Studies on Eggs op Apple Plant Lice 59 



there was little or no reduction in the percentage of hatch. This 

 solution was also mixed with lime-sulfur (G-16, table 4) with no 

 apparent change in the results. It was also combined with crude 

 carbolic acid (exp. 0-79, table 4) at the rate of 1 part of each to 

 100 cc. of soapy water, and the percentage of hatch was reduced to 

 13.3 per cent. This decided decrease was unquestionably due to the 

 crude carbolic acid. The pyridine mixture is highly volatile and 

 this may account for its ineffectiveness. 



Summary 



In the summary onl}^ the new and important features of this 

 investigation will be considered. 



A morphological study of the eggs of three apple plant lice 

 A. avence, A. pomi and A. sorbi shows two distinct layers in the egg 

 shell, an outer semi-transparent layer which is soft and glutinous 

 when the egg is deposited, but hardens and becomes somewhat tough 

 (may be brittle) and impervious upon long exposure to weather, 

 and an inner soft, elastic, membraneous, black layer. A third layer 

 thin and membraneous, may be seen about the nymph when it starts 

 to emerge. This skin is probably the first exuvium, since it is shed 

 by the nymph as it emerges. 



Under out-of-door conditions the outer layer of the egg usually 

 splits along the dorso-mesal line a number of days (2 to 30 or more 

 for A. avence) before the nymph emerges. So far as observed under 

 greenhouse conditions the eggs of all three species split their outer 

 covering at least a few liours before the pigmented layer is severed. 

 In 1918 the first eggs of .4. avenoi with split outer coverings were 

 seen on February 15, and when the first nymphs emerged, on March 

 21, approximately 95 per cent of the normal live eggs (45-50 per 

 cent of the eggs were dead) had split their outer semi- transparent 

 covering. 



These observations on the morphology and behavior of the egg 

 coverings show conclusively that the egg is not a hard resistant 

 body, and that it goes through a critical change previous to the 

 emergence of the nymph. It is in the midst of this critical period 

 that the egg is most susceptible to evaporating factors and certain 

 contact insecticides. 



The outer semi-transparent layer of the egg is somewhat im- 

 pervious to water; consequently, the water content of the embryo 

 does not undergo very much evaporation in moist weather, or in 

 other words, when low evaporating factors exist, such as high 

 humidity, low temperature, and probably small wind velicity. The 

 outer layer, however, is not entirely impervious, for extreme drought 



