THE PEAR THKIPR. 13 



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

 the ground mostly (hiring the hist two weeks of March and (hiring 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 only 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 helpfid. 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 l)or(lered a roadway and were for this reason 

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

 wide extending on either side of the row, wliich, though uncultivated, 

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

 the trees in cjuestion were ver}^ badly infested, were stripped of all 

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

 Many eggs were deposited and larva? by thousands matured, dropped 

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

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

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

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

 regardless of cultivation, exce])t that the many individuals wliich were 

 unable to penetrate the 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, wliile in the well-cultivated soil they were often found 6 or 7 

 inches below the ground surface. They could be found easih^ ai\y- 

 where, 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 they were as common as ever in the 

 uncultivated ground. A dozen or more thrips 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 yards of ground can harbor a very large number 

 of tlmps. 



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., which can be cultivated only 

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

 soils — adobe and clays — can be cultivated only 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 tlirips, 

 in that the insect is left undisturbed durhig ahnost the entire period 

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



