162 
PREVENTION AND REMEDY. 
A judicious rotation of crops is so simple and complete a pre¬ 
ventive measure, that remedies for injury to corn by the north¬ 
ern corn root worm are practically unnecessary. The eggs being 
laid in corn ground in the fall and the larvae hatching the fol¬ 
lowing spring, feeding so far as known upon nothing else but 
corn, the planting of such infested land to any other grain must 
inevitably lead to the starvation of the young when they hatch 
in spring. This is not an inference from the life history of the 
insect merely, but even before the time and place of oviposition 
were known, it had been commonly noticed that corn was rarely 
if ever liable to injury by this insect if planted on ground which 
had borne any other kind of crop the preceding year. I have, 
however, some reason to suppose that sorghum and broom corn 
are not good crops to follow with corn when this root worm is 
present. 
The frequency of the rotation must depend upon circum¬ 
stances, and especially upon the general abundance of the insect 
at the time. I know of no part of Illinois in which corn is not 
safe for at least two vears, and in manv situations another 
year may be added to this period. No field on which the crop 
has already suffered to any noticeable extent should be planted 
to corn the following year; and it will likewise be prudent to 
avoid continuing in corn any field in which the grass-green beetle 
of this species is seen to be abundant in September and October. 
The only other preventive measure worthy of mention is one 
equally to be commended as a general agricultural practice; 
namely, the maintenance of the fertility of the soil by the use 
of manures, etc. This will not, so far as known, diminish in any 
way the amount of insect attack, but it will enable the plant to 
stand a minor injury with relatively little loss. It is possible 
that experiments with various kinds of fertilizers will show that 
some of them, the potash salts for instance, may have an im¬ 
mediate deleterious effect upon the larvae in the earth, but we 
have at present only a speculative basis for this supposition. 
Description. 
Larva (Plate XIV., Fig. 7; and Plate XV., Fig. 2-8).—The 
corn root worm, when fully grown, just previous to its last 
moult, is .4 of an inch in length by one tenth that width, white 
and smooth when under a low power, but when more highly 
magnified, the skin is seen to be minutely roughened with very 
small tubercles. The body is cylindrical, narrowing a little an¬ 
teriorly, the first segment being the shortest and narrowest of 
all. There are a few scattered stiff hairs to each segment, most 
numerous anteriorly, and especially upon the head. The latter 
is narrower than the first segment, convex but flattened above, 
about two thirds as wide as long, and smooth except for the 
hairs already mentioned. It is yellowish brown, a little darker 
