practically no influence on the biting activity and only a short heavy downpour or a longer rain reduced and even stopped the biting

numbers

for that

^time.

56 Ada Trop. XXVI, ^{1, 1969}— Medical Entomology

AUGUST OCTOBER

1966

I

-»--"•>

NOVEMBER JANUARY

1967

I -J

FEBRUARY APRIL

r _xA

MAY JULY

i I I

645 7 8 9 10 11 12 13 14 15 16 17 161815

HOUR OF THE DAY

Figure^{4. The} variation of the biting cycles in the 5. damnosum population under the influence of seasonal _changes.

Häusermann, ^{On the} Biology of ^S.damnosum ⁵⁷

300

o o 200

z ^IOC

m i/i

z ^(/1

0 _-o

in <

El i/i -]

£ S

6

i

3 s

(/IO 2/10 4/10 6/10 (/10 10/10

CLOUO COVERAGE IN TENTHS OF THE WHOLE VISIBLE SKY

Figure^{5. The} influence of the light ^{conditions on the} biting activity of ^5.

dam-58 Acta Trop. XXVI, ^{1, 1969}— Medical Entomology 4.6.

Distribution

and dispersal 4.61.

Distribution

The perennial

larval

habitats _on

which

^S. damnosum larvae can ^be

found in

late

dry

^{season are restricted to} rapids in larger streams, mostly in medium ^and lower altitudes. ^iVt the _same time

biting

^{flies are}

mainly

caught in medium altitudes ^and not

in

lower altitudes where the

larval

habitats are more favourable. When the

biting

^{numbers increase}

after

the

first

rains, the increase ^is more remarkable

in

medium altitudes though ^the

larval

numbers

increase

first

in the

larval

habitats of the lower altitudes.

Only in

^the

second

half of

^the

rainy

season, when the upper parts

of

the streams discharge more water and the non-perennial

rivulets

start to

flow

again, the breeding of ^{5. damnosum} spreads over the whole area of the Mahenge mountains shown on map ^1.

Differences

in biting

^{numbers between the 8} catching ^stations of the

flyround in ^different

^altitudes, shown on table ^7, and

occasional observations in other localities

permit

^the

following

generalizations

on the

distribution

of ^5. damnosum

in

the eastern

part

^of the Mahenge mountains.

In

altitudes between ⁵⁰⁰ and 1000 m ^{above sea} level the

biting

densities are the highest

throughout

the year

in

this _area and the highest

biting

^{numbers are recorded}

for

clearings

in

^the forest or

Table ^7. Biting densities at different catching stations of ^the flyround

Daytime

Chirombola 8.00-8.20 ¹ 1.0 0 1.6 0.2 0.3 23 0.7

Mselezichini 8.40-9.00 26 4.5 0.1 1.1 1.3 1.2 78 2.3

Lupanga^{shule 9.20-9.40 69 11.1 0.3 2.8 6.5 4.7 227 6.7}

Chiwambu 10.20-10.40 ^{130 18.5} 0.9 1.8 37.7 24.0 ⁶³¹ 18.5

Liatu 11.40-12.00 ^{54 14.3} 1.3 1.8 26.3 18.3 421 12.5

Mbangayao 12.40-13.00 63 8.3 0.1 2.1 1.0 9.2 192 5.6

Nasanji 15.20-15.40 29 7.8 1.4 2.9 16.3 1.7 217 6.3

Isongo juu 16.00-16.20 6 0.8 0.7 1.5 0.7 1.5 41 1.2

Totalnumber of^flies

per period ^{378 389 34 124 540 365 1,830 6.7}

FMH/per quarter ofyear ^{8.0 0.6 2.0 11.2 7.6}

* FMH flies _per man-hour.

Häasermann, ^On the Biology of^S. damnosum ⁵⁹

woodland used

for

^rice

cultivation

(e.g. Chiwambu,

Liatu).

^{On the} bottom

of

^the _valley the

biting

^numbers are usually smaller ^(e.g.

Lupango ^shule, Mbangayao), although ^here record

biting

^numbers

are also possible

during

^the period of highest population density.

In

lower _parts of the valley, below about 500 m

biting

^is

by far

not

so frequent, even when the

biting population

^{is at its} peak, e.g.

Mselezi chini, Chirombola.

Further in

^the plains, ^{S. damnosum is} occasionally caught on man

during rainy

^seasons

only

^and e.g. in Mwaya, ⁹

km from

^the next

larval

habitat, not noticed by ^the people.

In

higher altitudes over about ¹⁰⁰⁰ m

biting

density ^is again decreasing compared to medium altitudes (Nasanji ca.

950 m, Isongo

juu

^{ca. 1050 m),}

^but

^{5. damnosum and S. woodi are} occasionally caught up ^{to 1500 m (highest} altitudes

in

^the

Mahenge massif).

¦4.62. Dispersal

An upwards directed

migration

^of

newly

hatched females may extend over 20-40

km -

the largest distances between the ^favourable

larval

habitats

in lower

altitudes to

biting

localities in the upper ^{regions —, whereas the} random dispersal

from

the Mahenge mountains

into

^the surrounding plains ^{seems to be} negligible. The extremely low

biting

density on the catching station Chirombola,

within

²

km

distance

of

two favourable

larval

habitats, demonstrates

this. Inside the Mahenge mountains, however, the dispersal

activity

^{must be} regarded ^as very ^intense.

Marking

experiments were conducted on

four different

places

from

March to May ¹⁹⁶⁷ in order to gain some

information

on dispersal

activity.

^{33 430} flies caught on human

bait

were marked and released. 312

of

these were caught again

within 0-9

days after release and in distances of

0-5 km from

the

point

^{of release.} The biggest distance

of

_approx.

5

km

was covered by an uninfected _parous

fly

^{in not more than}

6 hours, ^i.e. at ^14.00 h after release of the

first

batch of ²⁵ marked

flies

at ^08.00 h

in

the _same morning. Another

fly

^{was caught37a}

^km from

^the point of ^release not more than 9'A hours after

marking.

The results of the

marking

experiments are shown

in

^{table 8 and} on map ^3. The recaptures demonstrate

that

^{S. damnosum} covers considerable distances in

biting

mood, may ^be

in

direct

pursuit

^of human

bait

_or

following

the numerous footpaths connecting the various hamlets

with

the ricefields on the _slopes.

When the

biting population

^started to decrease, suddenly

extremely high numbers of

biting

^flies were caught again

after

some weeks of low

biting

^numbers.

It

^is possible that

immigration of

larger ^numbers

of

flies

from

other _areas,

probably from higher

60 Ada Trop. XXVI, ^{1, 1969} — Medical Entomology Table8. The results of the marking experiments

Table 8 a. Preliminary marking experiments

Date Place Kindof

14. 9.66 Lupanga by hand onthorax

12. 11.66 Mbangayao by hand on thorax

31. 12.66 Mbangayao by spray ^{190 3. 1.67}

5. 1.67

11. 1. 67 Mbangayao by spray ²⁰⁵ 15.1.67 264

17.1.67 ¹⁸⁵ nulliparous

Table ^{8 b.} Marking experiments for dispersal (see also map ³⁾

Date Place Number Marked recaptures in distance

marked from point of release

0.5 km ¹ km ^{2km 3km 4}km 5 km

Mbangavao 5,711 ⁶¹ 29. 3. 1967

1 nulliparous

** ¹ _parous, ¹ nulliparous.

*** ¹ old _parous.

Häusermann, ^On the Biology of ^S. damnosum ⁶¹

Map ^3. The results of the marking experiments.

altitudes, ^induced

by

cooler temperatures, ^is responsible

for

this sudden increase

in biting

ⁱⁿ a decreasing population.

The

marking

experiments demonstrate ^also that ^S. damnosum females may remain

nulliparous for

a considerable period

after

a

first

unsuccessful attempt ^{to get a bloodmeal.}

Preliminary marking

Im Dokument On the biology of "Simulium damnosum" Theobald, 1903, the main vector of Onchocerciasis in the Mahenge Mountains, Ulanga, Tanzania (Seite 28-34)