EFFECTS OF HABITS IN DISPERSAL. 45 



they remain active for about three weeks, or even longer, in the autumn, 

 before seeking a place in which to hibernate. It was in this interval 

 between the emergence of the second brood and the beginning of its hiberna- 

 tion that most of the area of advance was covered. During this time both 

 sexes are active ; the females are not laden with ripe ova, and are therefore 

 able to fly with greater ease than in the following spring, or than are the 

 females of the first summer brood. Riley notes that the fall brood has a 

 tendency to migrate. He records seeing them ' ' swarming in the air or 

 traveling on foot," and he believes that " most of the advance ground was 

 covered in the latter part of the growing season." Under the best of condi- 

 tions this insect is a poor flyer without outside aid ; it can be driven some 

 distance, but when undisturbed it never flies far without settling down to rest. 



The existence of this active period was of great importance in the advance 

 eastward. The females, when laden with ripe ova, fly with difficulty, and 

 only small distances are covered before the eggs are deposited. Hence, if 

 the second brood had paired and deposited its eggs within a few days after 

 emergence, as did the first, it is evident that there would have been but little 

 flying about, and as a result its advance would have been far less rapid and 

 the history of its dissemination quite different. If we compare L. decem- 

 lineata with Ocneria dispar in its spread over Massachusetts, the importance 

 of a period of free and easy movement in the life cycle as an aid in rapid 

 dissemination is at once apparent. In O. dispar the spread has been exceed- 

 ingly slow, owing in part to the inability of the females to fly, but as much 

 or more to the short time the female imago lives. The female is fertilized 

 almost immediately upon hatching from the pupa, deposits her eggs within 

 a few feet of the spot where the larval and pupal stages have been passed, 

 and then dies. If the female moved about for three or four weeks and 

 then hibernated, and did not deposit her eggs until the next spring, all 

 other conditions remaining the same as at present, the spread of this insect 

 would have been much more rapid and its partial subjection a much greater 

 task than the State has found it. The existence and duration of this period 

 of free and active movement is a factor of prime importance in determining 

 the rate of dissemination of any insect, and must, I think, in the case of 

 introduced insect pests, receive due consideration in the discussion of the 

 probability of suppression or the possibility of extermination. 



In the eastward spread of the beetle it early became evident that the 

 advance was more rapid in some directions than in others, and this accelera- 

 tion and retardation have been found throughout its whole history. I have 

 shown that there was little transportation by human agencies, and further 

 that the insect is a poor flyer ; hence the covering of the wide stretches of 

 country that were overrun year by year required some outside aid. This 

 aid I have found to come largely from winds, as is demonstrated by the 

 following experiments : On a clear, calm day in August or early September 



