46 
DR ALFRED E. CAMERON. 
the surface, January 1913, 38° F., January 1914, 44° F., an increase of 6° F. Ana- 
logous variations were recorded for February and March, with an increase of tem- 
perature in 1914 favourable to the earlier emergence of insect species from their 
hibernating quarters, a fact which was actually observed during the latter year. 
The facts regarding the relationship of temperature to the hibernation, sestivation, 
and growth of insects are but inadequately known. Several workers have recently 
made notable contributions to the subject, of which those of Tower, Sanderson, 
Headlee, and Dean in America, and Bachmetjew in Europe are important. 
Sanderson # has endeavoured to determine the existence of physical laws upon 
which the time of emergence of insects from hibernation and the date upon which 
they begin oviposition, depends. In experiments with the brown-tail moth ( Euproctis 
chrysorrhoea) , the tent caterpillar ( Malacosoma americana), and the codling moth 
( Carpocapsa pomonella), he has also endeavoured to establish a “ thermal constant” 
governing the emergence of insects from hibernation. “ Thermal constant” is defined 
as that accumulation of mean daily temperature above the “ critical point ” of the 
species which will cause it to emerge from hibernation or to transform from any 
given stage. Active metabolism in insect species as well as in plants only occurs at 
or above a certain temperature, probably specific for each kind or group, and this 
temperature has been designated the “critical point” for the species concerned. 
Heretofore 43° F. was generally accepted as being the universal temperature at or 
above which all temperatures were effective, but recent work has proved that it 
varies for different species. 
It has generally been accepted that a lowering of temperature causes or is at 
least associated with the phenomena of hibernation, but Sanderson ( loc . cit. p. 58) 
and Tower f have shown that insects have persisted in hibernating, or at least have 
their activities curtailed, in spite of being subjected to high temperature just pre- 
vious to the normal time for hibernating. The latter author asserts that all the 
species of the genus Leptinotarsa, which includes the notorious Colorado potato 
beetle, have but two generations, when a period of rest, hibernation, or aestivation 
ensues, either of which exert the same effect on the life-history phenomena of the 
insect. During the period of rest the insect loses about 30 per cent, water, causing 
a concentration of its protoplasm and body fluids, by virtue of which it can the more 
readily resist the injurious effects of lower and higher temperatures. 
Sanderson } in a later paper also draws attention to the fact that for some species 
moisture content is very important, and often more so than temperature, in deter- 
mining the optimum for development ; and therefore it is necessary for accurate 
work on the effect of temperature that moisture conditions should be kept constant. 
* Sanderson, E. D., “The Relation of Temperature to the Hibernation of Insects,” Jour. Econ. Ent., vol. i, 
No. 1, pp. 56-65, 2 figs. 
t Tower, D. L., Evolution in Chrysomelid Beetles of the Genus Leptinotarsa, Carnegie Institution, No. 48, 1906. 
f Sanderson, E. D., “The Relation of the Temperature to the Growth of Insects,” Jour. Econ. Ent., 1910, 
vol. iii, No. 2, p. 121. 
