230 



EXPERIMENTAL FARMS. 



There is, however, a marked difference in the season of the Manitoban sp>ecimens 

 and that of those studied by Prof. Oomstock at Ithaca, N.Y., which were in general 

 terms just about one month earher. By the 19th of July, 1889, all the larvae examined 

 at Ithaca had descended to the lowest joint, while in Manitoba this year, nearly a month 

 later in the season, some of the larvae were not full-grown until about the 13th of August. 

 Specimens of the mature insect were flying at Indian Head on the 5th of July, 1895, and 

 it would take from a month to six weeks before the larvae from eggs laid by these reached 

 full growth, which would occur about the same time as the ripening of the wheat, when 

 naturally the straws would dry up and become unfit for food. 



Several European writers have treated of this insect and its habits. Probably the 

 best known account is that of John Curtis in his celebrated work Farm Insects (1860). 

 This account includes the observations of Herpin and other French authors. The most 

 complete study of the insect is that by Prof. Comstock presented in the bulletin above 

 referred to. 



A summary of the life history of the Wheat-stem Saw-fly is as follows : — 

 The eggs are laid inside the wheat stem just before the ears appear above the sheath, 

 being inserted into the hollow of the stem through a minute hole cut by the female with 

 its saw-like ovipositor. The egg hatches in a few days, and the young larva grows 

 rapidly and attains full growth before the straw ripens and hardens, by which time it 

 will have eaten its way from the topmost joint of the stem to the lowest, feeding chiefly 

 on the substance of the knots, but also on the inside tissues 

 of the straw. About the time the grain ripens, it descends to the 

 bottom joint, and, just above the surface of the ground, gnaws 

 away the inside substance oi the straw so as to cut a ring 

 almost, but not quite, through to the outside. (Fig. 2.) This is to 

 enable the perfect fly to emerge easily in spring. It then 

 spins a thin, delicate cocoon ; and, like the larvae of most saw- 

 flies, remains torpid until the following;' spring, when it turns to a 

 pupa only a few days before transforming into the perfect fly. The 

 date of appearance of the perfect insect evidently varies with the 

 season and locality. The adult is a shining black four-winged fly, 

 banded and spotted with yellow, with the abdomen slightly com- 

 pressed. The head is large, with prominent eyes, and there are also 

 three ocelli or minute simple eyes near the summit of the head. The 

 antennae are slightly club-shaped and composed of about twenty 

 segments. The female is rather larger than the male and less orna- 

 mented with yellow. The average length is about one-third of an 

 _g ^ inch (male, 8 mm.; female, 10 mm.). This insect is interesting 



mfested by Wheat scientifically, as it must be classified between the true Saw-flies , 

 Saw-fly: a, cocoon; (Tenthredinidce) and the Horn-tails {Uroceridce), so-called from the 

 c' llvcni cut'"^^' ^^^^ ^^^^ ^^® \iiTW3s bear a sharp horn-like appendage at the end of 

 scattered borings, tihe body. 



(Figure kindly lent It, is evident from an examination of the different stages, that it 



stockO ^^ "^0^^ nearly related to the Horn-tails. The Wheat-stem Saw-fly is 



a native of most of the countries of Europe, and in' some years, par- 

 ticularly in France, it has been the cause of much loss. Miss Eleanor A. Ormerod 

 speaks of it in many of her invaluable reports, and shows that while it occurs in notice- 

 able numbers every year, it is only occasionally a serious enemy to the wheat grower. 



The question of the introduction of this European insect into America is one of 

 some interest to entomologists, and it seems difficult to und-^rstand how it could have 

 taken place. It has been suggested, however, by Prof. Comstock, who found a few 

 cocoons in the straw above tlie point where it would have been cut by a reaper, that "a 

 small proportion of the insects are probably removed from the wheat fields in the straw 

 and, consequently, there is danger of the spreading of the species in this way. It is pro- 

 bable that the insect was introduced into this country in straw used in packing, and it 

 may be further distributed here in the same way." {Bidl. No. 11, p. 141). 



