THE PEAR THRTPS. 



15 



Lind.) . Both the thrips unci the mite were ^^cry common in hir^je onion 

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

 ])roach and grasp a thrips with its front pair of legs and, insert hig 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 thrips while 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 1905 and 1906. In its different 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 

 l)e tliickly infesting a tree, and after these had disappeared, presum- 

 al)ly having gone into the ground, none or but few living ones could 

 be found. ]\[any larvie, too, seemed to 

 leave the tree before they had reached 

 fidl growth, and within breeding cages 

 these larva^ Avere 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 

 attackeil by another form of the para- 

 site during the spring of 1900 (lig. 7, a). 

 The past two seasons have offered 

 almost ideal conditions for the develop- 

 ment of the fungus, enabling it to be- 

 come quite widespread. 



The life history' of the fungus has 

 been determined only in part. The 

 heavy-walled resting spores, the dor- 

 mant stage, are found within larva> and adults in the grovin<l; never, 

 thus far, in puppp in the ground or in individuals on the tre(\ 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 heavy-walled spores (fig. 8, a, h). The transititm 

 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 In/phu: 

 within the thri]>s" body. In one well-preparetl specimen there was 

 an indistinct grouping of particles around many centers. These were 

 ]M-esumably the forming spores, for in the next stage the formation 

 of such spores was comi)letc. These heavy-walled spores may be 

 found nearly the whole year through, although they are especially 

 abundant from May until the following February. 



Fig. 8. — Cladosporium sp.: a, resting 

 spores within dead thrips larva, much 

 enlarged; b, same spores, highly mag- 

 nifled. (Original.) 



