Sheep treated at Onderstepoort with emulsions containing 5 per cent.
and 2•5 per cent. para para isomer of D.D.T. on selected sites on the
fleece, and subsequently tested on these treated sites by artificially induced strikes with first-stage larvae of blowflies, were protected for a period of approximately three months.
A field experiment in the Graaff-Reinet district of the Karroo is described
in which sheep were sprayed in the breech region with emulsions containing 6 per cent., 5 per cent. and 2•5 per cent. of the p.p. isomer of D.D.T. A considerable degree of protection was afforded which was more apparent on
sheep pastured on Karroo veld than on those running in lucerne lands.
The conclusion arrived at is that the treatment of sheep, according
to the method described, with a D.D.T. emulsion containing 5 per cent.
of the p.p. isomer will afford a degree of protection sufficient to reduce
blowfly strike to a minimum during the periods of greatest activity. Treatment
is best applied shortly after the first summer rains about September and again after the late summer rains in February.
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