56 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 
in the Santa Clara Valley, namely, the Landon, Bogen, Sorosis, and 
Hume orchards. The cages each contained a solid block of earth 
17 by 17 inches square, representing a surface area of 2 square feet 
and a depth of 18 inches, below which thrips have never been found. 
These cages were removed from under prune and pear trees in the 
several orchards, brought to the laboratory yard, and again em- 
bedded in the ground to their usual depth and covered with a special 
cage. A daily record was made of the thrips issuing from each 
cage. 
TaBLe I.—Records of emergence from soil of adult pear thrips from four orchards in the 
Santa Clara Valley, California, spring of 1909. 
Number of thrips in four cages. Number of thrips in four cages. 
Date. | From | From | From | From | Total. Date. From | From | From | From | Total. 
Lan- | Bogen | Sorosis | Hume Lan- | Bogen | Sorosis | Hume 
donor-|  or- or- or- don or- or- or- or- 
chard. | chard. | chard. | chard. chard. | chard. | chard. | chard. 
1909. 1909 
Feb. 15 18 0 0 0 18 || Mar. 11 13 47 128 310 498 
1 0 0 0 0 0 1 12 62 81 183 338 
17 51 0 0 1 52 13 18 101 87 207 313 
18 176 8 4 4 192 14 1 53 70 124 248 
19 160 14 4 14 192 15 3 71 76 129 279 
20 126 17 12 14 169 16 1 59 74 125 259 
21 60 1 0 14 75 17 3 31 36 72 152 
22 84 10 7 18 119 18 1 15 13 13 42 
23 106 5 7 17 135 19 8 12 22 19 61 
24 403 26 50 73 552 20 1 6 3 18 28 
25 301 35 49 74 459 21 0 1 1 0 2 
26 320 25 35 64 444 22 2 0 2 2 6 
27 232 19 28 134 414 23 0 3 3 7 13 
28 372 74 80 255 781 24 0 0 0 3 3 
Mar. 1 340 109 114 218 781 25 0 0 0 2 2 
104 54 92 285 535 26 1 0 1 1 3 
3 300 188 258 553 | 1,299 27 0 0 4 3 7 
4 191 104 115 304 714 28 0 0 0 7 7 
5 37 93 109 269 508 29 0 0 0 0 0 
6 26 34 87 215 362 30 1 1 0 0 2 
7 13 50 60 315 438 31 0 0 0 0 0 
8 9 38 14 158 219 || Apr. 1 0 0 0 3 3 
9 18 89 77 602 776 PY 0 0 0 0 0 
10 18 114 109 256 497 3 0 0 1 0 1 
The first adult thrips were collected on February 15, but a very 
few individuals had been found in blossoms previous to this time. 
On February 18 they were numerous in one of our experiment 
orchards, and by February 25 they were common in all orchards. 
Maximum emergence begins about February 19 and continues until 
about March 16, a period of three and one-half weeks. A few strag- 
gling individuals continued to come out during all the latter part of 
March and a very few even in April. Practically all thrips, however, 
are out of the ground by March 20. 
The emergence period for thrips in orchards in Contra Costa and 
Solano counties seems to be three or four days earlier and this will 
probably hold true also for orchards along the Sacramento River. 
