14 THE PEAK THKIPS. 



quiescent until the following year. Thrips get down into the ground 

 from three to ten inches, according to the structure and condition of 

 the-soil; the prevailing depth is four to five inches. They are scattered 

 generally from a few inches to several feet from the trunk of the 

 tree. At the present time (September 30th), though the insects have 

 been in the ground several months, they are still active if disturbed 

 and do not show signs of wing formation, the first indication of the 

 approaching nymph. Insects taken from the ground on August 28th 

 still showed green matter (chlorophyll) within the digestive tract, pre- 

 sumably food taken in several months before but as yet undigested. 



The pupal changes take place in the ground in the same cell where 

 the larva has spent so much of its time. We have not determined how 

 long this stage lasts. 



Orchardists know the adult insect best. It is the adult which comes 

 to our trees in countless numbers and which does the greatest injury to 

 fruit buds and blossoms. The mature insect, having wings, flies up 

 from the ground to the tree and, if it finds the tree in suitable con- 

 ^ dition, at once begins to feed; but if it does not find the proper conditions, 

 it moves on to other and better places. Thrips remain close during the 

 day, either feeding or depositing eggs. They often leave the food-plants 

 just before sundown, and it is especially at this time that they migrate 

 from place to place. We have distinguished two modes of flight: a 

 hovering and a migrating one. If the food-plant offers suitable food 

 the insect comes out for a few minutes, hovers around and a little later 

 settles back on the same or a nearby tree. There is, however, a dis- 

 tinctly migratory flight, when the insects in great numbers fly for some 

 distance, and in this way they are spread over a large area. 



Adult thrips appeared in many orchards in alarming numbers on 

 February 22d during the season of 1905, and in 1904 some two or three 

 days earlier than this. Thrips continued to come out from the ground 

 on through March and April and for a short time during May. On 

 May 5th pupal forms were taken from the soil, and if, as we think, the 

 insect is but single-brooded, all of the previous year's forms had not 

 matured at this time. 



METHODS OF CONTROL. 



Natural Enemies. — The subject of natural enemies for the controlling 

 of our insect pests is of prime importance. If the pear thrips has an 

 effective natural enemy, what is it? And if it is not present here, 

 where can it be found? Such questions come to us repeatedly. First 

 of all wc must know as much as possible about the life habits of the 

 thrips itself, and this is what we have tried to present in this report. 

 Up to the present time we have found several common predaceous 

 insects feeding on thrips, but none which are parasitic. Predaceous 



