70 
BULLETIN 1476, U. S. DEPARTMENT OF AGRICULTURE 
During the early spring some of the larger and more substantial 
weeds, such as Xanthium, Arctium, and Polygonum, frequently con- 
tain a greater number of larvae per plant than is shown in Table 
20. Many of the larvae contained in large weeds at this time have 
migrated during the late autumn from more fragile weeds such 
as Echinochloa, or from the remnants of near-by cultivated plants. 
During the spring of 1922 a total of 203 larvae were taken from a 
single plant of Xanthium and 75 larvae from a single stalk of 
Polygonum. 
The prevalence of the borer in weed growths has increased in 
intensity, especially since the abandonment of large-scale burning 
Fig. 34. — Typical weed area in New England, severely infested by European corn . 
borer. Similar weed areas contained over 400,000 borers per acre 
and weed-control operations. This increased infestation may be 
partly due to the reduced acreage planted to corn in the badly in- 
fested districts, but in any event during the late summer of 1922 
a series of detailed field counts showed that in three large typical 
weed areas (fig. 34) located at Cambridge, Watertown, and Arling- 
ton, Mass., and aggregating 85.3 acres in size, there were from 
277,000 to 406,000 borers per acre. The predominating weeds in 
these areas were barnyard grass, pigweed, lamb's-quarters, cock- 
lebur, beggar-ticks, bread grass, and Mexican tea. These neglected 
weed areas act as sources of infestation to the surrounding territory 
for many miles through the flight of the adults, and locally by 
the migration of larvae, 
