Voi.. LXVIII No. 4014. 
NEW YORK, OCTOBER 2, 1909. 
WEEKLY, $1.00 PER YEAR. 
BUG AGAINST BUG. 
Insect Parasites as an Aid to Man. 
So, naturalists observe, a flea, 
lias smaller fleas that on him prey; 
And these have smaller still to bite ’em. 
And so proceed ad infinitum. 
I venture to say that when Swift wrote the fore¬ 
going doggerel he had scarcely the faintest concep¬ 
tion of the amount of real truth he had actually hit 
upon in those few lines. It is only through the more 
modern studies of present-day entomologists that 
we are coming to realize the great good done the 
farmer" and fruit grower by the many kinds of large 
and small insects that live upon and destroy other 
and injurious insects. ' Only yesterday I received, 
from a woman, a letter accompanied by some insects 
that had been caught on maple trees, and which she 
said were boring into the branches and killing them. 
The insects enclosed told a most interesting story. 
There were two kinds, one of which, called the 
pigeon horn-tail, laid an egg that hatched into a grub 
that did bore long tunnels through the branches of 
the trees, thus killing them. But the other species 
of insect, called the Ichneumon-fly, was one that 
actually hunted out the burrows of this tree borer 
and laid an egg in each of them just where the tiny 
grub that hatched from the egg could easily find the 
destructive borer and feed upon it, sapping its life 
THE ICHNEUMON FLY. Fig. 477. 
and finally killing it. Moreover, the correspondent 
had found three of the Ichneumon-flies to one of 
the pigeon horn-tails, so that it seemed as though 
the trees would be saved without any effort on the 
part of the owner, and in a much more effective and 
economical manner than any human agent could 
devise. Here then we have a splendid instance in 
which one “bug” fights another “bug” and so holds 
the bal ance in nature. 
Although it is a much-repeated saying, yet it is 
true that nature tends, in the long run, to hold a 
balance. That is, no one plant or animal or one 
fungus or insect can long increase in very great 
numbers or long hold the ascendency because its 
enemies will sooner or later appear and hold it in 
check. In other words, nature will maintain a balance. 
But the questions so often asked to-day are, if the 
parasites and enemies of insect foes exist everywhere 
why, when a new insect enemy appears, can we not 
artificially introduce some parasites or diseases and 
destroy the enemy? Has this been done, and if so, 
why can it not be done again? 
In reply to these questions I would cite one notable 
instance in which an exceedingly injurious insect has 
been held in check and almost exterminated by the 
introduction by man of another and predaceous insect. 
1 his is the case of the famous cottony cushion-scale 
that threatened, at one time, to destroy the orange 
trees of California, and of that wonderful friend of 
the orange growers, the little Australian lady-bird. 
At the time of the great destruction caused by tliis 
scale insect, the United States Bureau of Entomology 
imported these lady-birds from Australia and dis¬ 
tributed them through the orange groves of Califor¬ 
nia, where they increased to such an extent and 
devoured such great numbers of the scales that the 
orange trees were saved, and to this day remain 
TOMATO WORM WITH PARASITES. Fig. 478. 
practically free from this pest. A second and greater 
triumph by this same lady-bird was accomplished 
when, at the request of Portuguese scientists, Dr. L. 
O. Howard sent colonies of the lady-birds in 1896 
to Portugal for the purpose of helping the orange 
growers there in their fight against this same cottony 
cushion-scale that had gained a hold in that country, 
and again threatened the destruction of the orange 
industry. In September of 1898 , the following report 
upon the work of the lady-birds during the two 
years they had been present came from Portugal: 
“Gardens and orchards that were completely infestec 
and nearly ruined are to-day entirely clean or well 
on the way toward becoming so.” Thus this wonder¬ 
ful little Australian lady-bird had again sustained its 
reputation as a firm and effective friend of the "or¬ 
ange grower. 
Again, in 1907, numbers of a certain tiny insect 
parasitic on the famous Hessian fly, were taken from 
the wheatfields of Pennsylvania and introduced into 
the wheatfields in the vicinity of Sharpsburg, Mary¬ 
land. In April, in these Maryland fields, not a single 
SKINS OF PARASITISED GREEN-BUGS. Fig. 479. 
maggot of the Hessian fly could be found with a 
parasite in it, but in July, after the introduction of 
the parasites from Pennsylvania, it was difficult to 
find many of the Hessian fly maggots that were not 
parasitised. In December of the same year, another 
examination showed that very few wheat plants were 
infested by the Hessian fly, and what maggots were 
present were nearly all parasitised. Regarding this 
experiment, Prof. Webster says “The evidence here 
is sufficient to show that this experiment had been 
entirely successful.” 
In the great fight against the Mexican cotton boll- 
weevil it has been found that many different kinds 
of native parasites are beginning to prey upon it, 
and experiments have been made to see if these 
parasites may not be taken from fields in which they 
arc abundant and introduced into localities where 
they are few. or none, with the hope that they may 
attack and destroy the boll-weevils in the latter 
fields. In a very careful experiment of this kind, 
Dr. Hunter says that the parasitism in one field at 
Dallas, Texas, was increased 9.1 per cent by the 
introduction of parasites obtained from a field near 
Waco, Texas, one hundred miles away. Thus we 
have careful and reliable evidence that, in some 
cases at least, this artificial introduction of "bug 
against bug” has been a success, and in two instances 
a most brilliant success. But how about the failures 
and the outlook for the future? 
At one time it was reported all over the country 
that a new disease had been found for the chinch, 
bug that would immediately exterminate this great 
pest. According to the reports, all one had to do 
COTTONY CUSHION SCALE ABOVE; AUSTRALIAN 
LADYBIRD AND LARVA BELOW. Fig. 480. 
was to scatter some of this fungus which had been 
grown on cornmeal mush or on other infested chinch 
bugs in a field where the bugs were abundant, and 
presto! the thing was done. Too much was said 
regarding this disease, too much was written about 
it, and too much was hoped for from its work. 
Farmers were misled into believing that a panacea 
had been found for this insect and would soon be 
found for all their other ills of injurious insects. In 
later investigations, it was found that certain condi¬ 
tions were absolutely essential for the growth of this 
chinch-bug fungus when it was scattered in a field 
among the bugs. Moreover, it was also discovered 
that this fungus was nearly if not always naturally 
present in every wheatfield, and when conditions were 
right it would usually develop of itself and destroy 
the bugs. Thus the advantages to be derived from 
distributing this disease are probably not as great 
as they were once thought to -be. At any rate very 
little of this fungus is now distributed and very little 
i-s said about it. 
Again, the work of controlling the so-called green- 
bug on wheat in Texas, Kansas, etc., by distributing 
its parasitic enemy among wheatfields during the 
season of 1907 gained considerable notoriety, and 
was much talked about by the newspapers. Tt did 
seem feasible and practicable to collect thousands of 
