350 



ECONOMIC ENTOMOLOGY 



probably with species of Agropyron as its host plants. A serious 

 pest in the West on wheat and rye (Figs. 232 and 233). 



Adult. — A shiny black 4-winged fly, 3"^ inch long; abdomen with 

 three prominent yellow rings; legs yellow. Female with a short 

 stout horn-like ovipositor. It rests head downward on the stems of 

 grasses, with its wings very close together over the body. June 10- 

 July 10. 



Eggs. — Minute, white, cylindrical. 



Larva. — Dull yellowish-white, }yi-}^'2 inch long; first two segments 

 swollen; end of abdomen with a short blunt projection. Always 

 occurs within the stem. Bores downward in the stem, reaching base 



Fig. 233. — Full grown larva of the western wheat-stem saw-fly (Cephus occidentalis) 

 (After Criddle, Bui. 11, Ent. Br. Can.) 



about August ist and cutting the stems through level with ground; 

 remains all winter in stub until following May. 



Pupa. — Formed in May in stub inhabited by larva. 



Control. — I. Plough infested stubble 5 inches deep in fall, with 

 attention at least to worst infested fields. 



2. All infested grasses', such as western rye grass, timothy and the 

 prairie grasses next to growing crops should be cut between July loth 

 and August ist. 



SiRiciD^ (Horn-tails) 



Pigeon Tremex (Tremex columba Linn.). — Injures elm and maple. 



Adult. — Female a large 4-winged fly, 2 inches long, with a prominent 

 yellow horn at end of abdomen; head and thorax reddish-black, ab- 

 domen cylindrical, dark brown, with seven yellowish band-like mark- 

 ings; male smaller, without horn. June-August (Fig. 234). 



Eggs. — Oblong oval, jointed at ends, V20 inch long. 



Larva. — ^Large, soft, yellowish, cylindrical, with six true legs and 

 a horny point at end of abdomen; boring into wood. Parasitized by 



