16 MONTANA EXPERIMENT STATION BULLETIN 425 



heavier population, and injury was noted in the additional coun- 

 ties of Dawson, Wibaux and Fallon. (Figure 4) . 



The biology and control of this insect has been detailed else- 

 where" and will not be repeated here. This was without doubt the 

 insect most injurious to wheat in the State in 1944, overshadowing 

 the injury sustained from grasshopper attacks. Spring wheat was 

 most highly infested, some infestations approaching 100 percent. 

 Observations made during July of 1944 in heavily infested areas 

 indicated that barley was consistently infested, in the common 

 varieties grown in the State, to the extent of about 10 percent, 

 even in areas where adjacent spring wheat carried from six to 

 seven times this infestation. The percent survival in barley, how- 

 ever, has not been ascertained. It would seem that, even though 

 barley may not be an immune crop, it suffers much less injury 

 than wheat as far as common varieties in Montana are concerned. 

 Several specimens of flax infested with the wheat stem saw- 

 fly have been examined. Where these insects are abundant, this 

 attack seems not uncommon. It has been previously noted in in- 

 fested Canadian areas and has been discussed by Farstad' who 

 has made some detailed observations on its behavior in this crop. 

 As a result of these studies, in which he found that the larvae did 

 not survive in flax, Farstad states: 



"As a potential pest of flax, Cephus cinctus Nort. appears to 

 be of little importance. A relatively insignificant number of 

 branches may be severed, and in combination with grasshopper 

 feeding some breakage may occur. The value of flax as a crop for 

 ridding a field of its sawfly infestation probably far outweighs the 

 small economic loss that can be directly or indirectly attributed to 

 this insect". 



A possible addition to the complications involved in the con- 

 trol of the wheat stem sawfly presented itself during the summer 

 of 1944. It has previously been considered that this insect had one 

 generation annually. On July 18th, an untouched stubble field in- 

 fested in 1943 (south of Ethridge in Toole County) was examined 

 by P. D. McElliott and R. G. Newell. At this time, when the over- 

 wintering larvae should have pupated and emerged, approximate- 

 ly 50 percent of the infested stubs contained full grown, living and 

 active larvae. Normal pupation and emergence had apparently 

 taken place in the remainder of the infested stubble. On the basis 

 of this observation, there may be a possibility that under certain 

 conditions a population may go through two seasons before emerg- 

 ing as adults. There is insufficient information on this point at the 

 present time to draw any conclusions, but the possibility cannot 

 be overlooked. 



3 War circular 6, Mont. Agr. Exp. Sta. January, 1944. 



♦Wheat stem sawfly in flax. Scientific Agriculture, 24:8, pp. 383-386, April. 1944. 



