Trapping Studies On Glossina Longipennis Corti At Nguruman, South-Western Kenya

ABSTRACT

Studies have been carried out at Nguruman, south-western

Kenya, on Glossina longipennis Corti, a little known member of

the fusca group of Glossina. The first objective was to

develop an efficient trap suitable for both sampling and

control purposes. Studies were then carried out on the

population dynamics of G. 1ongipennis using the newly

developed sampling methods. Lastly the trap/odour bait system

was tested in a control situation.

Replicated Latin square design experiments were used to

compare the performance of various trap designs and odour

attractants. The Zimbabwe F3 trap proved more effective than

the widely used biconical trap, especially for females. A new

trap developed at Nguruman, called the NG2B, was also very

effective and had the advantage of being cheap and easy to

construct. Acetone and cow urine together increased the

catches by 4-5X over unbaited traps, but when dispensed alone

neither of them was effective. There was no significant

difference between the attractancy of cow urine and buffalo

urine. Trap catches were further increased when l-octen-3-ol

was dispensed together with acetone and cow urine. A higher

proportion of older flies was caught by the NG2B trap compared

to the biconical but no significant difference was observed in

the age structure of flies attracted by different odour baits.

The effect of trap design on sample composition and the

potential for using odour baited traps for sampling the fusca

group of tsetse flies are discussed.

An electric screen adjacent to a baited target was used

to determine the precise activity pattern of G. longipennis

which is known to be crepuscular in behaviour. Morning

activity started at about 15 minutes before sunrise at 0630 h,

peaked at about 0615 h and ceased by 0700 h. The species was

more active in the evenings, when activity began at about 30

minutes before sunset at 1815 h, peaked at 1845 h and ended by

1900 h. Males were regularly active before females. Light

intensity was found to be the most important factor

influencing activity. The relationship between activity

pattern and cattle-fly contact is discussed.

Changes in the apparent densities of G. longipennis were

monitored simultaneously using biconical and NG2B traps in two

areas located 7 km apart. Both trap types showed similar

trends in population changes but higher apparent densities

were recorded with the NG2B trap than with the biconical trap.

Apparent densities in both sexes were regularly observed to

increase during the rainy seasons and decrease during dry

seasons. Peak catches in one area were observed to precede

those in the other area by one month. Flies spread out to more

open areas during the cool wet seasons and concentrated in the

thicker woodland during the dry seasons. The factors

influencing changes in population densities, including

movement between the two areas and between vegetation types,

are discussed.

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.X

Mortality rates estimated from ovarian age structure and

from Moran curves were observed to be highest during the hot

dry seasons and lower during the cool wet seasons. Adult

mortality rates showed a significant positive correlation with

maximum temperature and a negative correlation with minimum

relative humidity. The effect of fly movement on mortality

rate estimates and the reliability of the estimates by the two

methods are discussed.

Dissections of female flies from NG2B traps showed that

all non-teneral but nulliparous females and over 80% teneral

females were inseminated. The average percentage distribution

of the various pregnancy stages in trap samples were found to

be very close to the values expected from the duration of the

different stages, in contrast to the usual underrepresentation

of flies with third instar larvae for other

tsetse species. The average abortion rate was 6% but ranged

from 0% in the rainy seasons to 60% in the hot dry season. A

significant negative correlation was observed between abortion

rate and minimum relative humidity. A significant positive

correlation was also found between fly size and minimum

relative humidity of the previous month but one. A discussion

is given of the immediate causes of abortions and their

effects on population levels and of the factors influencing

fly size.

x l

The absolute population size of G. longipennis was

estimated through mark-release-recapture experiments. The mean

population size was estimated at 17,300 males (range 10,471 -

25,703) and 16,900 females (range 14,125 - 20,892). The trend

of changes in the absolute estimates corresponded with those

in apparent estimates from trap catches. From the peaks in the

recapture rate of marked flies, the feeding cycle of G.

longipennis was found to be 2-3 days for males whilst for

females the 9-10 day pregnancy cycle was the main factor

affecting the recapture rate. There was a considerable amount

of movement of marked flies between the two sampling areas but

the movement was shown to be greater in one direction than the

other.

A trial tsetse population suppression operation with

baited NG2B traps was started during the course of the study.

After 11 months of operation, the population levels of G.

1ongipennis were reduced by about 60% for males and about 90%

for females. Much greater reduction levels were obtained for

G. pallidipes. A discussion is given of the factors

influencing the lesser impact on the population of G.

1ongipennis with suggestions on improving methods for the

control of the species.