79 
TENDENCY OF INTRODUCED FORMS TO PRODUCE EXTRA GENERATIONS 
IN ADOPTED NORTHERN HABITATS. 
European introductions in the United States frequently produce one 
or more generations in excess of the number that has been observed 
and recorded in the northern countries of Kurope where observations 
have been made, and even attempt generations late in the year, which 
are often apt to perish by being overtaken by frosts before trans- 
formation can be accomplished or suitable places sought out for 
hibernation. 
Southern forms that migrate northward in time appear to become 
perfectly at home in northern localities; in fact, thoroughly acclima- 
ted, but this is apparent only, as there is every reason to believe that 
many species attempt the production of one or more generations more 
than similar northern species have; or, in other words, essay the 
normal generations which they had in the south, which are apt to be 
cut short by intervening cold weather before their completion. 
Examples of both forms are apparently more frequent in leaf- 
feeding mandibulates, particularly the larve of Heterocera or moths 
and phytophagous Coleoptera, especially Chrysomelidee or leaf-bettles. 
Several injurious forms of plant-lice are in the same category, although 
these have not been given special study. Many genera are known to 
feed in cold weather long after frosts, and may even be taken on their 
host plants under the snow. 
An excellent illustration of polygneutism, or the production of sey- 
eral generations annually ina species recorded as normally monogneutic 
in its native home, is to be found in the imported elm leaf-beetle, 
Galerucella luteola. There can be little doubt that this species is 
monogneutic in Kurope, but observations conducted at New Bruns- 
wick, N. J., and Connecticut cities in the Upper Austral life area 
have shown that there is an incomplete second generation. In the 
more southern portions of the same life area there are invariably two 
generations annually, and in exceptional seasons a third generation 
is attempted; at Hee beetles of the second generation have been 
observed to lay eggs.’ 
An example of an extra generation being produced by a southern 
species is found in the squash-vine borer, Jelittia satyriniformis, 
which is single-brooded on Long Island and northward, apparently 
single and partially double- brooded i in New Jersey, while in the lati- 
tude of the District of Columbia the species is both single- and double- 
brooded, as shown by the writer in recent years (Bul. No. 19, n. s. Div. 
Ent., p. 39). This peculiarity in reproduction is evidently a survival 
of the time when this species lived in a tropical climate, where it was 
‘Even some of our native species closely allied to the elm leaf-beetle, e. g., Gale- 
rucella americana Fab., have been observed by the writer to lay eggs for a second 
generation late in July (Proc. Ent. Soc. Wash., Vol. III, p. 275), but this is, with 
little doubt, exceptional. 
