INSECTS IN RELATION TO PLANTS 259 
white powdery ring, or halo. The white intersegmental bands 
are made by threads of the fungus just named, and the white 
halo by countless asexual spores known as conidia, which have 
been forcibly discharged from the swollen threads that bore 
them (Fig. 251) by pressure, resulting probably from the ab- 
sorption of moisture. These spores, ejected in all directions, 
may infect another fly upon contact and produce a growth of 
fungus threads, or hyphe, in its body. The fungus may be 
propagated also by means of resting spores, as found by Thax- 
ter, our authority upon the fungi of insects. 
Empusa aphidis 1s very common on plant lice and is an im- 
portant check upon their multiplication. Aphids killed by this 
fungus are found clinging to their food plant, with the body 
swollen and discolored. Empusa grylli attacks crickets, grass- 
hoppers, caterpillars and other forms. Curiously enough, 
grasshoppers affected by this fungus almost always crawl to 
the top of some plant and die in this conspicuous position. 
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 insects may become in- 
fected. Under favorable conditions, especially in moist sea- 
sons, 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 Hlinois 
and neighboring states “was apparently due chiefly, if not 
altogether, to parasitism by fungi.”’ Artificial cultures of the 
common Sporotrichum globuliferum have been used exten- 
sively 
y 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 marve- 
lous 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. 
