42 BULLETIN 173, U. S. DEPARTMENT OF AGRICULTURE. 



Table IX. — Length of egg stage of the pear thrips, San Jose, Cal., 1910 — Continued. 



Cage 



Date de- 



Date 



Number 



of eggs 



hatched. 



Length 

 of egg 

 stage. 



Average 

 mean 



Prevailing 



No- 



posited. 



hatched. 



tempera- 

 ture. 



weather. 











Days. 



"F. 





VII 



Mar. 29 



Apr. 3 









56 



Clear. 







8 





10 



56 



Do. 



VIII 



Mar. 29 



Apr. 7 





9 



56 



Clear. 







8 





10 



56 



Do. 







9 





11 



56 



Do. 







10 





12 



56 



Do. 



IX 



Mar. 29 



Apr. 2 





4 



57 



Clear. 







6 





8 



56 



Do. 







7 





9 



56 



Do. 







8 





10 



56 



Do. 







10 





12 



56 



Do. 







14 





16 



55 



Do. 



X 



Apr. 6 



Apr. 12 





6 



54 



Cloudy. 



XI 



Apr. 6 



Apr. 13 





7 



54 



Cloudy. 



XII 



Apr. 6 



Apr. 13 





7 



54 



Cloudy. 



SUMMARY. 



Number eggs deposited. 



Time 



required for 

 incubation. 



Number eggs deposited. 



Time 

 required for 

 incubation. 



1 



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Days. 



4 

 5 

 6 



7 

 8 

 9 



34 



Days. 

 10 

 11 

 12 

 13 

 14 

 16 



7 .. 



24... 



44... 



4 . 



49 



4 







For the 296 eggs under observation, the maximum length of the 

 egg stage was 16 days, and the minimum 4 days, making 8.3 days 

 the average time required for incubation. 



The eggs of the pear thrips are undoubtedly affected by tempera- 

 ture conditions, but rainy weather as compared with clear weather 

 seems to make no difference when the mean temperature is the same, 

 as all eggs are embedded in the moist plant tissue and do not require 

 additional moisture from the atmosphere. 



It is evident that all of the eggs are not in the same stage of develop- 

 ment at the time they leave the abdomen of the female, since eggs 

 deposited upon the same day ranged from 4 to 16 days in the length 

 of the egg stage. An examination of the average mean temperature 

 for the various cages shows usually several degrees less mean tem- 

 perature for a long egg stage in comparison with a short egg stage. 



The maximum and minimum temperatures influencing the different 

 lots of eggs are given in Table X. 



