Studies on Eggs op Apple Plant Lice 21 



extent by weather conditions, especially during the few weeks 

 previous to the emergence of the nymph. In brief, the existence 

 of high evaporating factors during the dormant season, especially 

 after the outer egg shell has split, kills a large number of eggs 

 which would normally complete the process of hatching in weather 

 with low evaporating factors. In order that the above relationship 

 between the percentage of hatch and the condition of the weather 

 may be proved and its significance ascertained, especially in regions 

 where the average humidity is low, it is suggested that observations 

 be made in various states, on the percentage of hatch for the various 

 species concerned. 



Temperature 



Temperature has a marked and peculiar influence upon the 

 hatching of the eggs of all three species. Some of these influences 

 have been mentioned. In 1917 eggs of A. pomi and A. sorhi were 

 brought into the greenhouse during February and the early part of 

 March (up to March 14) and these failed to hatch, while eggs of 

 .4. aveme brought into the greenhouse at the same time showed a 

 normal percentage of hatch. During 1917-18 eggs of A. aveme 

 collected in November and placed in the greenhouse showed a 

 10 per cent hatch during the first week in Febniary, while eggs 

 collected on February 26, and put in a moist chamber in the labora- 

 tory showed a 43.5 per cent hatch. This difference in the per- 

 centage of hatch (also true for other experiments during December 

 and JanuarjO may be due to the fact that an exposure to low 

 temperatures is beneficial for the majority of the eggs of A. avencv. 

 As noted before, the greenhouse was closed early in February 

 during 1918 and the transfer of the eggs to a moist tin compart- 

 ment in the laboratory may have had some influence on the per- 

 centage of hatch. In order to be sure of the above statement con- 

 cerning the eggs of A. avence it will be necessary to repeat these 

 experiments. Egg's of A. pomi and A. sorbi will hatch under 

 laboratory or greenhouse conditions provided they are not brought 

 into the laboratory or greenhouse over 20 to 30 days before they 

 normally hatch out-of-doors. The above peculiarity in the hatching 

 of the eggs has also been noted by Baker and Turner (2) and other 

 investigators. For some unknown reason, long exposure to low tem- 

 peratures is essential for the normal development of the embryo of 

 A. pomi and A. sorbi, and it may be beneficial for the majority 

 of the eggs of A. avence. 



Temperature also influences the egg when it is preparing to 

 hatch. It was repeatedly noted that the percentage of eggs with 

 a split outer covering would always show a decided increase during 

 or following a day or two of exceptionally warm weather. This 

 was particularly true during the latter part of February and the 



