New York AGRICULTURAL EXPERIMENT STATION. 753 
There is also a general opinion that plant lice only thrive in 
dry seasons. It is known that some root-infesting plant lice can- 
not live except in boggy, wet land. After a heavy shower the 
Cabbage Aphis is not noticed on the cabbage as thick as just pre- 
ceding the storm; but ina day or two they can be seen swarm- 
ing over the leaves as thick as ever. The rain simply washes 
them into the folds of the leaves where they may be found piled 
up and possibly covered with water, but perfectly dry, as the 
pulverulent secretion on the body protects them. This pulveru- 
lent ashy secretion is not only a protection but makes this Aphid 
easily distinguishable from any other cabbage louse. 
History. The Cabbage Plant Louse was probably introduced 
from Europe atan early date. Dr. Fitch shows, by a reference to 
the Transactions of the New York State Agricultural Society for 
1791, that it was a known cabbage pest in this country at that time. 
Plant lice differ from most insects in that all broods are not 
produced from eggs. In general, the first brood of the season 
hatches from eggs that were deposited by the last brood of the 
preceding fall. This first brood is composed entirely of so called 
wingless females. When about eight days old they commence 
to give birth to young plant lice. The second brood is also com- 
posed entirely of so-called females. In many cases the females 
of the second brood are all winged, and they migrate from the 
plant on which the eggs were deposited to some other plant, 
where the third brood is deposited. Here two or three broods, 
all females, are produced, depending on the length of the season. 
Next follows a brood of winged females, which migrate back to 
the plant on which the eggs were deposited the previous fall, 
and give birth to a brood of true wingless females. The latter, 
after attaining their growth and pairing with the winged males, 
deposit the eggs. This, in brief, is the general life cycle in North 
Temperate regions. i 
With the cabbage louse it is an unsettled question as to how 
and where it {survives the winter. Prof. Weed* succeeded in 
finding a few eggs and males, also the egg-laying females on cab- 
bage in 1889, which he described. This is said to be the first 
description, but in the Jour. Royal Agrl. Society of Eng. (vol. 

* Insect Life, vol. Il’, page 289 (1890). 
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