THE PEAR THRIPS. 



15 



Lind.) . Botli tlie tliri|)s and the mite were •'^ery common in large onion 

 fields, covering several hundred acres. A mite would be seen to ap- 

 proach and grasp a tlirips with its front pair of legs and, inserting its 

 proboscis, suck out the body juices of its prey. A single mite was 

 often observed thus to kill several thrips within a very few minutes. 

 The writer strongly suspects that some mite preys on the younger 

 stages of the pear tlirips wliile it is in the ground. This would be 

 entirely possible, and mites are commonly found in the grass and in 

 the ground. 



A fungus, presumably parasitic, has been endemic among thrips 

 during the seasons 1005 and 1906. In its difl'erent stages it lives 

 on both young and mature thrips, and in a way parallels the life of its 

 host. During the spring of 1905 thrips larva^ were often observed to 

 be thickly infesting a tree, and after these had disappeared, presum- 

 ably having gone into the ground, none or but few living ones could 

 be found. Many larvae, too, seemed to 

 leave the tree before they li:i 1 reached 

 full growth, and within breeding cages 

 these larvae were seen to die as the 

 direct result of the parasite. Project- 

 ing from their bodies were to be seen 

 the tiny fruiting conidiophores of the 

 fungus. Adult thrips were seen to be 

 attacked by another form of the para- 

 site during the spring of 1906. The 

 past two seasons have offered almost 

 ideal conditions for the development 

 of the fungus, enabling it to become 

 quite widespread. 



The life histor3' of the fungus has 

 been determined only in part. The 

 heavy-walled resting spores, the dor- 

 mant stage, are found within larvie and adults in the ground; never, 

 thus far, in pu])9e in the ground or in individuals on the tree. Dead 

 larvae from the ground show that the internal body organs have all 

 been displaced by the fungus, and in most cases the body contains 

 only a mass of the heayv^-walled spores. The transition which takes 

 place in the formation of these spores is as yet not clear, but there 

 seems to be a general breaking up of the fungus hyphx within the 

 thrips' body. In one well-prepared specimen there was an indistinct 

 grouping of particles around many centers. These were presumably 

 the forming spores, for in the next stage the formation of such si)ores 

 was complete. These heavy-walled spores may be found nearly the 

 whole year through, although they are especially abundant from May 

 until the following February. 



Fig. S.— a, Resting spores of a fungus 

 found within dead thrips larva, much 

 enlarged; b, same spores, highly mag- 

 nified. (Original.) 



