During the testing of finely ground pyrethrum flowers as an insecticide for the control of Antestia lineaticollis, Stål, in coffee trees, it was noticed that the various instars showed different percentage death rates under the same conditions. The experiment which is dealt with here was primarily designed to discover the minimum effective dose of powder per tree, and was carried out as follows.

A block of 1,700 coffee trees was divided into seventeen square plots each containing 100 trees. Nine of these plots were treated with pyrethrum powder at rates varying from about 1 gram to 5 grams per tree; all the trees in the same plot receiving the same amount of powder. Two days later 36 trees from each of these plots, comprising all the trees from the centre of the plots (the two outer rows of each plot not being used in case migration of the Antestia should have taken place from the adjoining control plots) were heavily drenched with a strong kerosene extract of pyrethrum in order to bring down all the Antestia remaining on the trees; these Antestia were collected separately for each tree, sorted into instars and recorded. This method of testing is described fully by Le Pelley (1934).

In each of the eight control plots five trees selected at random were drenched with the kerosene extract of pyrethrum and the Antestia obtained were recorded in the same way. It was found that the average number per tree of Antestia and of each instar present in each of these control plots, which were themselves evenly distributed through the whole block, was practically constant. It was therefore assumed that the numbers of Antestia and of each instar was the same for the plots treated with pyrethrum prior to this treatment, and the number of each instar found on the trees after treatment subtracted from this figure represented the number which had been killed by the pyrethrum powder.