1. Higher concentrations of the new organic insecticides are necessary to
achieve a complete kill of first instar larvae of Lucilia cuprina Wied., when contact
with the insecticides is short than is necessary for mature larvae. The former
are able to free themselves rapidly from the toxicant in the nutritional medium
owing to their feeding habits.
2. The larvicidal action of eleven synthetic insecticides has been studied and
the minimum lethal dose determined on young maggots within a nutritional
3. A new biological assay method for determining the larvicidal value of wool
treated with various insecticides has been developed.
4. Insecticides of equal toxicity to first stage blowfly larvae afford different
lengths of protection against strike even when their active ingredients are of the
5. The importance of the larvicidal properties of insecticides in protecting
sheep over long periods is stressed as of very much greater importance than the
more transitory repellent properties to adult blowflies possessed by such insecticides.
6. The biological assay method has revealed that a number of insecticides such
as gamma BH.C., Dieldrin, Aldrin and to a lesser extent Chlordane and Toxaphene
possess properties of diffusion which permit of their penetration from
previously treated wool on sheep into the constantly expanding zone of growing
wool. Compounds of the D.D.T. group do not diffuse along the wool fibres.
7. The duration of protection of sheep afforded by any insecticide is dependent
upon the larvicidal value and diffusion power of the particular insecticide. For
this reason gamma B.H.C., Dieldrin and Aldrin have been found to be the compounds
most suitable for this particular purpose.