20 
FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 
cycle two, three, or more times in a year; such insects are said to be 
doable or treble-brooded. Lopkyrui abietti and other species are double- 
brooded, while many butterflies are doable or treble brooded, and the 
Aphides have from nine to fourteen generations in a season, i. e., from 
Spring to autumn. In all cases of seasonal dimorphism or of partheno- 
genesis there are several generations. 
Jadeich and Nitsche graphically represent as follows the generations 
of the European Lopkyrty pint, with its double generations, which will 
also apply to our L. (thirds: The egg is denoted by a point ( • ), the 
larva by a dash ( — ), the larva lying in a semi-papa condition in the 
cocoon, thus ( O ) ; the papa by the following mark ( m ), and the imago 
by a cross ( -\- ) ; the time during which the larva is eating, by a heavy 
dash HI i; lastly, the period of injury by the larva is placed under, 
the time of imaginal injury above, the mark for the stage under consid- 
eration. 
Jan. Feb. 
Mar. 
Apr. May. Jane. 
July. 
Aug. 
Sept. 
Oct. 
Nov. 
Dec. 
+ + 
• • 
••+ 
+ 
1860. 
-6esosea3 
BflHBHBH 
■OTMH 
• t- + 
• • 
1881. 
In the United States a butterfly or moth which is siugle-btooded in the 
New England or northern Central States may be three-brooded in the 
Southern or Gulf States. A generation or brood which appears and 
ends in the summer is shorter than that which hibernates. 
Thus the summer generation of the species of pine saw-flies (Lophyrus) 
is about four mouths, the winter generation about eight months. 
Hence the leugth of the generation depends on the temperature and 
climate, as does also the number of broods or generatious. "This influ- 
ence of climate is, as is well known, so considerable that a species of 
insect which has a double generation in a certain locality, in another 
place with a colder climate is only single-brooded, while in a warmer 
climate it is three-brooded. An example is Rylesinus piniperda. Thus 
also a species of insect whose generations in a certain middle location 
is, for example, four-yearly, in a more southern situation is three-yearly. 
A proof of this is afforded by the May beetle, which north of the ' main 
line' is four, but south of it needs only three years to complete its 
development. A certain species of insect may moreover in the same 
locality in a warmer and more favorable year be double-brooded, while 
in the next harsher unfavorable year it is single-brooded. But if the 
checking influence of the harsh weather is less, then even in an un- 
favorable year a second generation may begin to develop, but does not 
complete its cycle by the end of twelve months. Hence there are in 
twenty-four months three generations, and then arises what Ratzeburg 
calls a 'one-and-a-half generation.' Of this Tomicus bidentatus not rarely 
affords an example. 
