THE PEAE THRIPS AND ITS CONTROL. 



59 



disturbed, until the fall of the year, when they change to pupae and 

 their wings begin to develop. 



The depth to which these insects penetrate in well-cultivated or- 

 orchards may be noted in the following 

 tables. In the establishment of these rec- 

 ords, blocks of soil 6 by 6 inches square by 

 20 inches deep were removed from under- 

 neath prune and pear trees, brought to 

 the laboratory, and examined in layers, 

 inch by inch, the thrips in each layer being 

 counted. The figures in each case repre- 

 sent the total of all of the samples from 

 each orchard — 6 from the Bogen orchard, 

 10 from the Landon, and 4 each from 

 the Hume and Sorosis orchards. The 

 percentages represent what proportion 

 of the thrips are in the soil above the 

 mentioned depth after which the per- 

 centage figures stand. The loose top soil 

 of about 4 inches contained no thrips. 



Fig. 16.— The pear thrips: Nymph 

 or pupa. Much enlarged. (Au- 

 thor's illustration.) 



Table II. — Proportion of larvse of pear thrips in ground at different depths; records 



from four orchards in the Santa Clara Valley, California. 





>. of layer. 



Depth. 



Depth of larvse in soil. 



N( 



Bogen orchard 

 (6 samples). 



Landon orchard 

 (10 samples). 



Hume orchard 

 (4 samples). 



Sorosis orchard 

 (4 samples). 





No. of 

 thrips. 



Per 

 cent. 



No. of 

 thrips. 



Per 

 cent. 



No. of 



thrips. 



Per 

 cent. 



No. of 

 thrips. 



Per 



cent. 



5 



Inches. 



4 to 5 



5 to 6 



6 to 7 



7 to 8 



8 to 9 

 9 to 10 



10 to 11 



11 to 12 

 . 12 to 13 



13 to 14 



14 to 15 



15 to 16 



3 



29 

 39 

 45 

 71 

 58 

 41 

 26 

 25 

 17 

 12 



4 



""7." 75" 



17.75 



29 



46.75 



61.25 



71.5 



78 



84 



249 

 518 

 829 

 501 

 305 

 168 

 172 

 87 

 21 

 •76 

 33 

 



'"25" 

 54 

 71 



81 



87 



188 



277 



92 



38 



14 



7 



3 



2 



2 



3 



1 







74" 



88 

 94 

 95 



1 



14 



55 



25 



6 



8 



6 

 1 

 

 1 

 





6 



12 



7 



55 



8 



75 



9 



80 



10 





11 





12 





13 





14 





15 





16 







Total numt 



Average nu 



per surfac 



er of larvae, 

 tnber larvae 

 e sq. foot. . . 







370 

 2G6 





2,959 

 1,183 





627 

 627 





126 

 126 





THE PUPA. 



The period of pupation begins in September and reaches its maxi- 

 mum during October, November, and December. The insect is at 

 this time forming its new legs, antennae, and wings, each appendage 

 developing within its own little sac and hanging free at the side of 

 the body (fig. 16). A few prematurely forming pupae have been 



