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SOME OBSERVATIONS ON THE EGG OF 

 PSYLLA MALL 



By A. H. LEES, M.A., 



Plant Pathologist, University of Bristol, Agricultural and 

 Horticultural Research Station. 



For some years it has been known that the egg of the Apple Sucker, 

 Psylla mali, hatches at slightly different times on different varieties 

 of apple trees. Theobald in his Insect Pests of Fruit makes the following 

 remarks : 



" Another point of great interest concerning the eggs is the irregularity 

 with which they hatch out. The date not only varies in different 

 localities and in different years but during the same season in the 

 same plantation. They incubate at different periods according to 

 the variety of apple upon which they are situated. This may be due 

 to the heat generated by the flow of sap regulating their hatching 

 to the time of the bursting of the buds." 



So close was the correspondence between the date of bud bursting 

 and egg hatching that it appeared as if there might be some intimate 

 relation between the egg and the host plant. Investigations were 

 therefore begun by the author in 1911 but owing to lack of opportunity 

 could not be continued till 1915. A description of the egg may be found 

 in Theobald's Insect Pests of Fruit where a certain process of the egg is 

 mentioned and figured. He describes the egg thus: 



"The ova when first laid are almost white, then they become creamy 

 yellow and later assume a faintly rusty-red hue before hatching. 

 Furley describes them as becoming a pale yellow-red also. They are 

 elongated oval in form, somewhat pointed at the ends, one of which 

 is produced into a thin process which is apparently curled under the 

 egg and cannot easily be seen unless the ovum is very carefully removed. 

 What this process is for we do not at present know." 



Under ordinary circumstances this is the only process that can 



