Minnesota Plant Diseases. 



FIG. 47. An insect 

 mold. (Fly chol- 

 era fungus.) 1. A 

 cluster of threads 

 with spores cling- 

 ing to hairs on 

 the insect's body. 

 2. Fungus threads 

 from the fat-body 

 of an insect. 3. 

 Spore -bearing 

 threads, highly 

 m a g n i fi e d. 4. 

 Above, a single 

 spore; below, 

 germinating spore, 

 forming a sec- 

 ondary spore. 

 Highly magnified. 

 After Brefeld. 



are sent into the threads of the host plant 

 where they obtain nourishment for the para- 

 site. They are also found on certain of the 

 blue-mold group of fungi. 



Insect molds (Entomophthorinece). Of all 

 the algal fungi these are most clearly non- 

 aquatic in their habits. Like the black molds 

 they form breeding spores, from similar sex 

 organs, though these spores are not of fre- 

 quent occurrence. On the other hand the 

 non-sexual spores are very abundant and 

 are pinched off from the ends of special 

 threads. Moreover, there is usually some de- 

 vice for throwing the spore to a distance. 

 The thread is swollen just below the spore 

 and when the latter separates from the thread 

 the release of pressure in the swollen portion 

 results in the forcible ejection of the spore. 

 This is the case in the common fly cholera 

 fungus. Most of the insect molds are para- 

 sites on insects either in the adult stage, as 

 in the fly cholera, or on the larva. 



When the fungus has gained entrance to 

 the body of the insect it soon kills the 

 latter and then lives saprophytically, pro- 

 ducing a great abundance of spores. House 

 flies are commonly attacked by fly cholera in 

 autumn and when they die cling tightly to 

 window panes and other objects. They are 

 soon surrounded by a halo of spores thrown 

 onto the pane from the fungus threads by 

 means of the spore-throwing device described 

 above. Many other insect diseases are 

 caused by these fungi. Caterpillars some- 

 times become covered with moldy growths 

 which completely envelop them. From the 

 surface of these growths are thrown the 

 fungus spores. These parasites of insects 

 prove of great benefit to plant growers 



