, M. and C. Henrad. 1945. Habitat at comportement larvaire du Simulium
damnoeum Theobald. Rec. Trav. Sci. ded. Congo Belge. 'Jo. 4: 113-121.


1. The Shire River at Liwonde.

2. The Shire River at Matope.

3. Marginal vegetation along the Shire River near 'tundu.

4. Elephant iarsh showing relationship of vegetation and water.

5. Elephant Marsh,

6. Collecting adult mosquitoes from a native house at :tundu.

7. A drying pool north of Fort Johnston. The pool teemed with larvae of

Anopheles gambiae in July.

8. A drainage ditch west of Chileka in which Anopheles and Culex larvae were


9. Mkhasi stream in August. Larvae of several species of mosquitoes

including Anopheles funestus were collected here.

10. Close-up of an algae-filled puddle beside the Nkhasi stream. Anopheles

funestus larvae were common.

11. A bathing area at the edge of Elephant Marsh. Both Anooheles and

Taeniorhvnohus larvae were collected in the vegetation.

12. A close-up of the Asolla mats present around the edges of the pool shown

in photograph 11.

13. A close-up photograph of Pistea whi3h harbors Taeniorhynchus and

Anopheles funestus.

14. A tributary of the Shire River about ten miles east of Limbe. Simulium

larvae were found where the water was flowing swift.

15. Fish weir set in a small stream near the Shire River at latope. Larvae

of Simulium damnosui were collected in the swiftest part of the stream.

16. A backwater at Chipoka cut off from Lake Nyasa by a sand bank. Ideal

breeding conditions are provided for Anopheles funestus and bilharzia


17. A stick taken from the backwater shown in photograph 16 to which several

snails of the genus Phvsopsis are attached.

Graph showing mean annual rainfall at three stations in the catchment

area of the Shire River.

Graph showing the correlation between rainfall and the numbers of

Anopheleg Gambie Giles collected in the Fort Johnston region. (From

Lamborn, 1925).


Biotic Comaaunitiea of the Shire Valley Hydrosere

(The following outline is obviously sketchy and incomplete. The region is little
known ecologically and even an elementary account of habitat structure and
occupancy must await a great deal of further faunal, floral and hydrological
study. It has nevertheless seemed worthwhile to include the present preliminary
resume, based on the journals o our two-month survey of the river and on the
scanty literature available, as a gazetteer of the ecological situations noted
and a crude synthesis of all data at hand at the end of our study.)

Important Minor Habitats

Communities of the Shire Bed

A. Open water communities

1. Lotie situations

Medically IinDortant


a. Quiet reaches; smoothly flow-
ing water

Eroding bottom

Silting bottom

open water
clean sand bottom
submerged shelters
stems and leaves of
-rooted millfoil

Planorbis (occasional)

Milifoil beds

Pila (?). Anodonta.
Abundant cichlidYand catfish fauna.
-crocodiles; Pelusios; softshell turtle.
hippo; otter; water mongoose cormorants
(reed and white-breasted); anhinga;
pink-backed pelican; African sea-eagle;
osprey; kingfishers (pied, giant,

b. Rapids

Sliding rapids in bedrock
Stage rapids on broken bed
Confused rapid on boulder
Rapids eroding new alluvium

Algal mate

submerged shelters
algal streaiers
trailing Phragmites tips
scoured root-masses of

Simulium griceicolle

Simulium damnosum

mayflies; stoneflies

pmII ortant Steer il s

c. Falls

Spray community
Cascade pools

Pothole community (deep chim-
neys in cliff tops, cut at
times of higher level and
holding permanent water)

wet rocks
rook crevices
liverwort mats

Duckweed mat; open water.
submerged shelters;
bottom mud and debris

Simulium griseieolle
Simuii damnoeau

Anopheles gambiae
Anopheles fuaestas

mayflies; stoneflies

qctiscid, haliplid and hydrophilid
beetles; limpets; Rana; clawed frogs;

2. Lenitic situations

Embayment lakes

Sloughs and oxbows

Longshore lagoons

karsh ponds and pools

surfwashed sand bottom
stable silt bottom
submerged shelters
stews of rooted plants
pads of ~riphaeay
Pistia cups
rafts of Asolla, Spartina -
and duckweeds
beds of i tricularia and Cerato-
bottom mud and debris
masses of filamentous algae

Physopsis; Planorbis

Anopheles gaabiae
Anoxpeles funestue
Anopheles pharoensis
Anopheles coustani ziemani
Anopheles coustani tenebrosus
Taeniorhynchus africanus
Taeniorhynchus uniforms

B. Litteral succession

Sand beach
newly silted shore
new natural levee
anchored sudd (rafts of Phramites,
and other grasses and sometimes
Papyrus, bound with herbs and
creepers: Pistia fields)

stems and leaves of emergent
plants, under and out of water
fibrous rootmasses of grasses
saturated stable silt
saturated sand
rocks or logs at water*e edge
cavities in bluff banks
quiet watet among plant stems

Anopheles gambiae
Anopheles funestus
Anopheles pharoeneis
Anopheles coustani zioeani
Anopheles coustani tenebrosus
Taeniorhynchus africanus
Taeniorhynchus unifor:r.is

various families of aquatic HOMiptera and
beetles; various genera of Odonata and
mayflies.Lianea; bivalves (Anodonta);
Rsna spp.; hippo; water mongoose;
Melanoides (?); Pila (?)

gray-headed gull; black rake; African
moorhen; lesser gallinule; African jacana;
African dabchick; gray heron; purple heron;
African yellow-billed egret; squacco heron;
little bittern; hammerhead; South African
pochard; African black duck; dwarf goose;
knob-billed duck; greater flamingo

bivalves (Anodonta); Ampullaria;
treefrogs (Hyperolius, Uegalixus) Rana spp.-
various sandpiper and plovers


~--~-~C--L rs~--rr -~-r- - ---

mI portant Minor Rabitate Natic s

Phragmites fringe
PaniouB fringe
Typha shore
Drifting sudd
Eroding bank; mud, sand or
rook; shelving, steep or

II Riparian and floodplain succession
(succession, cultural history and
relation to fire little understood;
includes some of best soils of the
Protectorate and is mostly in active

A. Sudd-fields

B. Typhs marsh

C. Dimba (inclined marsh)

D. Dambo (marsh flats to wet savanna;
partly edaphic, partly controlled by
fire which favors grasses, which in
turn choke out tree-seedlings)

E. Palm savanna (grassland on coarse or
rocky alluvium, with scattered or
clumped palms (Hphaene, Borassus)
baobab, mgoza (Sterculia)and others)

nilotic monitor

surface of sudd
interior of suddmass
water beneath suddmass
submerged stems
water among submerged
emergent stems and leaves

ecology variable with
seasonal and cultural in-
fluences; niches ranging
from lacustrine to terres-
trial and augmented by
those associated with cul-
tured maize, rice, cotton,
cassava, peas, beans, se-
same, bulrush and finger
millet, sweet potatoes, sor-
ghum, ground nuts and bananas

Anopheles cambiga various weavers and swamp warblers; various
Anopheles funestus snipes; marsh harrier (see also birds of
Ana7hele pharoensis littoral succession)
Anopheles coustani ziemani
AnopelAs coaetani tenebrosus
Anopheles nili

hippo; duiker; waterbuck.reedbuck

mamba; puff adder
gray-footed squirrel; galago

F. Savanna woodland

1. Nsangu savanna woodland Copen woodia-id
with Nsangu (Acacia albida), ntondo troeholes
(Cordyle), sausage tree (Kigelial hollow trunks and logs

Aedee aegyptLi
Aedee africanus

I l_ . . .



Importnt Minor Habitats Medically Important

and scattered groves of amumo
palm (Borassus). Soil light
alluviumi, ranging from seasonally
dry to permanently wet, mainly
under cultivation)

2. Tsangu savanna woodland (Widely dis-
tributed, especially along Middle
Shirej short grass on infertile
soil with often nearly pure stand
of tsangu (Copaifers mopane)

rotting logs
nmamal dung
termite mounds
fluctuating waterheles
banana axils
grass and arboreal
hippo tracks

Aedee siso
Glossina morsitans

game country sable; kudu; impala; eland
bushbuck; warthog; bush pig

3. Napini parkland (Low forest dominated
by napini (Terminalia service),
often in pure stand, with some grass
in understory; extensive on sandy
alluvium of east side of lower

4. Combretua-Acacia orchard savanna
(Open woodland on coarse, recent
alluvium, with tall grass, domin-
ated by several species of Acacia,
Cobretun, ebony (Dalbergia) and
others. Subclimax under strong
fire control because of dense tall

G. Tree swamp (Ware and of limited extent); wet trunks
seasonally aquatic to terrestrial subaprod debris
swamp forest, with chiwale palms (Rahpal a4raal niches
nyowe, muso (species of Syzvyium) and

H. Evergreen fringe (gallery) forest (Gda-
phic climax dominated by mbawa (haya
nyasica) or kweranyani (Piptaaenia) on
deep alluvium, or by mwenya (Adin ) on
rocky shore)

(mainly terrestrial)
rotting logs
leaf mold

AeIpC aegypti
Aedes africanus
Aedes simosoni
Glossina brevipalpie
Black-lipped cobra

collared sunbird; scrub bulbul; rufous-
tailed bulbul; little green bulbul;
Heuglin'r cossypha; white-spotted weaver
finch; Livingstone's turacou; Cape
broadbill; Natal robin-chat; green-
becked bush warbler; puff-backed shrike:
vervet monkey



Important Minor Habitats Uedicallv Important

III. The Tributaries

A. Permanent streams (small minority)

1. Headwaters

Wet cliff faces
Valley head seeps
Rheocrene springs
Rocky creeks
Wooded plateau streams
Plateau savanna brooks

helocrene springs
wet leaf drift
algal and liverwort mats
current-swept shelters
shelters in quiet places
"trout" pools
pot holes

Sinuliuu neavei
Simuliup damnneum.
Anopheleau qabia
Anopheles funestus

Plaari~; stoneflies; myflies; Odonata;
limpets; crabs
trout (introduced)

2, Lower reaches (ecology as of Shire proper)

B. Intermittent streams

Flood gulleys
intermittent ravine streams
Lower tributaries with permanent
Dry lower valleys
Sand rivers, subsurface flow per-
manent or seasonal

damp ravine bottom
damp soil under stones or logs
permanent pools
(aquatic stages as for above)

SimuliurL damnosum
fAnopheleg gamibiae
Anopheles funestuas:

waterboatmen; back swimmers. Kassina;
Phrygoaaruw (frogs)
Nilotic monitor

University of Florida Home Page
© 2004 - 2011 University of Florida George A. Smathers Libraries.
All rights reserved.

Acceptable Use, Copyright, and Disclaimer Statement
Last updated May 24, 2011 - - mvs