29 



spot appeared 2 to 3 days later. This shorter averaoe ma}' he 

 accounted for by the fact that these egj^'s were kept at a higher tem- 

 perature than normal. 



METHODS OF OBTAINING EGGS. 



There are two wa3's of obtaining- eggs for .stud^^ The first i.s to 

 collect them in the field and place them under observation in cages. 

 There is a .serious ol)jection to this method, as there is no way of 

 knowing the age of the eggs. The second method, that of confining 

 larva? and pupw and allowing the moth.s to emerge, is far more satis- 

 factory. If these moths are plac-ed in a cage over a limb of a tree, 

 one wall find eggs in abimdance in a dav or two. One is sometimes 

 fortunate enough to find moths in co})ula, and in that event they 

 should be placed in a separate cage. By determination of sex of the 

 various moths much more valuable data can ])e secured. Care must 

 be taken that too many eggs are not laid in one cage, as in that event 

 it is difficult to keep accurate notes. 



These limb cages are bags made of mosquito netting of finer mesh 

 than the ordinary netting. By this method the leaves and- fruit are 

 always fresh and the conditions are exactlv the same as in the orchard. 



INFLUENCE OF TEMPERATURE UPON THE LENGTH OF THE EGG STAGE. 



It has often been stated that a higher temperature caused the eggs 

 to hatch in a shorter time, but onl}' a few definite observations have 

 been recorded. The temperature used in these calculations is the 

 effective temperature, which is ol)tained b}' subtracting •13-' from the 

 mean daily temperature as recorded by the United States Weather 

 Bureau station at Boise, Idaho. 



Professor Gillette gives 6i days as the length of this stage at a tem- 

 perature of from 68^ to 70"^ F. and 6 days as the time in a greenhouse 

 where the temperature was 110'-' F. at midday. In Table I the total 

 and average effective temperature is given from the time the eggs 

 were laid until they were hatched. These data are arranged accord- 

 ing to the temperature in Table II. 



Table II. — Effective temperature, and jieriad of Ineuhatioii. 



Average total effective temperature, 302° i^. 



