Studies on Eggs of Apple Plant Lice 17 



registered 80° F., and each was fitted with one moisture-control 

 apparatus; one contained dry air which always registered less than 

 0.5 per cent moisture, another air of 22 per cent moisture, the third 

 about 63 per cent moisture, and the fourth air completely saturated. 

 Practicalh' no variation occurred in the dry air and in the satura- 

 ted, while in the case of 22 and 63 per cent moistures the amount 

 occasionally fluctuated 1 to 5 per cent. The eggs were carefully 

 selected and removed from the twigs by cutting the bark adjacent 

 to them, or very small twigs bearing numerous eggs were chosen, and 

 these placed in 80cc. glass bottles fitted with rul)ber stoppers having 

 two short glass tubes which connected the bottle with the moisture- 

 control equipment. 



Table 1 shows tlu^ results of a few incubator experiments con- 

 ducted with A. ovciia- -and A. pomi. The various columns are self 

 explanatory ; the second from the right gives the total percentage of 

 hatch of all the eggs after all hatched or shriveled, and the column 

 to the extreme right gives the number of days required to shrivel 

 and kill all the eggs. The percentage of hatch might have varied 

 a little in the difi'erent experiments if a larger number of eggs had 

 been used; however, the results unquestionabl}' show that different 

 percentages of moisture have a decided influence on the emergence 

 of the nymph. The largest percentage of hatch occurred in satura- 

 ted air, and practically no hatch in dry air. This decided influence 

 of moisture probably accounts for the low percentage of hatch 

 recorded for A. j)omi by Gillette (6), in Colorado, where the rela- 

 tive humidity of the climate is much less than at New Brunswick, 

 N.J. 



The rate of shrivel of the eggs in the different percentages of 

 moisture in all the experiments is also significant. This is par- 

 ticularly true in the experiments with the eggs of A. pomi (exp. 

 109-112) which never hatched. Eggs of A. pomi will not hatch 

 when brought into greenhouse or laboratory temperatures unless 

 it is near the normal out-of-door hatching period, not over 20 to 30 

 days before hatching. 



In experiments 109-112 dry air completely shriveled the eggs 

 in 7 days while saturated air required 24 days. In other words, in 

 these experiments and also in all others pertaining to moisture, the 

 rate of shrivel shows that the water evaporated from eggs in dry 

 air, or 22 per cent humidity, in one-half to one-third the time re- 

 quired for eggs under 63 per cent moisture, or complete saturation. 

 Comparing the rate of shrivel of the eggs in experiments 109-112 

 started on :March 14 wdth those of the same species (exp. 105-108) 

 started on April 6, the eggs of the latter shriveled more rapidly. 

 This increase in the rate of shrivel is closely correlated with the 

 greater percentage of eggs shoAving split outer coverings near the 

 hatching period. 



