2 BULLETI]Sr 808, U. S. DEPARTMENT OF AGRICULTURE. 



running into the millions of dollars every year. Despite this fact 

 very little has been known concerning the identity and habits of the 

 species which cause these losses. For example, it was not known 

 definitely whether HarmoUta tritici Fitch, the most important mem- 

 ber of the genus, had a dozen host plants or whether it was confined 

 to, wheat alone. The object of this paper, therefore, is to placa on 

 record in as brief a manner as possible the main facts, in so far as 

 they have been developed, in the life histories of the species that 

 have been studied thus far, and to propose a basis for control. 



The species infesting the grain crops will be considered first, then 

 those affecting the cultivated grasses, and lastly the species living in 

 wild grasses. Nearly every species is of either direct or indirect 

 economic importance. Those affecting the grain crops and the culti- 

 vated grasses are obviously of direct economic importance because 

 of the very considerable losses entailed by their depredations or their 

 potential capacity for injury. The importance of the different 

 species varies greatly since the damage inflicted by some is far 

 greater than that caused by others. The economic aspect of those 

 species affecting wild grasses is less obvious. They do not cause a 

 loss to the farmer, but on the contrary' probably are an advantage to 

 him, since they serve as intermediate hosts for the many parasitic in- 

 sects which play such an important role in the natural control of the 

 species infesting cultivated crops. Without these intermediate hosts 

 it is doubtful whether some of the parasites would be able to main- 

 tain themselves under the abnormal conditions created by cultiva- 

 tion. The more important species of parasites are common to the 

 majority of species of Harmolita, however, and consequently are able 

 to survive, those periods during which there is a lack of hosts breed- 

 ing in cultivated crops, by turning their attention to related species 

 breeding in wild grasses. 



It is difficult to estimate the value of jointworm parasites in terms 

 of dollars and cents to the wheat-growing regions east of the Mis- 

 sissippi Eiver. The writer is convinced, however, that farmers would 

 have been obliged to resort to artificial measures of control for the 

 wheat jointworm years ago had it not been for the efficiency of these 

 parasites. The parasites of the jointworms will be treated in a paper 

 to be published subsequently. 



SPECIES INFESTING THE GRAIN CROPS. 



THE WHEAT JOINTWORM.^ 



HarTYidlita tritici probably is the most important species in the 

 whole genus, since it causes very serious losses in nearly all the wheat- 

 producing States east of the Mississippi River and in a large part of 



1 HarmoUta tritici Fitch., 



