542 REPORT OF THE COMMISSIONER OP AGRICTJLTURE. 



began to issue in numbers from Virginia straws December 10. De- 

 cember 31 another large lot issued, as also on January 5, January 8, 

 and February 1. 



From our breedings it becomes doubtful wbetber tbe principal 

 parasite of the Joint Worm {Semiotellus chalcidiphagus, Walsh) 

 has one or two annual generations. A few specimens were swept in 

 the field by Messrs. Pergande and Stewart as early as June 13, while 

 in til- Department breeding-jars they issued in large numbers through 

 July and on until August 22. Then no more were noticed until (Jc- 

 tober 10, when a number were found in the jars.* During the winter 

 straws cut open showed the presence of many of these parasites still 

 in the larval state. April 9 a large number issued, and none after 

 this date. 



From these facts it seems that this species winters both in the adult 

 state and as larvae in the straws, the latter issuing in early spring. 

 They undoubtedly oviposit in growing grain infested with Isosoma 

 in the spring, and some individuals develop and issue in July and 

 August, while others winter in the straw and stubble as larvse. What 

 becomes of the adults which issue so early in the season we can only 

 surmise. It is after harvest when they appear, and to parasitize 

 Joint Worm larvae they would have to pierce the hard stubble or 

 work their way into their own holes of exit or into the cut ends of 

 the stubble; not a very likely proceeding. These early individuals 

 may oviposit in some other host, or they may live and hibernate 

 without ovipositing before spring. 



The common Eupelmus allynii (French) is also, as we have else- 

 where stated, f a parasite of Isosoma hordei. as well as of Isosoma 

 tritici and the Hessian Fly (Cecidomyia destructor). From the 

 Joint Worm it has also been bred from Virginia specimens, and on 

 three dates, viz, August 32, 1884, October 11, 1884, and April 9, 1885. 

 Although a considerable number issued on each of these dates, it 

 appears to be only about one-tenth as numerous as the Semiotellus. 



THE WHEAT-STRAW ISOSOMA. 

 {Isosoma tritici, X Riley.) 



In our annual report for 1884, in describing the larger Wheat-straw 

 Isosoma, we called attention (p. 358) to the possible relationship be- 

 tween this species and /. tritici in the following words: 



"It may be here stated as an interesting fact that of the specimens 

 so far reared both of tritici and grande, all are females, and whether 

 or not there is any dimorphic relationship between these two forms 

 is a question which future observations alone can decide. The prob- 

 abilities are, however, that there is no connection between them, for, 



* There is a possibility that some of these issued several days prior to this date. 



f On the Parasites of the Hessian Flv, by C. V. Riley, Ph. D., Proceedings of the 

 U. S. National Museum, 1885, pp. 413-432. 



X As the oVjject of this article is to show that tlie t'wo species whicli Tve have de- 

 scribed as Isosoma tritici and I. grande are in reality but seasonal dimorphic forms 

 of one and the same species, it may be well to state that we retain the species name 

 "tritici'' as having priority, and because it represents the bisexual form of the 

 species. We retain tliis name in preference to *' gi'cincle" because, in addition to 

 these reasons, it is an eminently appropriate name, and, as we have previously 

 shown, Fitc-h's Euryfoma tritici is but a variety of Isosoma hordei, and cannot even 

 be looked upon as entitled to a varietal name, since there is no constancy in the 

 characters upon which it is based. 



