The herald-advance. (Milbank, S.D.) 1890-1922, 1908-07-31
THE e BUG,

he attacks Of numbers Of ~predaceous
and parasitic enemies. Among the
former are Syrphid flies, two-winged
insects. which place their eggs among
the colonies, the eggs Matching inta
hungry maggots which consume large
numbers Of lice. The socalled lady
BIRDS beetles belonging to the family
C~occinellidae. do the same thing, their
grubs or young %devouring enormous
numbers OF aphids.
Among their parasitic enemies the
most prominent, In fact the parasite
through whose work in normal years
both Toxoptera and Macrosiphum are
kept in check, Is a small four-winged
hymenopterous insect, Lysiphlebus tri-
tici which. upon the advent Of warm
weather IN the south last summer, rap
idly increased and reduced the hordes
OF lice. This insect we found In the
north, last summer, and reared 1t ro-
peatedly from ~Toxoptera. Unfortun-
ately l.. tritici does lot reproduce
freely at low temperatures; below
So degrees F. it is said to be inactive.
or, as Webster puts It, 1t Is active only
when the temperature is 25 degrees
above that at which the green bur
breeds freely. The method OF attack
on the part OF this parasite is shown
in Fig. 2 Of one Of our illustrations.
and represents an individual OF
Lysiphlebus sp. In the act of oviposit-
ing in a specimen Of M. granaria.
Normally l.. tritici, as observed by us.
approaches ~Toxoptera very deliberate
ly, generally from behind, though fire.
quently from the front, and o~viposits
with but little, or at least without eff
fective resistance on the part OF that
louise; but Macrosiphum e to
be more on the defensive, and a foe
requiring finer tactics. This may ac-
count for the method Of attack an
shown. The egg placed in the body
OF the louise, matches in a few DAYS.
The larva feeds upon the tissues of its
host, preventing, it is claimed, any
great production Of young, and in this
way, even before the death Of its host,
doing much to check the increase Of
the pest. Later, about a week from
Matching possibly the parasite has at
tanned its full size, and with the prop
er light and magnification. can be dis
tinguished through the body wall Of
It's host, Fig. 3. The body Of the louise
swells, the individual dies, the skin
darkens and hardens, and in q short
time the little parasite energies az Z
four-winged fly from a round hole cut
in the abdominal wall of the dead in.
sect, Fig. 4, prepared to mate and
carry on the good work, If only the
weather will permit. Millions Of this
genus of parasites are in our fields.
working not only upon Toxoptera,
when present, but upon some other
plant lice, notably Macrosiphum, and
i ordinary years are the principal
means Of keeping these pests in
check. 1t IL an encouragement to
know that young lice destined to be
winged are frequently parsitized:
hepce, when the image migrant dies Ia
other fields. it frequently carries the
beneficial insect with It It IL worthy
of note also in connection with the
Of parasitism. that We ind in
the north climatic conditions which
are directly opposed to any disastrous
outbreak OF grain plant lice. In other
words. we have cold winters and warm
summers. the nYst factor preventing
any undue increase OF lice unattended
BY parasitism. and the warm sum
mers allowing of q = rapid fncreaoa
Of parasites before the lice have
much hsadway.