12 MONTANA EXPERIMENT STATION BULLETIN 484 



selshell, Yellowstone, Big Horn, Treasure, Rosebud, Powder 

 River, Custer, and Prairie counties are now known to be infested 

 with economic populations of alfalfa weevils. During the past two 

 years, this pest has consistently caused more damage to alfalfa 

 than any other insect. During the biennium, the alfalfa weevil 

 has been one of the more important economic insect pests to Mon- 

 tana agriculture. The early spring chlordane treatment recom- 

 mended in 1951 was effective where used properly, but its use 

 was limited due to the relatively high cost per acre for treatment. 

 During the fall of 1951 a 20-minute, 16 mm. color sound motion 

 picture entitled "Alfalfa Weevil Control" was prepared by this 

 office in cooperation with the Agricultural Experiment Station 

 at Montana State College. In 1952, the film was used by this of- 

 fice at 22 alfalfa weevil control meetings which were attended by 

 1,258 people. In addition, it had 9 other showings to a total at- 

 tendance of 809 people. This educational effort along with the 

 lower cost of dieldrin application resulted in a large percentage 

 of the infested acreage being treated with dieldrin in the early 

 spring of 1952. 



In general, the alfalfa weevil infestation and damage appear- 

 ed to be moderate in 1951. In 1952 consistently higher populations 

 and more than average damage was noted. For the first time in 

 1952 it was evident that extremely high populations of adults 

 caused damage to the alfalfa largely through their egg-laying ac- 

 tivities. The newly recommended early spring dieldrin treatment 

 was very successful, and it has resulted in large returns in terms 

 of alfalfa production at a relatively low cost of treatment per 

 acre. 



LYGUS BUGS (Lygus sp.) 

 All alfalfa seed areas observed in 1951 had economic infes- 

 tations of Lygus bugs during mid and late summer. The same was 

 true in 1952 except that Lygus populations in southeastern Mon- 

 tana appeared to be unusually high. Most alfalfa seed growers are 

 now using DDT and toxaphene spray treatments for the control 

 of this sucking insect pest. 



SWEETCLOVER WEEVIL (Sitona cijlindricollis) 

 Scattered moderate to heavy infestations of sweet clover 

 weevils occurred over many areas of the state in 1951 with a few 

 cases of marginal damage to alfalfa being reported. In the spring 

 of 1952, severe defoliation by adult sweetclover weevils was evi- 

 dent in nearly all parts of the state; again a few cases of marginal 

 damage to alfalfa occurred. 



CLOVER APHID (Anuraphis bakeri) 

 Economic populations of clover aphids were present in most 



