10 BULLETIN 1426, U. S. DEPARTMENT OF AGRICULTURE 
The color of the adult varies with age and hardness. The fresh 
callow adult is almost cream-colored and requires several days to 
become chitinized. As the insect hardens the color ranges through 
dull yellow and various shades of red-brown. The old, fully matured 
adult is a very dark pitch-brown, sometimes almost black; the head, 
prothorax, sides of body, and venter always a shade darker than 
the elytra, which almost always have a distinct red-brown tinge, even 
when very dark. The legs and antenne are light red-brown, the 
antenne paler on club. Kyes and mandibles black in the mature 
form. The smallest specimen seen measured 1.82 mm. long by 0.82 
mm. wide; the largest measured 2.6 mm. by 1.18 mm. The aver- 
age is about 2.2 mm. by 0.92 mm. 
Secondary sexual characters are very obscure; the male head tends 
to be narrower than the head of the female. There are apparently 
no reliable characters for distinguishing between living males and 
females. 
SEASONAL HISTORY 
EARLY SPRING ACTIVITY 
Clover root borers usually pass the winter well down in the roots 
of the clover plants on which they were nourished during their larval 
life of the preceding season. The great majority at this time are 
fully matured adults and remain more or less dormant, either singly 
or in small groups, in enlargements of the larval mines. Adults 
which for any reason have become separated from clover roots may 
pass the winter in the soil or, rarely, under trash on the surface of 
the ground. Occasional larve, usually well grown, are found during 
the winter in larval feeding burrows. Apparently these are larvee 
which hatched from eggs laid in the late summer of the preceding 
year. 
‘When the soil warms up to a temperature of about 45° F’.” in the 
early spring, the activity and feeding of the adults and the few over- 
wintered larve are gradually resumed in the roots. More or less 
activity probably occurs also during the winter when temperatures 
are high enough to permit of metabolism. The adults work their 
way from the lower parts of the roots towards the crown, where they 
are often found congregated in March and April. They feed on the 
root tissues and their so-called fat bodies begin to develop. As the 
soil temperatures rise above 50° F. this activity becomes more pro- 
nounced, and when the temperature of the air at the surface of the 
ground is between 55° and.60° F. the borers often leave the roots 
and walk about. This form of activity may rarely take place on 
warm days in February, from plowed-up clover and dead clover 
roots, but usually occurs in late March or early April and on days 
later in the spring when air temperatures range below 65° F. In 
case of a cool, backward spring, this movement of the beetles on foot 
is the only method of migration to new host plants until late in the 
season. 
In clover fields plowed up during the preceding summer and fall, 
soil conditions, and the disturbed, abnormal state of the residues of 
the clover root borer’s host plant, induce premature activity of the 
7 Temperatures for field observations were recorded from portable air temperature thermometers and 
portable soi! thermometers. Observations made on the laboratory grounds were correlated with stand- 
ard Weather Bureau maximum and minimum thermometers, a Friez hygrothermograph, and a Friez 
soil thermograph, the bulb being buried 3 inches under growing winter wheat. 
