7~ 
THE PEAR THRIPS AND ITS CONTROL. 59 
disturbed, until the fall of the year, when they change to pupe 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 9: 16—The pear thrips: Nymph 
of about 4 inches contained no thrips. Sa Pa as aioe 
Tasie II1.—Proportion of larve of pear thrips in ground at different depths; records 
from four orchards in the Santa Clara Valley, California. 
Depth of larve in soil. 
l | 
Bogen orchard | Landon orchard | Hume orchard | Sorosis orchard 
No. of layer. Depth. (6 samples). | (10 samples). (4 samples). | (4 samples). 
No. of | Per | No. of | Per | No. of Per | No.of Per 
thrips. | cent. | thrips. | cent. | thrips. cent. | thrips. cent. 
eS — —— | = = = — a _ = — 
Inches 
Wika ste; aa sais shsiatera= 4to5 Sl ae Sede 2f: 4 I ee USS ee sets It [atest mi 
(158 SR ee ae 5 to 6 29: Eten | 518 25 | 277 74 14 12 
eke Someones: 6 to7 39 iowa 829 54 | 92 88 55 55 
Sete cost a cenies 7to8 45 | 29 501 7Alal 38 94 25 75 
Oe ae em ea 8 to 9 71 46. 75 | 305 81 14 95 6 80 
1 ee eet 9 to 10 Si Olson | 168 87 bid one Si.) xcmaeens 
Vi aoe SoeeeSnoLe 10 to 11 41 | 71.5 | WE |beonaeee 3)! bonscmes f) pe deca8e 
DAES RP Sorte cece ore 11 to 12 26| 78 t/a eee 71S Se Ge Sac Es 
BS eapeenetiems nara 12 to 13 25 | 84 7 Ree oee 2 lel Reece noe 
Ne Re ee io icare 13 to 14 IW |e cbogee MGR Genes shes | 2 seo Op jeacseens 
De Se chicis c cma 14 to 15 12 |-2--2--- Bo era. as 3 if cates Siete ee ais 
NG! Soe ee aaah! 15 to 16 lal be ao Dione 2 ONE Re Ose csscce 
Total number of larve. STOu|Saaceee Paalel}? ee ae P| Beesesce | 126) |oce see 
Average number larve 
per surface sq. foot. . . BOOM Pos ss TGS Su See ee | 627 |225 25 =< 126 sas ctns= 
THE BURA: 
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, antennz, 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 pupx have been 
