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52 chemicals that did not show
maximum killing power in short exposures to have increased effectiveness with
longer contact. Heptachlor was the
only exception to this, indicating that the shorter exposure times were sufficient for it to demonstrate maximum effectiveness. The length of exposure
is an important factor in determining the degree of effectiveness of any one
of these compounds. Also, an idea of the extent of repelling
action of chemicals on earwigs may be indicated by higher mortality resulting
from enforced contact with the insecticide than
where an option exists. The field
experiment using granules showed that an excessive dosage of all chemicals
was applied. However, due to difficulties involved in calibrating the
application apparatus to a smaller output, it was impossible to obtain a
dosage less than four pounds to the acre. It might be noticed, nevertheless, that the greatest
differentiation among the chemicals took
place in the first five days after treatment. The two chemicals showing most rapid control were heptachlor
and dieldrin. These, in turn, were
followed by aldrin and chlordane. It is noteworthy to mention that
this order is not comparable to that obtained from laboratory experiments
where heptachlor proved to be inferior to aldrin. However, the relative dosages in the laboratory experiments
were different and thus an accurate comparison cannot made. |