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37

to 25), 100 per cent mortality was achieved with all chemicals at the heavy dosage, and the length of time required for complete kill was considerably shorter than with the other dosages.

A somewhat similar picture is shown in experiment III, where again the heavy concentration surpassed the medium and light to effect a better than fifty per cent kill in every case. These results are shown in figures 26 to 29.

There was relatively little differentiation between the effects of the medium and light dosages of all chemicals. In all cases, the medium and light dosages paralleled each other more close than either of them did the heavy dosages, which had results quite widely separated from the other two.

Recovery from the effects of chemicals

Figures 30 to 33 show typical examples of cases where recoveries did occur during the process of the experiments. These figures also show that in early stages of the experiments there tended to be a higher proportion moribund; and as the experiments progressed the proportion of moribund individuals diminished. There were fewest recoveries from the light dosages of the chemicals, the full significance of which is not understood.

Exposure time and chemical potency

A fourth experiment was conducted to determine the relation between the length of time that earwigs were exposed to the four chemicals and the rapidity and completeness of kill. Earwigs were exposed for periods of one, five, ten, 15, 30 and 60 seconds to a medium concentration of each chemical. This was done in treated plastic test tubes in the manner outlined on page 12 in the section on Methods