ii6 Minnesota Plant Diseases. 



because they destroy so many insect pests of plants, as lice, lo- 

 custs, etc. They are also responsible for some destruction nf 

 such common pests as mosquitos. Some insect molds are sap- 

 rophytes living on dung and are apparently of no economic im- 

 portance. A few attack plants and particularly the sexual 

 plants of ferns when cultivated in greenhouses. They cause a 

 disease similar to damping-ofif. The economic advantages of 

 this group, however, far outweigh the injuries. (Figs. 14, 47.) 



