THIRTIETH REPORT OF THE STATE ENTOMOLOGIST 5 



correlation between these areas of infestation and the migratory 

 phases of M. mexicanus. This is indicated by the fact that in the 

 Triangle area where the migration was halted by the mountains, 

 the predominant species in many fields was Melanoplus bivittatus 

 rather than M. mexicanus. As reported in the Twenty-ninth Re- 

 port of the State Entomologist 2 there was a marked decrease in 

 grasshopper populations from 1939 to 1942. This condition carried 

 over into 1943 with general grasshopper populations the lowest in 

 many years. Even with these conditions, however, enough 'hoppers 

 remained in many parts of the State to present a serious threat to 

 the greatly increased food-production goals. 



The area influenced by the great migration of 1938 was limit- 

 ed on its western border by the Rocky Mountains and the above 

 remarks apply only to counties lying east of the Continental 

 Divide. In the intermountain counties lying west of the Divide a 

 trend almost exactly opposite to that recorded above began to de- 

 velop. Scattered noneconomic infestations began to increase in 

 numbers and by 1942 Sanders, Lake and Missoula counties report- 

 ed threatening 'hopper populations. Other counties probably ex- 

 perienced similar increases but, with the exception of Flathead 

 County, none of the other counties maintained County Agents, 

 and grasshopper adult or egg surveys were not conducted in these 

 counties. 



1943 Season 



Grasshopper egg surveys in the fall of 1942 indicated that in 

 1943, outbreaks were likely to occur in the Yellowstone River 

 drainage, the western portion of the Triangle area, and in Lake 

 and Sanders counties. Greatest egg concentrations were found in 

 the Upper Yellowstone River Valley and its tributary, the Big 

 Horn River. (Figure 1.) 



Eggs were first reported hatching in the area around Billings 

 on April 23. Subsequent cold weather during which temperatures 

 of 24°F. on May 9 and 32°F. on June 3 were recorded retarded fur- 

 ther hatching. Because of the delayed hatch the cold weather had 

 little effect as a control factor. Hatching increased after June 6, 

 but the continued cold prolonged the hatching period until the 

 latter part of July. First adults were reported July 1. As a conse- 

 quence of the irregular development all stages in development 

 were to be found in the same area at the same time. In some in- 

 stances new adults were laying eggs before all eggs of the pre- 

 vious season had hatched. 



Egg predation was of considerable importance in reducing 

 'hopper populations. In some areas blister beetles destroyed as 



"Mont Agr. Exp. Sta. Bull. 408, pp. 4-10. 



