PRELIMINARY REPORT ON ALFALFA WEEVIL. 25 



MIGRATION AND DIFFUSION. 



There are two periods during which the adult insects migrate, more 

 or less aided by the winds and perhaps to a less extent by other 

 agencies. Such as have not hibernated directly in the alfalfa fields 

 become active in early spring and fly about freely, seeking 

 such fields in which to deposit their eggs. This spring migration 

 covers a considerable period of time — about six weeks, as estimated 

 by Mr. Titus. As the females are more or less heavily lad'en with 

 eggs, however, the flight of the individual is perceptibly shorter than 

 in the second, or summer, migration, the season for which begins 

 early in June and continues for three or four weeks. Another reason 

 for the shorter flight in spring is that the beetles are searching about, 

 not for places of hibernation, but for breeding places. Having found 

 these, they naturally would not go farther unless carried by the 

 winds. In case of a summer flight, however, the conditions are 

 altogether different. This is the season during which most nomadic 

 insects become more widely diffused. At this time the beetles fly 

 high in the air and apparently over long distances. They are also 

 to be observed crawling about in almost every situation, as with the 

 larger species, Hypera punctata, which may be observed wandering 

 aimlessly over the pavements in the midst of large cities. Then, 

 too, they appear to float about freely on the surface of water, and 

 are doubtless carried long distances down stream by the current. 

 We know this is true in the case of irrigating ditches and canals, and 

 it is also true of the larger species just mentioned in case of streams 

 in the East. This habit of the beetles in hiding themselves away in 

 any crevice or aperture that will accommodate them doubtless has 

 considerable to do with their diffusion. As a matter of fact, how- 

 ever, it is absolutely impossible to lay down any law that appears 

 to regulate the diffusion of the insect. There are instances where it 

 would seem almost impossible to prevent the distribution of the pest, 

 and yet most careful examination has failed to reveal anything of 

 this sort. For a considerable time after the alfalfa weevil became 

 abundant about Salt Lake and Murray hay was shipped from these 

 points to Ely, Nev. This, too, in the midst of the season, when it 

 would seem impossible to transport hay from these points to its 

 destination without carrying greater or less numbers of the weevil. 

 Notwithstanding this, years have gone by, and during the summer 

 of 1911 two assistants examined the country about Ely most care- 

 fully without finding a single alfalfa weevil or any indications that 

 it had ever existed there. While it is possible to account for the 

 spread of the insect theoretically, we can not as yet account for its 

 diffusion to the northeast into adjacent sections of Wyoming and 

 Idaho. It does not appear to have entered Idaho by way of the 

 Cache Valley, although Mr. Titus found beetles on a coal car at 



