Virginia citizen. (Irvington, Va.) 1891-1921, 1901-07-05
LIFE HISTORY OF A PARASITE.


cludipg the human, are wonderfully
intelligent and absolutely remorse-
less; they must be so to successfully
carry on their affairs. But the insect
kinds, being little things and preying
upon little things, do not at once i'm
press us with feeling of repugnauce,
and indeed they are so generally
found to be beneficial to mapkind
that We must call them friends.
think that it can be safely stated
that the majority of the insects at
tackled by parasites are noxious
species. Indeed, it is probable that
no moth or butterfly larva is without
its parasitic enemy. To the insect
thus preyed upon nsturalists have
applied the term "host," and the
manner in which these unfortunate
larvae become tenanted by living,
squirming, voracious blooksuckers,
that sap upon their vital organs and
eventually kill them, is very interest
ing. A medium. sized ichneumon
will choose for its host a larva that
grows just large enough to serve the
purpose of nourishing its larva, and
thus. generation succeeding genera
ton, the parasite will remain true to
its host, though no doubt, if the
host could be consulted, it would
wish its admirers should prove more
tickle.
Que of the daintiest of our COM
mon insects is the pretty little COL
Jared grapevine moth, formerly in
cluded in the genus Procris. This
moth is deep blush black, the only
touch of bright color being an orange
or yermilion band or collar surmount-
ing the thorax. Grapevines are its
most common habitat, and feeding in
small colonies, each being the hatch.
ing of one batch of eggs, aud each
caterpillar being possessed with the
usual caterpillar appetite, it is very
natural to find some portion of the
vine with its leaves rapidly disap-
pearing, one by one. Indeed, were
itnot for our friends, the wren and
the parasite, our grapevines would
soon practically cease to exist. And
as efficient as the admirable little
wren is, | believe the parasite plays
the more important part. So sue
cessfully warred upon are these
pretty little pests that it is doubtful
II any large vine supports an average
of more than half dozen cater
pillars of Procris that reach maturity.
A small brachonid fy, pale yellow
in color, with large black eyes, the
individual parasite of the grapevine
moth, has heen given the name of
RhOgas harrisiaae.
Decidedly the most interesting part
OF the tragedy between Rhogas (Which
resembles giant mosquito) and
Procris (the caterpillar) is the
beginning Of it, when, after the
female of the former, with unerring
instinct, has hunted diligently for
the larva of the latter, she happens
upon a colony of her victims. Back
and forth she has searched, under
and above each leaf, walking excited
ly as if on springs, her long antennm
(long soft horns) incessantly twitch-
ing and touching the leaves; flying
from leaf to leaf and exploring with
a thoroughness that would do a
trained bird dog credit. She makes
straight for her game when found
and proceeds at once to business. To
prove she has come upon those of
the right breed, her powerful scent
organs, the antenn@, with seemingly
caressiDg touches, inspect the cater
pillars, which in turn at once show
alarm, swinging their heads from
side to side, as means of repelling
attack. But such means are vain.
Straddling the first lowly caterpillar,
with her stilt-like legs reaching too
far out on each side for interference
Rhogas curls her flexible, segmented
abdomen downward and forward and
thrusts her keen stinging ovipositor
deep into the squirming victim, and
upon the instant a minute egg is
forced through the ovipositor and
under the skin of the caterpillar.
The ovipositor is then withdrawn and
the fly seeks another victim close by.
repeating the operation till her egg
supply is exhausted, having perhaps
parasitlzed a dozen or twenty worms,
IN one or more colonies. But these
sword thrusts of the ovipositor do
not kill the caterpillar outright, nor
of themselves result in death.
Natures little plan would here mis-.
carry if such were the case. The
victims 90 righton living healthfully
for time. But when the eggs are
hatched. each caterpillar becomes the
host of tiny white grub with a
truly terrible appetite. This is the
larva Of the Rhogas. The grub feeds