Pierre weekly free press. (Pierre, S.D.) 1889-19??, 1908-07-30

the attacks of numbers Of predaceods
and parasitic enemies. Among the
former are Syrphid flies, two-winged
insects, which place their eggs among
the colonies. the eggs Matching into
hungry maggots which consume large
numbers of lice. The so-called lady
birds beetles belonging to the family
Coccinellidae, 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 aud Macrosiphum are
kept in check, III a small fouSswlnged
hymenopterons insect, Iysiphlebus tri-
sici 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 th.
north, last summer, and reared 1t re-
peatedly from Toxoptera. Unfortun-
ately l.. tritici does not reproduce
freely at low temperatures; below
30 degrees T. it is said to be inactive,
or, as Webster puts 1t, it is active only
when the temperature is rs degrees
above that at which the green bug
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 oyipostt-
ing in 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 oviposits
with but little, or at least without eff
fective resistance on the part of that
louise; but Macrosiphum appears to
be more on the defensive, and a foe
requiring finer tactics. This NAV ac-
count for the method Of attack aa
shown. The egg placed in the body
OF the louise, matches in a few days.
The larva feeds upon the tissues of it's
most, preventing, it is claimed, any
great production OF young, and in this
way, even before the death of it's host.
DONG much to check the increase of
the pest. Later, about 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
its host, Fig. 8. The body of the louise
sWells, the individual dies, the skin
darkens and hardens, and in short
time the little parasite energies as a
four-winged fly from 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
In ordinary years are the principal
means Of keeping these pests In
check. 1t is an encouragement ia
know that young lice destined to be 4
winged are frequently parsitized:
hence, When the image migrant flies to
other fields, 1t frequently carries the
beneficial insect with it. 1t is worthy
of note also In connection with ths
subjects of parasitism, that we find In
the north climatic conditions which i
are directly opposed to any disastrous
outbreak OF grain plant lice II other
words, we have cold winters and warm
summers, the first factor preventing
any undue increase OF lice unattended d
by parasitism. and the r.n gu n.
mers allowing Of a a rapid increase /
Of parasites before /, lice !,
gained much Roadway.