Pyrethrum extracts in non-volatile oil carriers are effective insecticides in the field because they act as a direct spray killing the insect and also form a toxic film over which the insect crawls: it is necessary to study both these effects for a complete laboratory assessment of toxicity. Suitable laboratory techniques and methods for the assessment of results are described together with an account of experiments on the effect of various factors on the insecticidal efficiency of pyrethrum-in-oil preparations, both as direct sprays and as toxic films.

The programme necessitated some duplication of work, but discussions that took place from time to time between the workers concerned at the two laboratories during the progress of the investigations reduced this to a minimum.