THE PEAR THRIPS AND ITS CONTROL. 59 
disturbed, until the fall of the year, when they change to pupx 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 1¢- 16—The pear thrips: Nymph 
= : é or pupa. Much enlarged. (Au- 
of about 4 inches contained no thrips. thor’s illustration. ) 
TaBLE II.—Proportion of larve of pear thrips in ground at different depths; records 
Jrom four orchards in the Santa Clara Valley, California. 
Depth of larve in soil. 
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. 
| | 
NL et eee SYS i aga | 188 | Sue Le See aes 
29 7. 75 518 25 277 74 14 12 
39 17. 75 829 54 92 88 55 | 55 
45 | 29 501 71 38 25 75 
71 46. 75 305 81 14 95 6 80 
58 61. 25 168 87 (le eee Ble ches 
41 71.5 1? PAREN 2 3B) eetesreiees Ob Awaits 
26 | 78 Si eee AY a A ES G2) oo sae ed 
25 84 Qs |e ae PAM [Ene ee tA eee oe 
Tale cecexecct LOW Kahan Sule ase Ua eases oe 
Cd eee tobi Mees cleats iil eee sees 1G eee 
L6sqeeer hes 15 to 16 Ze Re en (iy Ee ba (Oy RA EN Ogee 
Total number of larve. SHON WARS thx2 EGS NIE eee G27 | sae erie 1 Reo oee 
Average number larvze 
per surface sq. foot. . . ZOO" | Goa | L LSS S-6eeeee Listy a ed oe RDG SS Saas 
= se = —— = J = =e ! a= 
AMSG Sy 124 09 27 
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, antenne, 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 pupe have been 
