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possible for breeding to be more nearly continuous. The instinct of 

 this and other insects of recent southern origin is still to remain late 

 feeding in the open, provided appropriate plants are available for their 

 subsistence, or, to put it otherwise, they have not learned to seek 

 shelter at the same time as native or acclimated forms do. 



Recent observations on this and other species of similar habits and 

 origin suggest that the ancestors of those individuals which produce 

 onty a single generation were introduced in early times and are thor- 

 oughly established and acclimated, while those which produce a second 

 generation are the offspring of ancestors which have spread from the 

 south more recently and have not yet become accustomed to the differ- 

 ences in the weather in the North and in the South. 



The development of two generations by Melittia and other southern 

 introductions in the District of Columbia and places having a similar 

 climate is a matter apparently not so much dependent on the weather 

 as upon the inability of the insects to find the appropriate food for 

 their larvse; for example, were cucurbits to be planted earlier and 

 later, there would be no trouble in the vine borer producing two well- 

 marked generations in spite of the fact that the vines of cucurbits are 

 readily killed by frosts, the insect being able to survive upon stems 

 which are not of the freshest. 



Certain species recently observed, e. g. , PluteUa cruciferarum, the 

 diamond-back cabbage moth, there are the best of reasons for believing 

 are able to produce an additional generation during the latter days of 

 November and the first week of December, as many larvse captured at 

 this time were full grown and accompanied by numerous pupas, most 

 of the individuals captured changing to pupse before the end of the 

 first week of December, in which condition they would naturally be 

 less exposed to frost and better able to survive the rigors of winter. 

 Still another generation, however, was attempted, as one moth cap- 

 tured deposited its eggs at this time. This generation was, of course, 

 doomed to failure. 



The effort on the part of so many introduced Old World species of 

 producing extra generations would naturally lead to the belief that 

 these insects came originally and in comparatively recent times from 

 southern Europe or southern Asia, became acclimated farther north in 

 Europe in the same manner that native Southern forms become estab- 

 lished by migration to our Northern States, whence they were intro- 

 duced in the Upper Austral portions of the United States, for the most 

 part about oar principal seaports, Boston, New York, and in some cases 

 Baltimore, and in other large cities, such as Philadelphia and perhaps 

 Washington, and after becoming adapted, more or less imperfectly 

 perhaps, to the environment of those cities, have made their way still 

 farther south, where they have again resumed what was probably their 

 original habit of producing two, three, or more annual generations. 



