46 DISTRIBUTION AND DISPE^RSION O^ LEPTINOTARSA. 



put mature, active beetles in a shallow tray mounted on a tripod or other 

 support. In an hour or so all of the beetles will have crawled out and the 

 larger part will have taken flight from the edges of the tray ; but the 

 directions of these flights will be as many as there are beetles. Under such 

 conditions there is no one direction in which they show a tendency to travel. 

 In fact there is not, as has been stated by Riley, Walsh, and others, any 

 instinct or tendency that causes them to migrate in a certain direction. 

 This experiment has been tried many times in Massachusetts, on Long 

 Island, New York, in the Ohio River Valley, and on the shores of Lake 

 Michigan, and always with the same result as that given above. But let 

 the same experiment be tried on a day when a steady breeze is blowing 6 to 

 8 miles an hour, but with other conditions similar, and a strikingly different 

 result is obtained. The beetles all start out from the tray as before in as 

 many different directions as there are beetles, but when the direction is 

 against or even across the wind they soon become tired with their exertions 

 and drift with the wind, often for a considerable distance. These experi- 

 ments and close observation of the beetles as they start of their own accord 

 from their food plant have uniformly given the same result — that while the 

 beetle is able to fly some distance against a strong wind, it almost invariably 

 turns and drifts back with the wind for a much greater distance than it has 

 flown against it, the actual or net movement or migration being in the 

 direction of the wind, i. e., with the wind. 



The influence of the wind is well shown along the Atlantic coast or the 

 shores of Lake Michigan when there is an ' ' offshore ' ' breeze. The beetles 

 are then carried out over the water and, becoming exhausted, fall to the 

 surface, where they float, and not infrequently are washed ashore in such 

 numbers that they form a small windrow along the beach. In 1876, when 

 they were abundant along the Atlantic coast, they were blown out to sea in 

 large numbers, and, being washed back upon the beaches, were so numerous 

 that they were obnoxious to the pleasure seekers there. 



The ease with which the wind determines the direction of flight of this 

 beetle is well known on the shores of Massachusetts, where an on-shore 

 breeze is often well developed for days at a time. Then the beetles are 

 found flying awa}^ from the shore or crawling about on objects to the leeward 

 of the potato patches from which they started, and if a nearby beach be 

 searched very few living or freshly killed beetles will be found. But let 

 this sea breeze be overpowered by the prevailing westerlies, as it often is, 

 and the beetles are all found to be flying wdth the wind or driven by it 

 toward the sea, and if the beach be searched a day or two later there will 

 be found numbers of freshly killed or living beetles. 



On plate 8 is plotted by means of arrows the prevailing wind direction 

 for the months from May to September, inclusive. It is evident that the 

 lines of most rapid advance are correlated with the prevailing wind direction 



