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50

series of experiment I, because of slower reactionary characteristics, would afford a better illustration of chemical activity on the nymphal stages of earwigs. Although the length of chemical weathering was not the same for all dosages in the secondary series, this difference did not cause a change in the effectiveness of dieldrin, which stood out from all the rest. The superiority of dieldrin in both rapidity and extent of kill at all dosages is noticeable throughout the succeeding laboratory experiments.

Considering the overall effectiveness demonstrated with all dosages in the majority of experiments, aldrin turned out to be second to dieldrin. In the rare cases where aldrin did not prove more effective than chlordane or heptachlor, the range of difference was very slight in the effects of all three chemicals, and they may be regarded as showing equal effects.

The problem is somewhat changed in the overall picture with the last two chemicals, chlordane and heptachlor. They were found to show similar characteristics in some cases and to differ greatly in others. Heptachlor showed a greater effect in most of the primary series of all experiments, and could justly be considered as the third most effective of all chemicals with respect to initial kill. However, it gave the least effect of all chemicals in the majority of the succeeding series and apparently had the least residual life of all chemicals tested. On the other hand, because chlordane and heptachlor parallel each other to a marked degree as regards residual life, for all practical purposes these are comparable at the dosages used. The superiority of heptachlor over chlordane following initial treatment showed heptachlor to be somewhat superior to chlordane.