TWENTY-FIFTH REPORT OF STATE ENTOMOLOGIST 3S 



111 lf)3;i tliere were tliirteen sueli stations, and in 1934, twenty-seven 

 stations, practically all in the eastern part of the state, showed rain- 

 fail below this amount. Only three stations, Canyon Ferry, East 

 Helena, and Ballantine, reported less than four inches of rainfall 

 during May, June, and July, for hoth W'.V.i and 19:54. An increase 

 in pale western cutworm damage may occur in the vicinity of (Masoil 

 (southeastern Lewis and ("lark County), in the dry-land sections near 

 Ballantine, and to some extent in eastern and northeastern ^Montana 

 in 1935. 



INSECT PESTS OF FIELD CROPS 



The Sugar-Beet Leafhopper {Eutettix tenellus Baker) 



In 1934 the disease known as curly toi) of sugar beets appeared 

 in Montana for what is believed to be the first time in the history of 

 our beet growing sections. The carrier and disperser of this disease 

 is the beet leafhopper. This insect normally breeds in the foothills 

 of arid regions and then migrates to the valleys and sugar beet fields 

 during the early part of the growing season. The disease it carries 

 to the beets is poorly understood at the present time but in many 

 years is responsible for damage estimated in millions of dollars in 

 other Western States. 



From Laurel to Worden during the ])ast summer fields of beets 

 were found where two to ten per cent of the beets were affected by 

 the disease. In the Bitter Root Valley less than one per cent of dis- 

 eased beets occurred. None could be found in the Milk River Valley. 

 In spite of the prevalence of curly top in part of the Yellowstone 

 Valley and the fact that the disease never occurs without an invasion 

 of leafhoppers, very few of these insects could be collected in the 

 beet fields. It is believed that the few insects present at the time the 

 disease was discovered could not have been responsible for the rather 

 extensive infection wdiich obtained. 



It has been pointed out at various times in these reports that 

 with shifting climatic conditions in Montana we may expect invasions 

 of southern insects or temporary increases in the normal abundance 

 of local species. During periods of mild weather they increase rap- 

 idly to such an abundance that they are suddenly of great economic 

 importance. However, after the intervention of one or two severe 

 winters or a season of high precipitation, they decline to their normal 

 insignificance. This will probably be the case with the sugar-beet 

 leafhopper. 



