Studies on Eggs of Apple Plant Lice 7 



as much. In 1918 the eggs of A. avence started to hatch on March 

 21, and completed hatching on April 5. This early hatch was un- 

 doubtedly due to the unusually warm weather during IMarch, 1918. 

 The percentage of eggs which hatch varies among the different 

 species (compare the percentage of hatch in the different checks). 

 Out of 1200 eggs of A. aveme, 50 per cent hatched in 1917, while in 

 19] 8 only 30 per cent hatched out of 1800 eggs. The percentage of 

 hatch in the different checks may vary considerably (25 per cent), 

 when only a few eggs (50 to 100) are observed. The decided dif- 

 ference in the percentage of hatch for 1917 and for 1918 of this 

 species is probably due to climatic conditions. The eggs of A. ponii 

 and A. sorhi during 1916-17 were mixed together on the twigs 

 used in the experiments (approximately 70 and 30 per cent, 

 respectively), and this makes it impossible to determine the 

 percentage of hatch for each, but out of 800 eggs in this mixture, 

 the hatch was close to 25 per cent. The percentage of hatch for A. 

 pomi is probably somewhat lower than that of A. sorhi, for the eg'gs 

 of A. pomi are scattered promiscuously over the surface of the twigs 

 and thus exposed to accident and to unfavorable weather conditions. 

 The above percentages of hatch are considerably higher than those 

 recorded by other investigators. Gillette, in Colorado, observed 

 that only 1 per cent of the eggs of A. pomi hatched. This seems ex- 

 ceptionally low ; however, environmental factors, such as a low per- 

 centage of humidity, may bring about this decided reeduction. 



Methods 



All records in the table which pertain to the condition of the 

 eggs, were made by carefully observing each e^^ under a binocular 

 microscope and then noting whether it was normal, split, hatched 

 or shriveled. In this way one can readily distinguish a normal egg 

 by its plump and well rounded appearance an(J homogenous surface 

 (plate 1, fig. 1), an e^g with its outer semi-transparent covering 

 split shows a distinct glossy black streak p usually along the meso- 

 dorsal line (plate 1, fig. 2 to 5), a hatched egg possesses a distinct 

 opening in its surface (fig. 8 and 9), and a shriveled egg is dry 

 and collapsed (plate 1, tig. 11 and 12). 



During 1916-17 approximately 10,000 eggs were carefully ob- 

 served, while in 1917-18 over 40,000 eggs were used in the various 

 experiments, and a careful record was made for each egg. AVhen- 

 ever material was needed for experimental purposes, collections 

 were made from the above-mentioned orchards and in all 

 cases this material, when used for out-of-door experiments, was 

 kept out-of-doors and-exposcd to all conditions of the weather, ex- 

 cept for the few minutes required to examine the eggs under a 



