INSECTS IN RELATION TO PLANTS 



201 



Sporotrichum, a genus of hyphomycetous fungi, affects a great variety 

 of insects, spreading within the body of the host and at length emerging 

 to form on the body of the insect a dense white felt-like covering, this 

 consisting chiefly of myriads of spores, by means of which healthy in- 

 sects may become infected. Under favorable conditions, especially in 

 moist seasons, contagious fungus diseases constitute one of The most 

 important checks upon the increase of insects and are therefore of vast 

 economic importance. Thus the termination (in 1889) of a disastrous 

 outbreak of the chinch bug in Illinois and neighboring states "was ap- 

 parently due chiefly, if not altogether, to parasitism by fungi." Arti- 



FIG. 252. Empusa m-itsca, the common fly-fungus. A, house fly (Musca domestica), sur- 

 rounded by fungus spores (conidia); B, group of conidiophores showing conidia in several 

 stages of development; C, basidium (b) bearing conidium (c) before f discharge. B and C 

 after THAXTER. 



ficial cultures of the common Sporotrichum globuliferum have been used 

 extensively as a means of spreading infection among chinch bugs and 

 grasshoppers, with, however, but moderate success as yet. 



Insects in Relation to Flowers. Among the most marvelous 

 phenomena known to the biologist are the innumerable and complex 

 adaptations by means of which flowers secure cross pollination through 

 the agency of insect visitors. Cross fertilization is actually a necessity 

 for the continued vigor and fertility of flowering plants, and while some 

 of them are adapted for cross pollination by wind or water, the majority 

 of flowering plants exhibit profound modifications of floral structure for 

 compelling insects (and a few other animals, as birds or snails) to carry 



