Dye BULLETIN 1426, U. S. DEPARTMENT OF AGRICULTURE 
ened or dying plants are the preferred food of the clover root borer, 
there is evidence that development is most rapid and secure on the 
roots of clover plants which have received a check to their vegetative 
activity. This fact was also noted by Riley (37), who stated that 
the root borer ‘‘flourishes most in the roots of plants that have been 
injured and that have already begun to decay.’’ Such a vegetative 
check usually occurs naturally in most clover regions in July and 
‘August, when the second crop of clover has matured its foliage and 
is producing seed. Summer droughts also check the vegetative 
rowth and thereby accelerate the development of the root borers. 
An artificial or mechanical check to vegetative growth is produced 
by the simultaneous attack of several root borers, whose combined 
burrows seriously interfere with the functions of the root. Checks 
to vegetative growth may also be occasioned by disease or by the at- 
tacks of other insects and may sometimes be due to a failure of the soil 
to produce the elements required for continuous growth of the plant. 
Hibernation has frequently been noted to be more successful on 
very much weakened roots or roots which have died late in the 
season and are more or less decayed than on roots still in a healthy 
condition. An indication of the disadvantage to the root borers of 
a healthy growing root as a place of hibernation was observed on 
October 4, 1917. In this case three root borers were found dead in 
their pupal cells and crushed out of shape. This fatality apparently 
was due to the partial closing up of the cells caused by the growth 
of the root before the adults were sufficiently hardened to enlarge 
the chambers. ; 
Data showing the effect of a continuous vegetative period on the 
clover root borer were obtained in observations made on the bottom 
lands along the sloughs ot Coos River and in the Coquille Valley, 
Oreg. Under conditions occurring there, clover grows very rapidly 
and probably almost continuously, because the winter temperatures 
are mild (42), the climate humid, and the soil rich and well supplied 
with moisture by a natural subirrigation as well as by considerable 
precipitation (42). Root borers are very scarce in this clover on the 
bottom lands, even in the second and third years. Yet, on the poorer 
hill soils in the same region, which are not naturally subirrigated, the 
borers are as bad on first- and second- crop-year clover as anywhere 
in the Willamette Valley. 
TOPOGRAPHY 
The distribution of the clover root borers and the damage done by 
them are often influenced by the topography of the region in which 
they occur. Low, wet, poorly drained soils, which remain cold Jate 
into the spring, retard the development oi the root borers and en- 
courage tungous diseases; but higher, warmer land may accelerate 
their development over much of the surrounding country. 
It has been observed that small farming communities isolated from 
the surrounding cultivated country by woods or wooded hills are often 
very severely infested. Often the portion oi a field along the wind- 
ward side of a grove is more severely iniested than the rest of the 
field. A case was observed where a field about one-fourth of a mile 
from an old field that had been plowed in spring, with open country 
between the two, was very severely damaged by July. On the con- 
trary, a second field, about as near the source of infestation as the 
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