INFLUENCE OF TEMPERATURE ON INSECTS. 19 



stumps, but in hard wood, as oak, etc., associates with Colydium lineola 

 and Sosylus costatus, liviug: iu tlieir mines. Professor Riley has dis- 

 covered th at the larva of Hemirhipus fascicularis is parasitic on Cyllene 

 picta, living in its mines. Strongylium tenuicolleis not a true borer, but 

 Mr. Schwarz has found it in the mines of longicorn borers, wherein it 

 perhaps lays its eggs. 



Influence of temperature on insect life. — The following statements are 

 taken from Judeich and Nitsche'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 

 oar 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,— 12.50 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 Regener, openly exposed caterpil- 

 lars of the pine silk worm endured —12.5° C. The other stages froze 

 earlier, the pupa at —6° C, the moth at —7.5° C, the eggs at —10° 0. 

 According to Duclaux (Comptes Rendus, 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 



