17 



TOBACCO-WOBU- PAKASITB AND ITS DESTROYEn. THEIB DIFFZREMT MOTIONS. 



dinal vein is perceptible, wliicli, near its middle, gives off a branch running 

 almost to the inner hind end of the wing. The iiind wings arc much 

 smaller and without veins, except a brown subcostal one, which extends 

 into the outer margin and abruptly ends a little bcj'ond tlie middle. 



All the examples of this species, which I have obtained from cocoons upon 

 the Tobacco-worm, have been females. The last of August, 1862, I received 

 from Dr. Allen of Saratoga Springs, a larva of the Sphinx Kaimice to which 

 thirty-six cocoons were adhering. And the middle of July, the following 

 year, H. Markham, Esq., of Stony Brook, Long Island, sent me the same 

 larva, similarly infested. It may here be incidently observed that both 

 these gentlemen met with these larvaj upon the leaves of the grape-vine. 

 As I have repeatedly observed it, in different years, upon the lilac, the 

 leaves of which are certainly its usual food, the interesting query arises, 

 whether, when it is infested internally with parasites, they do not cause a 

 morbid appetite in the worm, whereby it ceases to relish its natural 

 food and comes to crave the leaves of the grape in place of those 

 of the lilac ? Plies were obtained from more than half the cocoons 

 upon the first mentioned worm, and these being all of one species, I 

 supposed they were probably the true parasites of the Lilac-worm. But 

 I now find on comparing them, that they are identical with this species 

 which is now under consideration. It thus appears that the cocoons ad- 

 hering to the Lilac-worm had been formed hy a species of Microgaster, 

 probably' this same species which infests the Tobacco-worm, aTid that the 

 flies I obtained were its parasites and consequently were protectors instead 

 of destroyers of the Lilac-worm. The cocoons from Mr. Markham, might 

 perhaps have given more light upon this subject, and I now regret that, when 

 they came to hand, supposing they would only produce the same flies which 

 I had examined the preceding summer, I felt that it would be a waste of 

 time to attend to the rearing of their inmates. 



Of the flies obtained from the Lilac-worm, four were males, whereby it 

 appears that this sex diflers from the females above described, in the fol- 

 lowing particulars: 1st, their color is lighter and more bright, being bril- 

 liant metallic green, when dried becoming blue green; 2d, their antennsB 

 are tarnished yellow, longer, and not at all thickened toward the tips 

 their joints being cylindric and a third longer than thick, with the last 

 joint egg-shaped and but little longer than its predecessor; 3d, the abdo- 

 men is flattened oval and rounding at its tip, with a large translucent pale 

 yellow spot near the base; 4th, the legs are paler and pure yellow without 

 any mixture of orange or tawny. 



One who is acquainted with this insect and the Microgaster fly, will 

 readily distinguish them by their motions, notwithstanding their sniallness 

 and similarity in size. The Microgaster is very brisk and active in its 

 movements, running about with agility and flying away if an}' danger 

 menaces it. This insect on the other hand, appears tame and sedate, walk- 

 ing around slowly, and as if with deliberation as to what it is doing; and 

 if any annoyance approaches it, to escape therefrom it gives a slight skip, 

 throwing itself about an inch, and repeating this leap again and again if 

 pursued, it being not at all inclined to take wing. 

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