‘ THE CLOVER ROOT BORER 31 
ECOLOGY 
TEMPERATURE 
Many of the data that have been given indicate that the activities 
of this insect are greatly influenced by temperature. This factor con- 
trols the activities and migration of the borersin the spring. At this 
time migration from old to new clover fields is determined by the 
temperatures of the soil and air. The dates on which these migra- 
tions occur vary not only from one season to another but also from 
field to field, as borers leave clover roots in cold, wet, pooily drained 
spots several days or even weeks later than flights of borers from 
clover on warmer soil. Soil temperatures during the period of devel- 
epment determine the time consumed in the completion of that 
development. Field observations indicate that on clover in shaded 
places, such as orchards, where the soil temperatures doubtless are 
lower than in the open fields, the development of root borers is so 
much delayed that an unusual number of overwintered larve are 
found in such places in the spring. Unpublished notes made by E. J. 
Vosler at Murray, Utah, in 1912, record an unusually large number 
of overwintered larve, and indicate that the period of development 
is affected by low soil temperatures, owing to the short season at high 
altitudes, or perhaps to the cooling effects of soil moistened by uriga- 
tion. The comparatively low temperatures of the heavy clay-loam 
soils near Forest Grove, Oreg., in the spring and early summer appear 
to prolong the development of the insect to an appreciable extent as 
compared with the conditions in the spring and early summer in Ohio 
and western Maryland. 
MOISTURE 
Moisture is also an important factor in the life of the species, both 
directly and in its secondary effects on soil temperature (26, p. 220) 
and the condition of the host plant. Clover root borers in any stage 
are very susceptible to injury by dryness; even the well-matured 
adults survive but two or three days in a dry vial. All stages, even 
adults, 11 they are unable to escape, are killed by the rapid drying of 
the host roots. Ii the roots dry slowly, asin the case of undisturbed 
roots dying in early summer, adults that are sufficiently hardened to 
enaw their way out hasten to escape and find moist living roots. A 
lack of moisture in the soil affects the root borers indirectly through 
its effect on the host plant and the soil temperature. In spite of the 
unfavorable effect of dryness on the species, however, it has often 
been noted by workers that in a dry summer the root borers are 
more injurious to clover. As will be shown, the borers thrive best on 
weakened plants, such as result from droughts; not only is the mois- 
ture insufficient for the natural growth of the plants, but the acceler- 
ated development oi the borers enables them to inflict all the more 
damage. 
CONDITION OF HOST PLANT 
_ The condition of the host plant is of course of great importance 
in the life history of the insect. Although there is little evidence to 
support the theory advanced by Schmitt (39) and others that weak- 
