Studies on Eggs of Apple Plant Lice 29 



time when the nymphs emerge. In all the experiments, no matter 

 what substance was used, the percentage of hatched eggs was less 

 when the substance was applied on March 23 than when applied 

 in December, January, Februar}^ or March 4. 



Briefly stated, the greatest number of eggs are killed in all 

 the experiments when the spray is applied just prior to the 

 emergence of the nymph. This gradual increase in susceptibility 

 is dependent upon the increase in the percentage of eggs showing 

 split outer shells. On the basis of the facts shown in the chart and 

 from foregoing observations on the morphology and behavior of 

 the egg previous to the emergence of the nymph, we may conclude 

 that the greater the percentage of eggs possessing split outer shells 

 the greater will be the percentage of dead eggs when contact in- 

 secticides are used. 



Lime-Sulfur 



A large number of experiments were conducted on the eggs 

 of all the species in the greenhouse, out-of-doors at the laboratory, 

 and in various orchards during the past two seasons, using different 

 strengths of lime-sulfur and lime-sulfur combined with nicotine. 

 During February, March and April, 1917, experiments G-12 to G-17 

 and 0-18 to 0-25 (table 4), were performed in the greenhouse (G) 

 and out-of-doors (0) with the eggs of all three species, and the 

 results show a very decided reduction in the percentage of hatched 

 eggs and in some instances a complete kill. Eggs of A. avence 

 sprayed with lime-sulfur 1-8 and kept under greenhouse conditions 

 or out-of-doors at the laboratory showed a very small percentage 

 of hatch or a complete kill (3.9 to 0.0. per cent hatch). Eggs of 

 A. pomi receiving similar treatment showed a 2.0 to 7.3 per cent 

 hatch. A comparison of these percentages among the two pre- 

 dominant species in the respective experiments shows that the eggs 

 of A. avenm are more susceptible to lime-sulfur than A. pomi. 

 Lime-sulfur 1-6 and greater strengths gave better control than 1-8 

 or 1-9. 



In a few experiments lime-sulfur w^as combined with sodium 

 chloride, a pyridine solution and nicotine sulfate. The results of 

 the experiments with the first two chemicals mentioned are dis- 

 cussed under other chemicals. During 1917 one experiment (exp. 

 0-25, table 4) was conducted out-of-doors at the laboratory with 

 the eggs of A. pomi where nicotine, ''Black-leaf -40", was used at 

 the rate of 1-500 and the percentage of hatch was 0.9 per cent, 

 while another experiiiient with lime-sulfur, 1-8 (exp. 0.24, table 4) 

 gave a 4.6 per cent hatch. These results indicated the possibility 

 of obtaining a more perfect control when a combination spray was 

 used, consequently a large number of experiments were conducted 



