121 
It will be noticed by referrino- to the table that the greater percent- 
aiie of parasites come from the smaller larvae; or, in other words, that 
the larvfe are destroyed before the}^ are half grown and consequently 
before they have done the greater part of their injury to the plants. 
HYMENOPTEBOUS PARASITES. 
Practically all the parasites bred from the young larvae belong to 
th(^ same species^ JficropI it is n ig7'ij)en7his Ashm.^ of the family Bra- 
conidje. This species was first bred in the laboratory from a larva 
collected on tobacco at Paris July 5, 1904, but it was not observed in 
any numbers until the middle of August, when a large percentage of 
the boUworms feeding on alfalfa were found to be parasitized b}^ it. 
Its frequent occurrence on cotton after that time has been referred to. 
The eggs of the parasite are deposited in larvae which are about 
10 or 12 mm. in length, or much more rarely in larger specimens. 
After it has been stung by the Braconid, the larva continues to feed, 
but at a much diminished 
rate, for two or three days. 
It now becomes very slug- 
gish and eats the involucre 
of the square or boll in''>^ 
rather desultory manner,^, 
chewing it into small bits, 
many of which it fails to 
swallow. These small pieces 
usually remain webbed to- 
gether loosely by delicate 
strands of silk spun by the 
boll worm, and present quite 
a characteristic appearance. By the time the parasitic grub is full- 
grown, the larva lias ceased feeding entirely and is scarcely larger 
than when first attacked. The Microplitis now bores its way out 
through the skin of the quiescent bollworm, leaving a large black scar 
(see PI. XIX, fig. 1) to mark the point of its emergence, which is gen- 
erally on one side of the bod}^, near the first pair of prolegs. In one 
case the grub was watched during the act of emerging from the boll- 
worm. It had protruded the pointed head and was gradually working 
its fleshy body through the small hole in the larva's skin. In doing this 
the body had to be constricted dumb-bell shape in order to pass through 
the small orifice. Once free from the larva, it spins its pupal cocoon 
(see PI. XIX, fig. 1, and text fig. 23) on some surrounding object, gen- 
erally a stem or a leaf, spending several hours in this work. The cocoon 
is about 5 or 6 mm. in length, oval in shape, pale dingy yellow in color, 
and furnished with a few coarse longitudinal ribs. When first spun it 
is almost white and rather delicate. After a few hours, however, it 
acquires its mature color and its consistency becomes verj" tough. 
LLH 
Fig. 23.- 
Micropliti^ nigripennis: adult, larva, and 
cocoon (original). 
