THE PEAR THRIPS. 15 



forms attack their prey externally and literally devour them, while 

 parasitic insects, which are considered perhaps the most important as 

 check insects, must live for a time within the bod^ of their host. 



Our pear thrips, from the very nature of its habits, spending by far 

 the greater part of its life concealed several inches beneath the surface 

 of the ground, as has been shown, is very largely protected from 

 ordinary predaceous or parasitic insects. It comes from the ground so 

 suddenly and injures the trees so quickly that those of its enemies 

 which we have found here can hardly prove an effective check. 



The Raphidians, the commonest feeders on thrips in the Santa Clara 

 Valley, are general predaceous insects, and feed rather on the younger 

 stages of thrips than on the fully developed insects. For the complete 

 control of the thrips pest, they do not appear early enough in the 

 season. Raphidians are distinctly a Western form of insect, being 

 found only in the far West and especially in California; they are 

 unusually voracious, and besides killing almost any insect which happens 

 in their way, they will attack and devour each other if confined together. 



Ants were thoiaght by some to do much good as an enemy to thrips. 

 One gentleman brought in an ant with a thrips impaled in its jaws — 

 the evidence complete. This matter we took up somewhat in detail. 

 Pour hundred ants were taken as they descended the trunk of a thrips- 

 infested tree. Twelve carried something in their jaws; four of these 

 objects were thrips. From the observations only one per cent (four out 

 of four hundred) were actually killing thrips. It may be that others 

 of these ants killed thrips, but did not carry them down the tree. It 

 has been a common observation among orchardists that where ants 

 were usually abundant thrips were not numerous. 



Spiders killed many thrips. Breeding-cages were placed in trees for 

 determining various points in the life habits of thrips, and later almost 

 invariably one or more spiders would be found within and most of the 

 thrips gone. 



The most effective natural enemy of thrips in the Eastern States is a 

 bug, Triphleps insidiosus Say, as mentioned by Dr. Hinds; it feeds on 

 both plants and insects, and at times may be quite as destructive as the 

 thrips itself. 



It was noticed by both myself and Mr. Budlong that often a tree 

 would be thickly infested with young thrips and when these disappeared, 

 supposedly going into the ground, only a few could be found; they 

 seemed also to leave the tree before reaching full growth. We believe the 

 explanation for this is that a fungous disease thinned out their number 

 ■ to quite a large extent. This is borne out by the fact that some dead 

 thrips were found whose bodies were penetrated by a fungus mycelium, 

 and in one case small sporangia were seen on tiny stalks projecting 

 from the body. It is possible that these insects were dead before being 

 attacked by the fungus, and that after all the fungus was not parasitic. 



