792 
ANNUAL REPORT OP NEW TORK 
TOBACCO-WORM. A DESTROYER OK TUI PARASITE DISCOVERED. 
On one occasion, when I was contemplating one of the tobacco-worms 
which I met with covered over with parasitic cocoons, I noticed a very 
email fly wandering about among the cocoons. My first thought was that 
this fly was probably one of the Microgaster parasites .which had just then 
come from some one of these cocoons ; but the query soon arose in my mind 
whether it might not be an enemy, stinging the cocoons to -destroy their 
inmates in the same manner they had destroyed the tobacco-worm. Its 
very small size did not enable the eye to discover whether it really was 
one of the Microgaster flies. I was so fortunate as to succeed in enclosing 
it in a small vial, and then upon examining it with a magnifier, I became 
assured it had not come from the cocoons, for I perceived it pertained to a 
different group of parasites from that to which the Microgaster genus 
belongs. But how could the highly interesting and important point be 
ascertained, whether it actually was a destroyer of the inmates of these 
cocoons ? With the hope of obtaining further light upon this subject a 
portion of the stalk of the plant with the tobacco-worm adhering to it 
was cut off and enclosed in a glass jar. On the fifth day thereafter, two 
Microgaster flies made their appearance in the jar, and the worm now 
being dead and beginning to become putrid, the cocoons were all removed 
from its surface and enclosed in a vial. It was feared that this slight vio¬ 
lence to them had destroyed their inmates, as day after day now elapsed 
and no more flies came from them. But, three months later, in December, 
they being kept in a warm room, a dozen flies wore discovered, wandering 
around in this vial ; and for some weeks after, others continued to come 
forth from the cocoons. And these proved to be identical with the single 
fly which had been captured among these cocoons so long a time before- 
It was therefore evident that that fly was the parent of these which were 
now issuing from the cocoons ; and so industrious had that little creature 
been, that it had punctured and dropped one of its eggs into all save two 
of the cocoons, which were more than a hundred in number; and these 
two, it is probable, would not have escaped, if the fly had not been inter¬ 
rupted and taken away from its work. 
These destroyers of the insect which destroys the tobacco-worm are very 
small four-winged flics of a shining dark green color, with pale yellowish 
legs and white feet. They belong to the order Hymenoptf.ra and the family 
ChalcididjE, and are closely related to the Hessian fly parasite, Semiotel- 
lus destructor, figured in my Seventh Report, plate 3, fig. 1, which figure 
will also serve to represent this insect in almost every particular. It per¬ 
tains to the genus Pleromalus, a name derived from two Greek words, 
meaning bad wings, the wings in these insects being nearly destitute of 
ribs or veins. As they, by destroying the parasite of the tobacco-worm, 
cause that worm to be more numerous and hereby more injurious to the 
tobacco, and as they will often occur lurking about this plant in search of the 
cocoons upon which to bestow their eggs, they may not inappropriately 
be named the Tobacco Pteromalus. All the flies which came from tho 
cocoons were females, from which the following description is drawn. 
The Tobacco Pteromalus {Pleromalus Tabacum), is one-tenth of an inch 
