THE PEAR THRIPS. 13 
| ~ may be found within 2 or 3 inches of the surface. Thrips are entering 
the ground mostly during 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 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 helpful. A certain row of cherry trees which was 
_ badly infested with thrips during 1905 was kept under constant obser- 
~ yation for several months because it represented various interesting 
= 4 pele SS ereY ft 
conditions. The trees bordered 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, which, though uncultivated, 
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 larve by thousands matured, dropped 
down, and entered the ground. These larve 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 werescattered about generally, 
regardless of cultivation, except that the many individuals which 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, while in the well-cultivated soil they were often found 6 or 7 
, - inches below the ground surface. They could be found easily any- 
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 aninch 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 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., 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 thrips, 
in that the insect is left undisturbed during almost the entire period 
occupied by the resting stage—from June until the following February. 
