THE PEAR THKIPS. 13 



maybe found within 2 or 3 inches of the surface. Thrips are entering 

 the ground mosth^ (hiring the last two weeks of March and during April, 

 a period when the most active cultivation of the year is carried on. 

 But the insects are very active at this time, and if they are onh^ dis- 

 turbed and not killed in the mechanical stirring of the soil they simply 

 find a new place to hide and perhaps go a little deeper into the ground. 

 From the following evidence, however, it is quite obvious that careful 

 spring cultivation is heli:>fiil. A certain row of cherry trees which was 

 badly infested with thrips during 1905 was kept under constant obser- 

 vation for several months because it represented various interesting 

 conditions. The trees bordered a roadwa}^ and were for this reason 

 cultivated only on one side. There was a strip of lantl perhaps .3 feet 

 wide extending on either side of the row, which, though imcultivated, 

 was not hardened like the roadway. In February and March, 1905, 

 the trees in question were very badly infested, were stripped of all 

 their fruits, and left with pale, ragged leaves. Adults were numerous. 

 Many eggs were deposited and larvtr by thousands matured, dropped 

 down, and entered the ground. These larva> were actually seen enter- 

 ing the soil, mostly during the month of April. During April and 

 May they were readily found in the groimd several feet from the tree 

 as well as near to its trunk. They were scattered about generally, 

 regardless of cultivation,- except that the many individuals which were 

 unal)le to penetrate tho hard gravel road crawled off to the side. They 

 did not go deeper than 3 or 4 inches in the uncultivated strip near the 

 trees, while in the well-cultivated soil they were often found 6 or 7 

 inches below the groimd surface. They could be found easily an}-- 

 wdiere, in April, just after entering the ground. After the spring and 

 early summer cultivating, however, almost none could be found in 

 the deeply cultivated soil, but the}" were as common as ever in the 

 uncultivated ground. A dozen or more tlirips were often collected 

 from a small clod about an inch and a half in diameter. Small uncul- 

 tivated areas may be found in almost any orchard, and it is a fact 

 that a few square 3^ards of ground can harbor a ver}'' large number 

 of thrips. 



Cultivation methods, however, as a means of control, can be only 

 partially effective at best. One can not kill all of the thrips in the 

 ground even with the most careful cultivation, and there are always 

 men who can not or will not cultivate at the proper time. Then, too, 

 there are areas along fences, ditches, etc., wliich can be cultivated onh^ 

 with great difficulty. What is even more important, certain kinds of 

 soils — adobe and claya — can be cultivated onl}" under certain condi- 

 tions to be kept mellow and loose. The present manner of cultivation 

 in the Santa Clara Valley offers almost ideal conditions for the thrips, 

 in that the insect is left undisturbed during almost the entire period 

 occupied by the resting stage — from June until the following February. 



