INFLUENCE OF TEMPERATURE ON INSECTS. 19 
stumps, but iu hard wood, as oak, etc., associates with Colydium lineola 
and Sosylus costatus, living in their mines. Professor Kiley has dis- 
covered that the larva of Hemirhipus fa scicularis is parasitic on Cyllene 
picta, living in its mines. Strongylium tenuicolle is not a true borer, but 
Mr. Schwarz has found it in the mines of longicoru borers, wherein it 
perhaps lays its eggs. 
Influence of temperature on insect life. — The following statements are 
taken from Judeich and Mtsche's Lehrbuch.and will apply to insects 
in this country: 
"The influence of temperature may either work injuriously on insect 
life from extremes of heat or cold, or from sudden and, at given times 
of the year, abnormal changes. High temperature does not directly in 
our climate, in the natural course of nature, affect insects. On the other 
hand, it is not unfrequently the case that insects, suddenly overcome 
by the frost, freeze to death in great numbers, since with the lowering 
of the temperature, benumbed by the cold, they can not reach crevices 
or holes out of the reach of the frost. As an example, we may refer to 
the winter of 1864-'65, in which, in the district of Mark and the prov- 
ince of Saxony, the caterpillars of pine silk worms and measuring worms 
lemained unusually long on the trees, and the former froze in the mid- 
dle of December,— 12.5° C, and the latter during the considerably 
greater cold in January. Hence the influence of even very great cold 
on the normal hybernating stages of our insects is not very great. In 
the summer of 1854 the 'nun' moth had very generally laid its eggs in 
eastern Prussia uncovered on the bark, and these did not freeze in the 
hard winter of 1854-'55, notwithstanding the expectation that they 
would, based on a temperature of 30 to 35° G. 
"According to the observations of Eegener, openly exposed caterpil- 
lars of the pine silk worm endured —12.5° G. The other stages froze 
earlier, the pupa at —6° 0., the moth at —7.5° G., the eggs at —10° G. 
According to Duclaux (Comptes Eendus, 83, p. 1079) the eggs of the silk 
worm endure well remaining two months in a temperature of —8° C. 
"Great fluctuations of temperature during the winter produce an 
abnormal interruption of the winter's rest or hibernation, and thus cause 
the death of many insects." 
Generations or broods. — The length of time which any insect needs in 
order to complete a single developmental cycle from the time the egg 
is laid until the insect is mature and fit for reproduction is a genera- 
tion ; a generation then is the time from an egg to an egg. The length 
of time of a generation varies, of course, in different insects. Gener- 
ally an insect requires twelve months for its development. In such a 
case we speak of an annual generation. On the other hand an insect 
which requires for its developmental cycle twenty-four, thirty six, or 
forty-eight months has a biennial, triennial, or quadrennial generation. 
The European May beetle has, in northern Germany, a quadrennial -gen- 
eration ; the seventeen -year locust has a generation of seventeen years. 
On the other hand, there are insects which repeat their developmental 
