THE WESTERN" GRASS-STEM SAWFLY. 19 



Elymus condensatus, growing from plants that had been browsed by 

 cattle and had thrown up fresh green stalks. 



Mr. Norman Criddle states that in Canada the adults appear during 

 the second week in June and may be met with until about July 10. 

 Occasionally they may be found feeding on flowers. Doctor Fletcher 

 has taken them in Canada on flowers of the tumbling mustard. It 

 is unquestionably true that the time of their appearance and the 

 length of adult life are both largely governed by climatic influences 

 and vary with the season. 



When confined in emergence tubes or other limited places the males 

 develop savage instincts and attack each other without mercy, using 

 their jaws freely to snip off the antennae, and, in some cases, the legs 

 of their rivals. Singularly, very few of the females confined with 

 them are thus mutilated. 



OPPOSITION 



Weather conditions have always been an important factor in con- 

 trolling the oviposition of very many of the Hymenoptera, and they 

 are of particular importance in the case of the Cephus. These flies 

 go into hiding when the day is dark, damp, cool, or windy. Only on 

 bright, warm, still days are they to be found busy with the operation 

 of placing their eggs. In Utah, where the first studies of their habits 

 were made, the mornings and evenings are chilly as a rule, hence the 

 activity of these flies is confined to the hours near midday. They 

 are everywhere the most active between the hours of 10 a. m. and 

 2 p. m. 



The swaying of the grass and grain stems in the wind appears to 

 be a hindrance to them in alighting and ovipositing. A gentle breeze 

 will often keep them hovering for several minutes to the windward 

 of their goal, while a sudden mountain gust is apt to put an abrupt 

 end to all efforts for the balance of the day. Their actions are con- 

 trolled by unknown factors, for sometimes on a still, sunny day they 

 will spend much of the time roosting on the stems, while again, under 

 apparently the same conditions, they are constantly in motion, flying 

 and hovering a long time before alighting. 



While the female is poised in the air before a sod of grass or grain 

 she is evidently busy selecting the particular stem in which she hopes 

 to oviposit. Once she has chosen and settled, she seldom changes 

 to another stalk, although she may halt at several places on a single 

 stem and attempt oviposition at each pause. Occasionally, after a 

 hasty examination, she may again take to wing and make another 

 choice. Repeated observations seem to have established the fact 

 that one of the chief requisites of a proper stem is that it shall not yet 

 have put forth a head. In all the countless instances where ovipo- 

 sition has been observed, the female has never been known to choose 

 a stem with a head. 



