dc.description.abstract | This study aimed at investigating the resting sites and
assessing the amount of predation done on resting adult tsetse
flies of the genus Glossina pallidipes Austen.
Tsetse flies were trapped in the field using Zimbabwean
F3 traps baited with cow urine and acetone. Flies used for
nocturnal resting site studies were dusted with flourescent
powder and released in the bush at dusk. When it was fully
dark, one-hour long searches were then made using long wave
ultra-violet light. This was done from August 1986 to May 1987.
Daytime resting sites were investigated during the hot dry and
long rainy seasons. It involved searching for resting tsetse
flies in a large field cage at four different times of the day,
namely early in the morning (05.45 to 06.30 h), late in the
morning (10.30 to 11.30 h), early afternoon (13.30 to 14.30 h)
and late in the afternoon (16.30 to 17.30 h). For each fly
observed, its resting substrate and resting height were
recorded. Temperature and relative humidity were also measured.
Nocturnal resting substrates were leaves, twigs,
branches and tree trunks. strong preferences were shown for
twigs and small branches during the cool dry, short rainy and
hot dry seaSOAS. Leaves were prelerred during the long rains.
Mean nocturnal_resting heights were lowest in the cool dry
season (1.5 m), -intermediate and equal in the two rainy seasons
(1.7 m), and were 'remarkably high-during the hot dry season
(2.3m).
Branches and tree trunks were used as daytime resting
substrates. During the afternoons of the hot dry season, the
ground was preferred, while branches were preferred during the
wet season at the same times. No tsetse were found on the
ground during the wet season. The nocturnal resting substrates
were the ones observed in the very early morning search.
Diurnal mean resting heights varied greatly during the hot dry
season depending on the time of the day. There was a gradual
decrease from 2.03 m early in the morning to 1.21 m late in the
morning, and eventually to 0.25 m in the early afternoon.
During the long rainy season resting heights fluctuated from
1.74 m to 1.38 m to 1.51 m and eventually to 1.34 m during the
four times of the day respectively.
Generally tsetse rested higher at night than in the
daytime. It was 'observed that temperatures above 250c and
relative humidity below 40% were apparently responsible for
resting low down on thick substrates, and even on the ground.
The amount of predation of resting tsetse flies was
assessed at three different resting sites namely leaves,
branches and tree trunks, and at three different localities.
The method adopted was that deyeloped by Rogers (1974). It
involved tethering tsetse flies within a 'metre cube' of the
resting substrate. The predatory behaviours of vertebrates,
mainly birds and 'lizards were watched from a distance while
those of invertebrates were done by inspections at experimental
sites. Samples of invertebrate predators were preserved in
-xvalcohol
for species identification later in the laboratory. The
amount of predation occurring in the daytime was distinguished
from that which occurred at night. The effects of prey density
on predation levels was also investigated. Results obtained
were normalized by arcsine square root tranformation and then
subjected to multivariate analysis of variance.
Field observations showed that daytime predators
largely included birds, lizards and jumping spiders of the
family Salticidae. Ponerine ants were the main nocturnal
predators. The level of total predation on the various resting
substrates, i.e leaves (44%), branches (47%) and tree trunks
(56%) were not significantly different. Vertebrate predation
was however much higher on thick substrates than on thin ones
(i.e 37% on tree trunks and 17% on leaves). Predation by ants
was indifferent Qf the sites. Level of predation in the daytime
(54%) was much higher than that at night (43%). Mean levels of
prediction at the three locations were 43%, 61% and 52%. These
were shown tg Pe significantly different. These results were
caused by the existing local differences in the abundance,
distribution and movements of tnepredator populations.
Vertebrate predation sh9wed direct density dependence
at low densities of up to 8 tsetse flies per metre cube of
vegetation. | en |