The San Francisco call., 1910-06-19
By John L. Cowan

q o much has been said in recent
years concerning the depredations
~ Of insect pests that the inference
is likely TO be drawn that the
whole insect world is arrayed IN war
against the welfare Of mankind. It is
worth while. then, to call attention to
the fact that man has powerful allies,
as well as relentless foes, in the do
main OF bugs" 1t may be true that
one-tenth Of the fruits, vegetables,
cereals. forage crops and all other pro-
ductions Of the soil is exacted as a
yearly tribute to insect rapacity, but
1t is equally true that this annual toll
would be vastly greater but for the
fight waged in mans behalf by other
. insects, individually contemplate, but
collectively mighty.
The number of species Of insects in
the world is estimated at anywhere
from 100000 to 12,0O0,0O0 not more
than 100000 OF which have been de-
scribed and named. The whole world
Is aswarm with insects, varying from
microscopic size up to more than six
inches in length. Four-fifths OF all
animal species are insects, and it is
believed that more than half of the
AAOAE mass Ol animal AndLAtA GAlSllLS
upon the land surface of the globe is
locked UP in insect bodies. If all these
svarming, fighting, eating quintillions
of insects were actuated by common
hostility toward mankind human life
would be an impossibility.
But insect benehcence is not confined
to combating mans insect foes. AS
direct producers of wealth they play no
Insignificant part in the economy of
nations. The productive labor of bees,
siIkworms, fig wasps. gall flies and
other willing workers more than coun-
terbalances the destruction wrought by
the cotton boil weevil, the gypsy moth,
the army worm, the grasshopper, the
Hessian fly and the host Of insect pests,
OF which almost 1000 species have been
described and named.
There is a profound philosophy un-
derlying the inharmoniouS screed of
the near poet who wrote:
Big heas have little heas
On their backs to bite 'em;
And little heas have lesser heas-
And So ad inhntum.
1t is an understanding Of the truth
Of this-that every insect has its para
site or predatory foe that has on
numerous occasions rendered it pos
sible for the entomologists of the de-
partment Of agriculture to wage sue
cessful war upon insect foes of farm
ers. gardeners, fruit growers and others
directly dependent upon the products Of
The soil A good example is given by
the introduction Of ladybird beetles
from Japan and Hungary to combat
the San Jose scale and black scale.
The scale" is really an aggre cation of
a vast quantity Of microscopic insects
that for a time seemed to threaten
olive growing, orange growing AMI
other fruit producing industries. The
fight against scale insects inimical to
A.
ladybirds are rendering yeoman serv-
see in the interests of horticulturists,
and ultimate victory is anticipated.
No more destructive insect pest ever
threatened American harvest fields
than the grain aphis, known to scien-
lists as toxoptera graminum. In every
region In which 1t has appeared it has
been met and ultimately overcome by
its natural enemy, a small black and
brown winged fly known as the lysu-
phlebus tritici. These insects deposit
their eggs in the bodies of the aphides,
and when the eggs hatch the preda-
tory careers Of the aphides come to a
premature close. But for these natural
enemies Of the grain aphis, wheat
growing in the southwest would be
simply Impossible, and the full dinner
pail for the most Of US would soon be-
come but a memory.
The Hessian fly and the army worm
are other foes Of the farmer that sci
ence is powerless to circumvent and
industry hopeless to defeat. But when
man bows in defeat, his insect allies
bring on their cohorts and put the
enemy TO ignominious fight. The
polygnotus hiemalis seeks out the eggs
of the Hessian fly and lays its own
therein, and IN a short time each egg
so treated matches out no Hessian flies
but from 80 TO 80 parasites, and each
of the parasites gets busy hunting Hes
sian fiy eggs in which to make similar
deposits. So il happens that the Hes
sian fiy may ruin the wheat crop Of
particular section one year; the next
season il viii do but little damage. and
the third not a trace Of it can be found.
The army worm appears in myriads
and sweeps field bare of every green
thing; but il never appears twice in