30 BULLETIN 1426, U. S. DEPARTMENT OF AGRICULTURE 
to too few roots. The total progeny of one pair in each case recov- 
ered from 12 cages of this type was, in cages containing one root, 13, 
14, 9, 16, and 9, in the season of 1917; in those containing two roots, 
13, 16, and 15 in the same season; in those containing three roots, 4, 
21, 14, and 21, 1n the season of 1918. For all cages of this type the 
average progeny of a single pair is 13.75. 
The square screen cages placed on the ground over five clover 
plants furnished practically optimum conditions for reproduction. 
Unfortunately, however, these cages allowed access to other borers 
from below, in case any had wintered over on the spot of ground 
selected for a cage. As it was discovered that a control cage suppos- 
edly kept free from root borers contained infested roots, some of the 
records for this type of cage were disregarded. However, one cage 
of this type was examined early enough (July 25, 1918), to be certain 
that only the one female had had access to the roots. In this case 
a pair of borers in copulation had been introduced into a cage on 
March 20; when the cage was examined July 25, 19 larvee in all stages, 
2 pupee, and the living female parent were recovered on four of the 
five roots. The beetle, when dissected, contained 1 half-grown and 
3 immature eggs in shrunken, depleted ovaries. She therefore showed 
an actual progeny of 21, or an estimated possible progeny of 25. In 
1920 particular care was taken to bar out of the cages all root borers 
other than those intentionally introduced. In one of these experi- 
ments a cage which contained a verified pair of borers, placed in it 
May 3, contained, when examined August 11, 4 pupe and 4 larve 
on one root, or a total progeny of 8. Another true pair, placed in 
another cage May 6, yielded 4 pupz and 5 larve on August 11, or a 
total progeny of 9. Three similar attempts with single females swept 
in flight failed to produce young. 
From a survey of the conditions attending these experiments, it is 
believed that the most reliable information as to the rate of repro- 
duction results from the use of the cylindrical wire-mesh cages con- 
taining three clover plants, in soil known to be free from infestation. 
In each of two cases in 1918 the maximum progeny thus obtained 
was 21. A reliable result is also thought to have been reached with 
the cubical wire-screen cage examined before the death of the parent 
female, in which were found actual progeny numbering 21, or esti- 
mated possible progeny of 25. In all experiments the borers were 
protected from natural enemies and were on clover plants in partially 
shaded ground, the cages being covered with cheesecloth. These 
conditions were believed to be more favorable to root borer activities 
than would be the case in plants in soil under natural conditions. It 
is therefore deduced that the total progeny of one female in nature 
rarely exceeds 25 in number, and probably averages considerably 
fewer than that. 
It may therefore be concluded from the foregoing data on the repro- 
ductive activities, life history, and seasonal history of this insect that 
it is a slow and by no means prolific breeder, and that if some of the 
existing agronomic practices, together with its protected mode of 
life, were not favorable to its undisturbed increase, it would not be 
a widespread, destructive pest. 
