13 



TOBACCO-WOBU. PAnASITE DESCRIBED. ITS WINGS. 



spot on the middle of eacli, tliat on the third segment being large, and as 

 the sutures contract in drying these spots become united. At its tip the 

 abdomen in the female is compressed and vertically truncated, with the 

 sting forming a conspicuous projecting point at the lower end of the trun- 

 cation. In the male the tip is rounded and without any projecting point, 

 though when living it miiy sometimes be seen to protrude two styles or 

 slender cylindrical processes pointed at their tips, and between these a 

 thicker process from the apex of which a fine bristle is occasionally thrust 

 out. The lags are bright tawny yellow, becoming more dull and pale in the 

 dried specimen. The hind feet and tips of the hind shanks are smoky or 

 blackish. The hind thighs arc also blackish at their tips, and frequently 

 show a dusky lino along their upper sides, extending nearly to the base. 

 The U'ings arc hyaline, glassy and iridescent. The forward pair have the 

 stigma appearing as a large, opake, triangular, brownish black spot on 

 their outer side slightly beyond tiie middle. The rib or marginal vein is thick 

 and brownish black, becoming paler brown towards its base. The basal 

 portion of the wing is traversed by two pale longitudinal veins, which 

 are parallel, the outer one straight, the inner one curved towards its 

 base. The outer vein sends otf a long and nearly straight branch obliquely 

 outward and backward to the anterior end of the stigma, tliis branch 

 bounding the discoidal and the first cubital cells on their fore sides. The 

 discoidal cell is triangular, with the vein on its inner side brown and angu- 

 larly bent at one-third and again at two-thirds of its length, giving off at 

 each of these angles a short obliciue veinlet, the first one of which is brown 

 and the other colorless. Tiie first cubital cell is of the same size with the 

 discoidal, and is irregularly six-sided, the anterior and the inner sides being 

 quite short; and the veinlet bounding this cell posteriorly is thick and 

 brownish black, the inner half of its length being oblique and the outer 

 half transverse, ending in the inner angle of the stigma. Beyond this, 

 traversing the apical tiiird of the wing are three longitudinal veins, which 

 are very slender and colorless. The middle one of these veins is abruptly 

 thickened and blackish brown for a very short distance at its base, this 

 thickened portion forming, with the oblique inner end of the veinlet last 

 described, two of tiie sides of the small triangular cellule which is common 

 in the wings of the insects of this genus and family, but the short veinlet 

 which should complete the enclosure of this cellule on its hind side, is 

 ■wholly wanting. 



Mr. Say is wholly silent respecting the interesting habits of this insect, 

 merely remarking that he obtained eighty-four of the flies from the larva 

 of a Sphinx in the month of June. As I have had the flies come from the 

 cocoons in July and also in September, it is probable that they arc abroad 

 upon Ihe wing during the wiiole summer season, actively' searching for 

 suitable worms to inoculate with their eggs. As will be seen from a state- 

 ment in one of the following pages, this parasite does not appear to be 

 limited to the tobacco-worm, but preys upon the larvro of other species of 

 Sphinx also. And some of our otiier species of Microgastcr have the same 

 habit of fastening their cocoons to the larvos from which they respectively 



