16 DECIDTTOUS FRUIT INSECTS AND INSECTICIDES. 



In the coiiidiopliore stage on the tree the fungus hyphse break forth 

 in groups from between the body segmen4:s and extend out as long 

 slender threads, which in turn branch and form numerous fruiting 

 organs (fig. 7). This stage of the fimgus has been taken only from 

 adult thrips on the tree and not from the larv*, and it has been 

 found present almost ever^^vhere that the pear thrips has been collected. 



There is no doubt that the fungus spends a part of its life on the tree 

 and a part in the ground, the rapidly fruiting stage among the active 

 thrips and the hea^"3"-walled dormant stage within the hibernating 

 individuals in the ground; but we can only surmise how it is carried 

 from one to the other. The bodies of the larval thrips within the 

 ground are all absorbed by the fimgus and naturally, therefore, the 

 spores must be carried to a new host before they can germinate to 

 any great extent. We have found adult thrips in the ground whose 

 dead bodies contained only a few spores and others which developed 

 some of the external mycelial growth mtliin their cells. If this were 

 often the case, and these individuals in the ground produced fruiting 

 spores as they do on the trees, it would be an easy matter for healthy 

 individuals in coming from the ground to become accidentally infested 

 and to carry the parasite up to the tree where, because of the gre- 

 garious habits of the insect, it would spread rapidly. 



The fungus grows readily in the nutrient agar under ordinary con- 

 ditions and seems to retain its virulence and can be transferred from 

 cultures to the living thrips. The fungus may prove to be a check 

 for the pear thrips, but its effectiveness is uncertain because it is so 

 subject to climatic conditions. 



Mrs. F. W. Patterson, of the Bureau of Plant Industry, Department 

 of Agriculture, has determined this fungus to be a species of Clado- 

 sporium. Although we have not seen any one of the heavy-walled 

 resting spores actually germinate and develop into a colony, 3'et by 

 planting such spores in nutrient agar we have produced a fungus which 

 proves to be the same as that which developed later from spores taken 

 from an infested thrips directly from the open field. Mrs. Patterson 

 notes a difference between the two fungi, which she attributes to the 

 fact that the one is grown on nutrient agar, wliile the second matured 

 on its natural host. She also remarks that "it is extremely doubtful 

 if any species of this genus has been reported as an entomogenous 

 parasite." From our observations, however, it would seem to be a 

 true parasite, although our chain of evidence is not yet complete. 



o 



