17 



which it raanag'ed to spread and to establish small colonies here and 

 there on various grasses, suited to its taste, which insured it a foothold 

 in this country and enabled it to multiply without being- detected in 

 time to adopt heroic measures for its extermination. The assumption 

 of its foreign origin seems the more reasonable since otherwise its 

 presence on small grain would have been observed from the earliest 

 time that these cereals were grown in this countr}'. 



After its introduction it has naturally migrated in various directions, 

 and established small, isolated colonies which have given it a chance 

 to obtain a foothold and to escape observation and detection. From 

 these centers of infection and with the assistance of air currents it 

 would be enabled to spread unobserved to far distant sections until it 

 reached grain-producing areas, the tender and succulent plants of 

 which are more suited to its taste. Thus it has multiplied rapidly and 

 spread from field to field and from State to State. Notwithstanding 

 that millions of the migrants are killed during this flight, enough remain 

 to stock new regions. 



At the time of migration, which in the Southern States, as far as 

 observed, takes place in May, most of the wheat and oats which 

 escaped injury had become so tall and vigorous as to withstand attack. 

 Possibly such growth ma^" be unfit for the sustenance of this plant 

 louse. 



Whether the species really thrives on corn or not is an open question. 

 Thus far it has never been received by this Department from an}^ of 

 the corn-growing sections. The writer is rather of the opinion that 

 the plant-louse frequentl}^ observed on corn is the common corn aphis, 

 Aphis viaidis Fitch, which somewhat resembles this grain louse both 

 in size and general coloration. 



What becomes of the survivors after leaving the grain remains an 

 unsolved problem. It seems, however, quite natural that during the 

 warmer season, after the harvesting of the grain, they will subsist 

 upon various succulent grasses growing in damp and moist localities, 

 such as the borders of rivers, creeks, swamps, or similar places, and 

 perhaps also on volunteer wheat and oats coming up in the fields. 

 These would afi'ord them a chance to survive and multiply until the 

 new grain makes its aj)pearance above ground. 



As with other aphides, a sexual generation will appear at the proper 

 time, and with it the eggs, for the preservation of the species. The 

 great majoritj" of our indigenous species of plant-lice produce the 

 sexual generation during the fall of the year, the eggs of which remain 

 dormant till the time at which a new cycle of plant life appears. A 

 few, however, produce the sexes and their eggs during the latter part 

 of spring or early summer, to hatch the following spring. What are 

 the habits of this grain aphis in this respect it is difiicult to say. 

 Taking into consideration the very early appearance of the lice in 

 3622— No. 38—04 2 



