The herald., 1897-05-21
Insect Years

Every wide-awake, observing FARMER
and fruit grower is conscious OF the TACT
| that insects are often very numerous
Tor a year or two, perhaps for slhsie
season, and then the same insect may
not be noticed hardly at all for num-
ber of years. The army worm OF the
east is good Illustration of this fact.
] Occasionally, it comes in such over
whclming numbers that it destroys acres
| and acres of oats and other field crops.
Two years ago the army worm of South
| ern California (Peridroma Saucia) was
so abundant as to do irreparable dam
age in Southern California. A year ago
it wac hardly common enough to attract
any attention except from the workin2 :
entomologist. This year it has come
again in great numbers and is doing
much to lessen the profits of the orchard
| list and gardener this coming season.
The reasons for insect years are some
what obscure. In the east in case of
such insects as the chinch- bug, the hu-
nldity Of the season has much to do
with the numbers of the insects. In dry
seasons they will be very abundant,
while in wet seasons they may not be OBJ
served at ALL 1t would not be safe to say
ihat such condition may ret have .. ,
same effect here that excessive rains
would produce in the east The wet wea-
ther does not probably act directly on
the insect. though it may do SO. 1t is
more likely that it favors the develop
ment of microscopic plants or fungi,
which attack and destroy the insects
We know that here in California fungous
diseases do prey upon many of our worst
insects like the pernicious scale.
Another reason why insects have theif
ups and downs comes from their insect
enemies, both predaceous and parasitic.
The predaceous insects eat up our enc
mics while the parasitic insects lay eggs
either in or On them. and these, when
they hatch. give rise to larva that eats
I'd the plant destroyer. The minute
Chalcid flies and the larger Ichneumon
and Braconid flies belong to the latter
class. They pierce the scale or other
destructive insects, lay an egg inside
and thus their valuable work is COM
-ete. From this egg comes little foot
ess maggot-like larva. which destroys
the host. There are also two-winged
flies which are often parasitic; in form
and often in color and size these insects
fook very much like the common house
ny They are known as Tachina flies
and always lay their eggs upon the out
side Of the insects upon which they
.,rey Last evening I took members or
my entomology class to visit large Oh
i've orcnard, that we might study the
work of the new olive caterpillar. We
found these insects now over an inch
long and on many of them the little White
egg or a Iachina fly. On some of them
! We found even two eggs This means
iiiat a friend is at work in these or,
ohards. Every caterpillar that receives
Sne of these eggs is doomed. The value
62 these Tachina flies will be apprecia
led. when I state that I have often tried
% rear seventy to hundred of the east,
trn army worms and would not succeed
IN rearing one. because of the good sar-
vices of these Tachina flies The fact
that these insects are at work in on
olive orchards may we'll make lis hone
full that the new olive caterpillar will
dot do the same damage next year that
it has done this season.