THE PEAK THRIPS IN CALIFORNIA. 



41 



LENGTH OF EGG STAGE. 



Moulton 1 records the length of the egg stage to be approximately 

 four days, but detailed observations during the season of 1910 at San 

 Jose show it to be considerably longer. The length of the egg stage 

 was first ascertained by inclosing twigs with paper bags before thrips 

 emerged so as to get no outside infestation. Later, when thrips were 

 ovipositing in the field, a considerable number of adults were placed 

 in mica chimneys which had been specially constructed to fit over the 

 twigs in such a manner as to give them as nearly natural conditions 

 as possible, and to permit the eggs to remain in living plant tissue 

 because they usually dried out when the twigs were removed from the 

 tree. These chimneys were made by sewing pieces of strong white 

 cloth in the shape of tubes about 5 or 6 inches long and gluing one 

 end of a cloth tube thus made to each end of the mica chimney. 

 When placed upon the tree, ends of the cloth were tied securely 

 around the twig so that no insects could get in from the outside. 

 The thrips kept for oviposition remained in the cages over night and 

 were removed the next day. To make sure that none would remain 

 in to continue ovipositing, new cages were placed on the twigs in each 

 case. Table IX shows the length of the egg stage. 



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



Cage 



Date de- 



Date 



Number 



of eggs 



hatched. 



Length 

 of egg 

 stage. 



Average 

 mean 



Prevailing 



No. 



posited. 



hatched. 



tempera- 

 ture. 



weather. 











Days. 



F. 





I 



Mar. 10 



Mar. 16 



25 



6 



56 



Cloudv. 







17 



6 



7 



57 



Do." 







18 



9 



8 



58 



Do. 







19 



8 



9 



57 



Do. 







20 



3 



10 



57 



Do. 







22 



10 



12 



52 



Do. 







23 



3 



13 



52 



Do. 







24 



1 



14 



52 



Do. 



II 



Mar. 10 



Mar. 16 



13 



6 



56 



Cloudy. 







17 



27 



7 



57 



Do. 







18 



30 



8 



58 



Do. 







19 



35 



9 



57 



Do. 







20 



8 



10 



57 



Do. 



III 



Mar. 10 



Mar. 16 



27 



6 



56 



Cloudy. 







17 



4 



7 



57 



Do. 







18 



9 



8 



58 



Do. 







19 



14 



9 



57 



Do. 







20 



10 



10 



57 



Do. 







22 



4 



12 



52 



Do. 







23 



1 



13 



52 



Do. 







24 



1 



14 



52 



Do. 



IV 



Apr. 7 



Apr. 14 



3 



7 



55 



Clear. 



V 



Mar. 29 



Apr. 5 



1 



7 



56 



Clear. 







8 



1 



10 



56 



Do. 







10 



1 



12 



56 



Do. 



VI 



Mar. 29 



Apr. 7 



2 



9 



56 



Clear. 







9 



4 



11 



56 



Do. 







10 



1 



12 



56 



Do. 







12 



1 



14 



55 



Do. 



1 Op. cit., p. 8. 



