THE PEAR THRIPS AND ITS CONTROL. 61 
the others, which then go deeper. Continuous cultivation in June 
and July, which, however, is not always practicable, would also have 
the same effect. It should be remembered that these insects are so 
small that they can easily remain inside of very small clods and be 
turned over and over again by cultivation without receiving any injury. 
The thrips are passing through their pupal development in the 
late fall and early winter, and they are then more susceptible to 
mechanical injury than at any other time. They are only slightly 
active, and can not build other cells if once they are forced from the 
old ones. Their new legs, antenne, and wings are sheathed in long, 
delicate sacs, any one of which may easily be broken or deformed by 
the least disturbance. 
Several experiments with fall and winter plowing for thrips were 
carried out in the fall of 1908, and the following records show what 
results have been obtained in two of these orchards, where special 
attention was given to securing data. Areas of 20 and 70 acres, 
respectively, were plowed and harrowed, and all of the first, with 20 
acres of the second, was cross plowed. This plowing was done 
mostly during December, a lack of early rains having hindered from 
doing the work sooner. In each case several samples of soil, 17 by 
17 inches square by 20 inches deep, were removed from the orchards, 
both before and after treatment, brought to the laboratory yard, 
and embedded to their natural depth in the ground. The cages 
remained open until a time when the adult thrips began to come out. 
They were then covered over, and thereafter a daily record of the 
emerging insects was made for each. The blocks of soil were selected 
from near-by trees and under like conditions, to insure as far as pos- 
sible a uniform number of thrips in each. 
Cages I, IT, III, and IV from the Landon orchard were taken from 
land which had been plowed and cross plowed in November and 
December, and cages V and VI, from the same orchard, were taken 
from under trees where no winter plowing had been done. Cages VII 
and VIII, from the Hume orchard, were taken from land which was 
plowed and cross plowed, and cages TX and X from untreated soil. 
Tasie IIT.—Experiments with fall and winter plowing for the pear thrips in two orchards 
in the Santa Clara Valley, California. 
LANDON ORCHARD. 
Plowed and cross plowed. Not treated. 
Cage III. | Cage IV.| Cage V. | Cage VI. 
Cage I. | Cage II. 
Totalinumberiof thripss=-< 2-2 956-2026. eee | 475 389 
607 115 ans 63) 1,474 
Total number of thrips per square foot of | 
SUTrfACe: a). Sess RAR aher dN Ade Qa, a. | 237 194 | 303 57 587 734 
Average number of thrips per cage: 
Cages TALL, Svein ces sts ae aoa ae alae cS eee NEE) wera eee ON DO 1 bs Ye 396 
WaresiVs and Villette mecepe ete Sere aca ae nate Teme ee emi a es. rm 1,324 
Average number of thrips per square foot of surface in each cage: 
TNNCEN iis Ee a ie eee eae meee Ge eee Sig ii a Se Ae ae eee PePat wSactaseceseen 198 
LU) She Rota BR Re ROO ASE Ghose cag Geen AIR tee Sin ae ere gn ee ne 662 
Percentage living in treated areas as against the numbers of thrips in untreated STOUNC ee eee ee 30 
