50 OUR SHADE TREES AND THEIR INSECT DEFOLIATORS. 



vigor enough to transform into pupae; later the fungus grew, and, press, 

 ing the chitinous portion of the pupa apart, forced its way to the air 

 to fructify. 



"Plants not usually eaten by the caterpillars, as well as others not 

 eaten at all, have upon them the largest numbers of caterpillars killed 

 by the fungus, provided that they grow in the vicinity of suitable 

 food-plants. Perhaps unsuitable food, predisposing tbe caterpillars for 

 any disease, is one of the causes of the innumerable host killed by this 

 fungus, 



"The white cocoons of a parasite {Apanteles hyphantrice Riley) of 

 this caterpillar were in some cases observed to be covered with similar 

 spores of a fungus. Opening such cocoons it was seen that the spores 

 were not simply blown upon the silk and there retained, but that 

 they came from the victim within, and had forced their way through 

 the very dense silken covering." 



Experiments to obtain percentage of diseased caterpillars. 



Experiment I: 



One hundred and twenty-five nearly grown caterpillars were gath- 

 ered (October 7, 1886) at random in one of our public parks. 

 They were imprisoned in large glass jars and daily supplied 

 with suitable food. 

 Eesult, October 18, 1886: 



11 apparently healthy pupae. 

 3 deformed pupae. 



18 yellow cocoons of Meteor us hyphantrice, 

 9 dead pupae, killed by fungus or otherwise. 

 84 dead caterpillars, killed by fungus or otherwise. 



125 



In the earth of the jar were found 17 pupae of Tachina flies, leaving 

 67 caterpillars and 9 pupae killed by the fungus, or 61 per cent. 



Experiment II: 



One hundred and- twenty-five nearly grown caterpillars were gath- 

 ered (October 7, 1886) from a trunk of a Soft Maple tree (un- 

 suitable food) and treated as above. 

 Result, October 18, 1886 : 



8 apparently healthy pupae. 



1 deformed pupa. 



7 yellow cocoons of Meteor us hyphantrice. 

 3 dead pupae, killed by fungus or otherwise. 

 104 dead caterpillars, killed by fungus or otherwise.. 



2 cocoons containing Tachina larvae. 



125 



