6
THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY. [V,
METHODS EMPLOYED IN KEEPING AND FEEDING FLIES FOR LABORATORY PURPOSES.
In transmission work with blood sucking flies, great difficulty has been ex-
perienced in maintaining the flies alive under laboratory conditions for a desired
length of time. This is due mainly to the fact that it is almost impossible to provide
them, in the laboratory, with the same conditions as are available in the field. Con-
sequently a high rate of mortality often results even if kept together in cages for a
short time. Again, the work of inducing them when under confinement to feed on
animals is equally difficult, involving considerable labour and patience.
In order to overcome these difficulties various methods for keeping the flies
alive under laboratory conditions and subsequently feeding them on experimental
animals have been employed by Dutton and Collaborators [1907], Stuhlmann [1909]
Baldrey [1911], Mitzmain [1913], Francis [1914], Cross and Patel [1921], Connal and
Connal [1922], Nieschulz [1926—29] and Kranefeld [1931].
Before starting the experiments recorded in this paper, the author' tried several
methods for keeping the flies of T. orientis and S. calcitrans under laboratory condi-
tions and after numerous trials the plan finally adopted was to keep these flies singly
in glass tubes measuring four inches by one inch (Text-fig. 1, figs. a. 1, b. 1). The
tubes were plugged with cotton-wool, and the lower half of each was lined on the
inside by blotting paper moistened with water, so as to enable the fly to suck
moisture during such time as the paper remained wet. When dry the blotting
paper served the purpose of absorbing the excrement of the fly. The flies did no
appear restless in the tubes and could be kept alive in this condition for a few
days preceding the experiments.
The collection of flies for each experiment was carried out on healthy animals
while grazing. The flies on being collected were enclosed separately in tubes and
when brought to the laboratory were kept in the manner described above. The
flies employed in all the experiments were starved for eighteen to twenty-four hours
prior to the feed on infected animals, with the object of eliminating, as far as possible,
natural contamination, i.e., contamination by which it would be possible for them to
act as mechanical carriers.
In the majority of the transmission experiments with blood sucking flies, so far
reported, it has been the aim of the workers to feed them in large numbers at one time
on an infected animal, and after a desired interval of time to allow them to suck the
blood of a healthy animal for the production in it of the infection. Moreover, for the
infective feed in these experiments, the flies have been allowed to have a complete
meal, or alternately feeding has been interrupted in the infected animal, the rest of
the meal being completed on the healthy animal.
Although en masse feeding of flies is convenient and saves time, it is not a very
suitable method, for, there are no means of estimating the number of flies that have
actually fed on the animals under experiment, and in the event of infection being
transmitted, the number of flies responsible for its transmission remains unknown.