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19

experiment, which was due in part to the changed environment and to the fact that older earwigs are more difficult to kill. The recently applied materials produced a rather substantial kill but there was a decided loss of effectiveness in the later series. Dieldrin showed a 97 per cent kill in the first series and 88 per cent in the second. Aldrin was second with a 61 per cent kill at first which diminished to only 11 percent in the second series. Heptachlor acted quite rapidly early in this experiment but apparently had little lasting effect. Chlordane showed less than 50 per cent kill in the first series and did not give any effect in the second.

The third group of experiments was conducted late in the season using adults only. The conditions of the work were the same as in experiment II except that there was a 22-day lapse between the first and second series. The results are given in figures 7 and 8. The same trend continued to show, indicating that the older earwigs are harder to kill than the younger ones. The control with dieldrin was more complete than with the other materials, but none of them performed well. Dieldrin killed 67 per cent of the earwigs in the first series but only nine percent in the second. Aldrin killed 61 per cent in the first and about 11 per cent in the second. Heptachlor and chlordane killed less than 50 per cent in the first series and were ineffective in the second.

Effects of the medium dosage

The medium dosages were calculated to approximate the usual commercial dose and were twice as strong as those used in the previous section. The same three series of experiments were conducted under the same conditions as before except for some differences between the timings of the second group of tests.