500 Journal of Agricultural Research voi.v. no. 12 



The mouth, pharynx, esophagus, and stomach have approximately the 

 same form and relative positions as in the first instar. Owing to the 

 fact that the blood of the host is green, the stomach content of the 

 parasite at first takes on a greenish brown color which finally becomes 

 a deep green, similar to the blood of the host, and later, at the end of the 

 stage, this again becomes greenish brown. 



During the last two days of this stage the anal opening, the diameter of 

 which nearly equals that of the body, slowly contracts, and violent con- 

 tractions of the longitudinal muscles of the stomach, which cause it to 

 shorten, slowly draw the caudal vesicle in through the contracting anal 

 opening. The Malpighian vessels are also drawn in by the contraction 

 of the stomach and are now two-thirds as long as the larva. After the 

 caudal vesicle has been drawn completely within the body, the anal 

 opening contracts still further, and the anus is formed. 



The tenidia of the tracheal system can be seen forming soon after the 

 first molt. Those of the two main longitudinals and their anterior con- 

 necting branches are first visible, and there are 1 1 branching centers on 

 each longitudinal from which arise branches sending tracheae to all parts 

 of the body, some even extending posteriorly into the caudal vesicle 

 along the lateral walls and the stomach. Nine pairs of short, stublike 

 branches are noticeable in the older larvae, arising near the bases of the 

 anterior nine pairs of dorsal branches of the main longitudinals. In the 

 still older larvae, those nearly ready to emerge, eight pairs of spiracles can 

 be seen forming at the surface of the body, and these are connected with 

 the first, and the third to ninth, inclusive, pairs of stublike branches 

 previously mentioned, by tracheae destitute of air. These become filled 

 with air when the larva molts at emergence and the spiracles are un- 

 covered and function. The spiracles that connect with the second pair 

 of stublike branches do not form during this stage. 



After the caudal vesicle has been drawn in, the larva is ready to emerge 

 from its host. The mandibles of the third instar, which are now devel- 

 oped and protrude, slowly cut and tear through the muscles and skin of 

 the host as the larva presses its head against the body walls of the cater- 

 pillar and moves them backward and forward. When a slit has been 

 made of sufficient size the larva squeezes through the opening, molting 

 the previously loosened skin as it emerges. During this process the 

 caterpillar lies quietly as though paralyzed. About the time the parasites 

 have nearly finished their cocoons, it usually revives enough to crawl 

 away. 



Third instar (PI. L, fig. 7). — The third instar lasts from the emer- 

 gence from the host until pupation, the time being approximately 2K 

 days. 



The newly emerged larva is light green in color. It is covered with 

 minute spines, with a number of short black spines somewhat irregularly 



