1. Three groups each of twelve merino sheep were treated separately with
Lindane in emulsion, suspension and dust form to determine the influence of
the formulation on the duration of protection against blowfly strike.
2. The emulsion and suspension contained a wetting agent of anionic type.
The emulsion, containing 970 p.p.m. gamma B.H.C. and the suspension with
940 p.p.m. gamma B.H.C. were applied by immersion in a small vat of 120 gallons
(546 litres) capacity. Twelve sheep were used for each formulation. The removal
of dip wash per animal and the depletion rate of the insecticide were determined.
3. The rate of depletion of insecticide from the dipping bath was higher
per sheep treated in the emulsion than in the suspension. This is supported by
the finding that the average deposition of Lindane per sheep was 30•6 grams for
the emulsion, but only 16•9 grams after immersion in the suspension.
4. The percentage rate of exhaustion of insecticide continued to rise progressively
as the absolute quantity available in the tank decreased. This rise in
percentage depletion was far more marked in the case of the emulsion that the
5. There was no significant difference between the amount of insecticide
deposited in the fleece of the first and last of twelve sheep treated in either the
emulsion or the suspension formulation. This may be ascribed to the finding
that in the case of the emulsion the progressively higher percentage depletion
accounted for the higher rate of deposition in the wool, in other words the higher
rate of selective removal. In the case of the suspension the lower absolute
depletion rate together with the appreciably lower percentage removal were the
factors involved in maintaining the even deposition of insecticide with the progress
of dipping. Had more sheep been dipped the end result would probably be
6. Continued immersion of sheep in an emulsion dip will result in a sudden
and rapid complete depletion of insecticide below the level of biological effectiveness.
Using a suspension dip it will take longer to reach this point.
7. Using a non-returnable spray as the means of applying an insecticide a
suspension spray must be mixed at 2 ½ times the concentration of a dip and an
emulsion of anionic type at about 5 times the concentration of a dip to obtain
the same concentration of insecticide on treated sheep.
8. Attention is directed to Laudani's observation that the amount of insecticide
absorbed by wool is dependent not only on the concentration of the active
ingredient in the dip wash but also on the absolute amount present. Full consideration
must therefore be paid to the capacity of a dip or bath.
9. The third group of animals was treated with dust at a rate of 17 gm.
of the active ingredient per head, i.e. the amount absorbed by each sheep dipped
in the suspension, in order to facilitate comparison of larvicidal efficacy of a dust
and a suspension. The bio-assay tests with first instar maggots of Lucilia cuprina
revealed an average protection of relatively shorter duration, 29•4 weeks with the
considerably heavier deposit (30•6 gm.) in the case of emulsion, than the 27•4
weeks with the suspension (16 • 9 gm.) and 29 • 8 weeks for the dust (17 gm.).
The dust, therefore, gave the best protection of the three formulations per unit
of insecticide absorbed by the fleece.
10. The grease content of the fleece was shown to exert a marked influence
on the degree of efficacy of the insecticide deposited from an emulsion. This does
not apply, however, in the case of the dust or the suspension. The loss of
larvicidal activity is proportionate to the level of wool grease which is not affected
by dipping or spraying.
11. The quality of the wool has no effect on the protecting properties of any
of the formulations.
12. The use of B.H.C. or any compound possessing good powers of diffusion
in the wool is recommended for the long term protection of woolled sheep against
blowfly strike. Such compounds may be used in the form of dusts or wettable
powders but the present investigation suggests that their use as emulsions is