THE PEAR THKIPS. 13 



may be found within 2 or 3 inches of the surface. Thrips arc cntermg 

 the ground mostly during the last two weeks of March and during April, 

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

 But the insects are very active at tliis time, and if they are only dis- 

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

 fmd 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 bordered a roadway and were for this reason 

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

 wide extendmg on either side of the row, which, though uncidtivated, 

 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 luimerous. 

 Many eggs were deposited and larvae 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, except that the many individuals wliicli 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. The}' could be found easily any- 

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

 earh' summer cultivating, however, almost none could be fountl in 

 the deeply cultivated soil, but they were as common as ever in the 

 uncidtivated 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 msLY be fountl in almost any orchard, and it is a fact 

 that a few square yards of ground can harbor a very 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 carefid 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 onl}' 

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

 soils— adobe and clays — can be cultivated onl}^ under certaui condi- 

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

 in the Santa Clara Valley ofl'ers almost ideal conditions for the tlu'ips, 

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

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



