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was found to be more prevalent in Maryland near the District line 
than on the grounds of the Department of Agriculture. In the latter 
place there was practically no infection worth mentioning. 
A very large proportion of cabbage loopers was affected by the 
minute parasite Copidosoma truncatella, perhaps 15 per cent during 
September, but none in earlier and less in later months. 
Observing that the larvee were most extensively affected by the 
Copidosoma parasite in a region badly infected with rot, a number 
of healthy larve were placed on potted cabbage affected with both 
the bacterial and brown rots, while others were kept as a check lot 
on fresh cabbage, this experiment being made to ascertain if the rots 
were in any way responsible for the diseased condition of larve. 
Somewhat to the writer’s surprise it could not be seen that the 
larvee placed with the diseased plants were affected in any manner 
more than those kept under the same conditions with perfectly healthy 
plants. 
The melon plant-louse, Aphis gossypii Gloy., affords a striking 
example of the combined effects of weather and natural enemies in the 
control of an insect. Of all common plant-lice this species appears to 
be most susceptible to climatic variations. During moist or humid 
weather, particularly in the early portion of the summer, this species 
is capable of propagating in the greatest numbers, but during pro- 
tracted heated and dry spells, such as happened in the season of 1900, 
its natural enemies, which are legion, are able to keep it almost com- 
pletely under control. During the year it was not reported at this 
office as doing any damage save in one locality in Nebraska, a State in 
which it does as much if not more damage than any other in our 
country. In the year 1899 this species was very destructive in the 
States of Florida, Texas, Maryland, Virginia, Pennsylvania and 
Georgia, and District of Columbia, while the previous year it did dam- 
age over much the same territory, as well as in Kansas and Arkansas, 
injury being particularly pronounced in Texas. 
SOME GENERALIZATIONS. 
Asa result of study of the subject of the effects of weather upon 
different species of injurious insects which occur in the neighborhood 
of the District of Columbia during the past year in connection with 
observations that were made the previous year the writer has deduced 
certain conclusions. One of these, not expressed in the earlier article 
on this subject, is that there is a tendency on the part of introduced 
forms to develop one or more generations in their adopted habitat 
than native northern species produce, a habit which conduces very 
largely to their destruction, resulting in a corresponding decrease in 
their numbers. 
