2 MISC. PUBLICATION 17 4, U.S. DEPT. OF AGRICULTURE 



INTRODUCTION 



The hessian fly, Phytophaga destructor (Say), has long been 

 known as the major pest of the wheat plant in the United States, 

 and it is similarly injurious to this crop in Europe as well as in 

 various other parts of the world. First discovered in North Amer- 

 ica more than 165 years ago, it has spread from the original point 

 of discovery in the neighborhood of New York City over most of 

 the wheat-growing region of the United States and Canada and 

 for many years has been the object of almost constant investigation. 



Because of the important influence which they exercise in its con- 

 trol, the hymenopterous parasites of this pest early became a matter 

 of interest to entomologists and have become increasingly so as the 

 years have gone by. Because of aroused interest in natural-control 

 methods, the past 2 or 3 decades have witnessed extensive and in- 

 tensive studies on the biology of various hymenopterous parasites of 

 injurious insects. Workers on the hessian fly have been active in 

 this field, their investigations resulting in the uncovering of numer- 

 ous heretofore unknown parasites attacking the fly and in the ac- 

 cumulation of much information regarding those already known. 

 More than 130 authors and upward of 200 separate articles involv- 

 ing seven different languages make up the present literature dealing 

 with parasites of this one host. This mass of literature, scattered 

 through many different journals, bulletins, etc., and involving much 

 synonymy and many changes in names, taken in conjunction with 

 the natural difficulties involved in the identification of these minute 

 insects, has made it extremely difficult for one engaged in a study 

 of the parasites of the fly either to determine their identities or to 

 know what has been written about any particular species. A press- 

 ing demand has arisen for a coordinated discussion of information 

 now available regarding the exact identities, synonymy, distribution, 

 etc., of the various species attacking this fly. 



The object of this publication is to bring together, in so far as 

 possible, in the case of each species attacking the fly, a complete bib- 

 liography and review of the literature, a description that will make 

 it possible to recognize the species, a list of its synonyms, and a short 

 outline of what is known regarding its hosts, life history, and dis- 

 tribution. 



GENERAL HISTORY 



The first record of a hymenopterous parasite of the hessian fly was 

 made by Thomas Say in 1817, when he named and described the 

 species now known as Merisus destructor (Sa}^), giving a short 

 account of its oviposition and development. Ajiother early investi- 

 gator, E. C. Herrick, in 1842 recorded the rearing of five species from 

 the fly. One of these he identified as the species described by Say, 

 but the others were left unnamed. Herrick gave the first account 

 of a parasite ovipositing in the egg of its host and developing upon 

 the larva. The species is now believed to have been Platygaster 

 hiemalis Forbes, which did not receive a name until over 40 years 

 after Herrick's observations were published. As will be shown else- 

 where, this interesting observation by Herrick was discredited by 

 many subsequent writers but is now known to have been entirely 

 accurate. 



