66 SOME INSECTS INJURIOUS TO TRUCK CROPS. 
It will be seen that arsenate of lead, even when applied at an 
excessive strength by hand or machine sprayer, was entirely ineffec- 
tive against the larvae of D. virginica on sugar beets and celery. 
Paris green, when applied very thoroughly by hand to celery, gave 
perfect results when used at excessive strengths, but when applied 
to sugar beets with a machine sprayer (the only practical method 
with such a crop) it, too, proved ineffective. 
The failure to kill the larvae was not due to their being nearly 
mature, as in the earlier experiments they varied in size all the way 
from one-fourth to three-fourths grown; and as the development of 
this species is very irregular there were larvae present which were 
not over half grown when all the experiments were made. 
Judging from the results of these experiments, the arsenicals can 
not be depended on to control the larvae of D. virginica on sugar 
beets. It is evident that clean cultural methods offer the best chance 
of keeping this species under control. The larvae are very general 
feeders, and during the early growing season they evidently prefer 
weeds, such as lamb's-quarters, for food. Much benefit would be 
gained by keeping the ditch banks, and spaces along the fences, 
free from weeds. 
On reaching maturity the larvae crawl under heaps of dead weeds, 
tufts of grass, boards, and other rubbish, along the ditches and 
fences. In such quarters, which, especially in the case of weeds and 
grass, offer but slight protection, they construct frail cocoons in 
which the pupae pass the winter. There is no better method of fight- 
ing this species than to burn the weeds, grass, etc., under which the 
pupae find protection. This burning, which can be done any time 
between November 1 and April 1, would not only have the advantage 
of destroying quantities of weed seeds and Diacrisia pupae, but would 
also kill the " alkali bugs" (Monoxia sp. ?) which hibernate under 
the weeds in the same places as the Diacrisia pupae. 
In the field the larvae were watched for over three weeks, or until 
a large proportion of them had matured and left the plants to pupate. 
The arsenate of lead was visible on the beet foliage during all of this 
time. A few larvae were put in a cage supplied with the poison- 
coated leaves from the sprayed plats immediately after the applica- 
tion was made. These leaves were almost completely consumed 
during the following two days and after that unsprayed foliage was 
given them. Only one small larva out of about 25 died, although 
they were kept caged and under daily observation for ten days or 
until the oldest individuals began to prepare to pupate. 
Personally the writer believes that the failure to kill the larvae 
was due, in part at least, to the fact that an insufficient amount of 
spray was used to the acre. Fully 100 gallons to the acre should 
have been applied. 
