152 
DISEASES OF THE COTTON PLANT. 
ation ; for instance, if a female boll-worm produce five 
hundred moths, one-half of which are males and the other 
half females, the next generation, if tlie increase be in the 
same ratio, will amount^ to one hundred and twenty-five 
thousand caterpillars or moths ; and all this is ac'com- 
phshed in the space of a few weeks. It will therefore be 
perceived that their destruction depends upon prompt and 
timely action ; and planters may materially aid in carrying 
out a work designed for their mutual benefit, by minutely 
observing the habits and characteristics of these pests of 
our fields, devising means for their destruction, and com- 
municating the results of their observations and experi- 
ments, through some appropriate channels, to the public. 
Insects injurious to the cotton plant consist of those 
very destructive to the general crops, such as the boll- 
worm, cotton caterpillar, and some others; and those 
which do comparatively little injury, their numbers thus 
far not being sufficiently great to cause much damage, 
such as the leaf-rolling caterpillar (Tortrix) and several in- 
sects hereafter mentioned. There are still others, which 
do not materially injure the crop itself, such as the span- 
worm, and others which only feed upon the petals or 
pollen of the flowers. There are also many insects found 
m the cotton fields which do no damage whatever to the 
plant, but merely feed upon weeds and grass growing be- 
tween the rows, such as the caterpillar of the Argynnis 
columbina, which feeds upon the passion-vine, and that of 
the Zanthidia niceppe, which sometimes devours the Mary- 
land cassia, and produces the beautiful orange-colored but- 
terflies, seen in vast numbers hovering over moist or wet 
places on the plantations. 
A class of insects which is highly beneficial, compre- 
hends the larvae of the lady-bird, the ichneumon flies, and 
