June, '09] JOURNAL OP ECONOMIC ENTOMOLOGY 235 



WESTERN SPREAD OF THE COLORADO POTATO 



BEETLE 



(Leptinotarsa decemlineata) 



By J. M. Aldrich, Moscoic, Idaho 



Economic entomology has preserved in its archives pretty full de- 

 tails of the eastward advance of this insect. Starting from the arid 

 region along the east side of the Rocky Mountains in the late fifties, 

 when the introduction of the potato first enabled it to "switch" from 

 its wild food-plant, Solanum rostratum, it was about fifteen years in 

 reaching the Atlantic seacoast of the United States, and in a few 

 years more it was omnipresent in the eastern two thirds of the 

 country. 



It is a striking fact that the advance of settlement and potato- 

 raising west of the continental divide did not carry the beetle with it. 

 Professor Gillette writes me lately that even yet he has looked for the 

 insect in vain west of the main divide in Colorado. As far as I have 

 ascertained in considerable travel through the West, there are no 

 potato beetles on the western side of the Rockies except as noted 

 herein. 



Professor Cooley of the Montana Experiment Station writes me 

 that it has in quite recent years established itself in the Bitter Root 

 Valley of western IMontana, although as yet it has not reached the 

 upper end of the valley. He also finds it in Flathead County. Both 

 of these localities are on the western side of the continental divide. 



A new western record for the insect is the town of Nez Perce, Idaho, 

 about forty miles southeast of Lewiston. It has been established in 

 that neighborhood at least two years, and seems to have spread con- 

 siderably last summer. I do not know of it elsewhere in Idaho. 



Considering the numberless opportunities for the carriage of adults 

 westward on railroads, it seems probable that the species has gen- 

 erally died out when introduced, before it became fairly established. 

 I am informed on very good authority that a potato patch in Moscow, 

 Idaho, was infested about sixteen years ago, but the insect did not 

 reappear the following season. Our wet winters may account for 

 its inabihty to maintain itself here, but that certainly will not hold 

 good in all the territory concerned. 



It would be interesting to learn what others have observed in the 

 West, both in regard to the spread of the insect and to the agencies 

 which appear to retard its advance. 



