4S DISTRIBUTION AND DISPERSION OF LEPTINOTARSA. 



Although more or less worn specimens showing the effects of long flight are 

 found year after year in the same localities, it does not breed in these places, 

 and hence this dissemination is futile, as there can be by this means no 

 extension of its bounds. These isolated and sporadic cases of transportation, 

 always accompanying the development of the tropical cyclones, which in 

 the latter part of the summer sweep up through Central America, Mexico, 

 and the United States, have only a remote bearing upon the true dissemina- 

 tion of animals. In the dissemination of L. decemlineata we find a true 

 example of the aid afforded by winds in the dispersion of animals, and not 

 one of the sporadic cases usually mentioned as such, nor one in which the 

 conditions for starting a new colony are too difficult to be realized, excepting 

 in rare instances. 



Other factors also have aided in the dissemination of this beetle temper- 

 ature, moisture, sunshine, food, and soil but of these none have played any- 

 conspicuous part in directing its movements. On the north low temperature 

 and in the south high temperature and high humidity have established 

 seemingly effectual barriers to prevent the beetle from extending beyond its 

 present limits. Between these bounds, however, temperature and moisture 

 are too nearly uniform to be of any moment in the control of dissemination. 

 Food has had a greater influence than the preceding, especially in the south, 

 where the cultivation of the potato is by no means general, and, consequently, 

 the distribution of the beetle has been somewhat retarded and irregular. 



To sum up, in the distribution of L. multiiceniata, intermedia, and decem- 

 lineata over North America the chief directive factors have been: first, 

 habits i, e. , easy flight at the period of its life cycle best adapted for the 

 extension of its bounds ; second, direct response in flight to the direction 

 of winds ; third, climatic barriers to the north and south due to temper- 

 ature and moisture ; and fourth, the amount of its food available. Of these 

 the first is of the greatest importance. If, as has already been pointed out, 

 a period of easy flight had not previously been developed, probably no dissem- 

 ination could have taken place. The development of this habit dates far 

 back in the history of the species, certainly to the time when midtitccniata 

 began to spread out over northern Mexico, if not earlier. Previous to the 

 beginning of this dissemination it was of no very general importance in the 

 economy of the species, but changes in the environment resulted in the 

 raising of this habit into one of prime importance as far as ability to undergo 

 rapid dispersal was concerned. Now that the dissemination is over for the 

 present, this habit again sinks into a position of relatively small importance 

 in the economy of the species. While emphasizing the importance of this 

 habit, I do not mean to underestimate the influence of environment upon 

 the spread of this beetle, but I do believe that we must understand better 

 the habits and constitution of an organism before we decide concerning the 

 relative potency of the various factors in its distribution and evolution. 



