425 



Florence (L.). The Pacific Coast Species of Xylococcus (Scale-Insects). 

 — Ann. Entom. Soc. America, Columbus, Ohio, x, no. 2, June 

 1917, pp. 147-166, 4 plates. 



The follo'unng species are described, with notes on their Kfe-histories : 

 Xylococcus macrocarpae, Cole, found on Monterey cypress {Cupressus 

 macrocarpa) ; X. quercus, Ehrh., on Quercus chrysolepis ; X. alni, sp. n., 

 on alder. A table is given of the North American species of Xylococcus. 



Baumberger (J. p.). Hibernation: A Periodical Phenomenon. — Ann. 

 Entom. Soc. America, Columbus, Ohio, x, no. 2, June 1917, 

 pp. 179-186. 



Various hypotheses have been proposed regarding the causes of the 

 quiescent condition of many insects during winter which is known as 

 hibernation. The most common explanation offered is that low 

 temperature or low mean temperature is conducive to hibernation. 

 Experiments carried on during the past two years with the banana 

 fly, Drosophila melanogaster , Mg., have show^l, however, that a 

 persistent quiescent condition was in no case brought about by the 

 stimulus of low temperatures, larvae and adults after 20 days in an 

 ice box being immediately activated by restoration to high tempera- 

 ture. The stimulus of relative humidity was determined by 

 experiments on the caterpillars of Isia Isabella and Apantesis nais, 

 which hibernate as larvae at a definite date, irrespective of low 

 temperatures. In these cases, high temperature, abundant fresh food 

 and any relative humidity was found an insufficient stimulus to 

 overcome the tendency of the insects to hibernate. Consequently, it 

 is evident that the state of quiescence is predetermined. 



In previous experiments with Lasiocampa quercus, which hibernates 

 before the temperature has lowered, by keeping larvae on ice it was 

 possible to cause them to pupate in May, and continued selection of 

 precocious larvae for six generations decreased the length of the larval 

 stage from 245 to 112 days. The pupa! period was lengthened 

 sufficiently to make up the difference. Similar experiments with 

 Dendrolimus pini gave a second generation and no persistence of the 

 normal cycle. This may be due to the fact that L. quercus feeds on 

 the leaves of deciduous trees, while the food of D. pini is evergreen. 

 There is thus a variability in the characteristic feature of 

 hibernation; certain insects have a definite periodical hibernation 

 which is hereditary, and if this quiescence be overcome by artificial 

 means, the insects, by a compensatory lengthening of the next stage, 

 regain the normal rhythm of existence. Other insects are more plastic, 

 merely remaining quiescent during periods of low temperature and 

 regaining activity immediately after the temperature is raised ; such are 

 Drosophila, Cirphis (Noctua) unipuncla, cockroaches, Musca domestica 

 and others. The factors determining this variability are : (1) Climate, 

 Insects do not hibernate in the tropics, w^here there is no cold period, 

 and if introduced into temperate regions cannot be induced to hiber- 

 nate. (2) Food. Insects which feed on materials constantly available 

 do not show a definite periodicity. Thus the house-fly will oviposit 

 at any time of year in appropriate temperature, and insects which feed 



