Evening star., 1941-02-22
Of Stors, Men
And Atoms
Notebook of Science Progress
In Laboratory, Field
And Study
Bu Thomas r. Henry.

vast spruce forests.
II has fallen like consuming fire on
the myriads of European saWfileS Wnlcn
for the past decade have been detollat-
ing and devouring the northern woods
according to the report of entomologlSts
of the United States Department of Ag-
riculture.
The sawf1y starts life as a green worm,
the color of spruce needles. The new
disease hits it at this stage, turns II
black and causes rapid diSintegration.
The blackened skin often sticks to the
needles upon which the sawf1y had been
feeding when stricken, giving tree the
appearance of having been burned. The
sawfy's habit of making a mass attack
on a tree helps spread the disease.
The strange new insect first appeared
in the Gaspe Peninsula in Quebec in
1880. When discovered 1t already had
ravaged 1000 square miles of virgin for
est. In the next nine years this area
had been extended to 10000 square miles
in Quebec alone and the depredations
had spread to other parts of Canada and
across the United States border.
The saWfly had been known in Europe,
chiefly Czecho-Slovakia, for more than
a century, but never had been very de-
structiVe. Minute examination, however,
showed a strange difference between the
European and American insects. Both
were capable of reproducing by parthe-
nogenesis, as is common among insects.
UnfertiliZed eggs of females would hatch.
In Europe however, these eggs produced
a vast preponderance of males, which
are not very destructive and, of course,
are incapable of continuing the species.
The American broods we're almost en-
tirely females. Males were found IN
ratio of only about in 1900, The fe-
male insects were far more destructive
and every one could lay eggs from which
a big brood of destructively minded
daughters would arise. 1t seemed to be
a case in which the male had been elm
mated. The race seemed to be revertlng
to a pre-male stage of terrible destruc-
tiveness.
The best that could be done up to the
present was to hold the saWflies in
check In nine years the government of
Quebec released a quarter Of billion
other insects which preyed upon the
pests in Europe but did not damage the
spruce trees GeneticiStS were concerned
with the weird problem as to where these
destructive female hosts came from, and
failure to find their like elsewhere made
them seem almost like invaders from
another world. IN Czecho-Slovakia not
only were they dominantly males but
had quite different habits Of spinning
cocoons and different life histories. The
most logical probability was that the
bug had been introduced into Canada
from across the Atlantic, but the exist
ence of anything like the New World
type could not be demonstrated in the
Old World
When the Czecho-Slovakian insects
were studied in an English laboratory,
however, a few were found which laid
only parthenogenetic, female producing
eggs. 1t has been impossible to breed the
new type experimentally and it seems
probable that the Canadian type is found
in Europe side by side with the others.
Thus the progenies mix and the pre-
dominantly female hosts are kept rela-
lively insignificant 1t apparently was
an accident that the food of deadly
femininity fell upon the Quebec forests
without the male-producing type to keep
them IN order.
The sawf1y is now present in Maine,
Vermont, New Hampshire and Eastern
New York. Officials Of the Bureau of
Entomology and Plant Quarantine say
that where the cost is justified the in
sect can be controlled by arsenic sprays
dropped over spruce forests from air.
planes. For cheaper type of control
several types of European parasites we're
liberated in the New England forests,
but the flies continued their destructive
feeding.
The new disease was first noticed three
years ago. 1t has slowed down Sawfly
activity in many places and may prove a
permanent check on the pest, the ento-
mologistS say. There is no certainty,
however, that the check will be more
than temporary, they add. The sawfly,
reduced to comparatively small numbers
by the infection, may subSide for a few
years. Then it may emerge in large
numbers, only to succumb again to the
infection in year or two Many de-
structive insects wax and wane in such
cycles.
The sawfiy larva, the form which dam
ages spruce, resembles a caterpillar with
smooth green body and a broWnish
head, the entomologiSts say. 1t feeds pref
erably on the older spruce needles and is
a ravenous eater. Where they have
Matched in large numbers whole trees
may be stripped of their foliage before
the pests are recognized. Enough worms
feeding long enough make a spruce for
est look as if it had been swept by fire.
When mature the laNa drops to the
ground and spins its winter cocoon, from
which it emerges the next summer as
stout, black, four-winged fly, ready to
lay eggs, from which a new generation
of destructive females will emerge.
Discusses Public Neglect