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44 Residual life of chemicals in experiments II and III Tables 3 and 4 Rive the maximum per cent mortality obtained from both series of experiments II
and III, respectively. In all experiments, the second series showed a decided
decrease in effectiveness due to the longer period of time elapsed from the
chemical treatments to the time the insects contacted the chemical. In experiment II (table 3), the
light dosage showed dieldrin to have the longest residual life. Dieldrin was
followed by heptachlor, aldrin and chlordane, which had the shortest
life. In the same experiment with the
medium dosage, dieldrin again demonstrated the highest residual action. With this dosage, however, dieldrin was
followed by heptachlor, with chlordane
outlasting aldrin. At the heavy concentration, dieldrin gave the best
results, followed by aldrin, chlordane and heptachlor in decreasing order of
residual life. In experiment III (table 4), the
picture differed greatly from the previous two experiments. There was more uniformity with respect to
residual life among the chemicals in the light and heavy concentrations. With the light dosage, heptachlor showed
the shortest residual life. Next in
order came aldrin, chlordane and dieldrin.
Aldrin possessed the longest residual life of all chemicals with the
medium dosage; and it was followed by chlordane, heptachlor and
dieldrin. The latter did not show any
residual action whatsoever. In the
heavy dosage, dieldrin demonstrated the longest residual activity. Aldrin, chlordane and heptachlor followed
in order of decreasing residual life. It is interesting to note that the
order of residua11ives of chemicals in experiment II is for the most part
exactly opposite to that in experiment III. |