Minnesota Plant Diseases. 71 



killed in a year. A caterpillar after infection can still crawl some 

 distance before death overtakes it and thus the scattering of 

 the fungus spores is materially aided, Attempts, made at vari- 

 ous times to utilize this fungus to combat grubs, have met 

 with varying success, but its use has not yet become general. 

 Silkworms frequently suffer from these fungi and the silk 

 growers of Europe have lost enormous sums of money 

 through such epidemics. The beetles are very frequently the 

 hosts of parasitic fungi, especially of the so-called "beetle fungi" 

 which have already been mentioned. The caterpillar fungus 

 and the insect molds are also to be found on the beetle as well 

 as upon the dragon flies and their allies. Ants, though not very 

 frequent hosts, have been known to harbor the caterpillar 

 fungus. 



Diseases of fish and lower vertebrates. If we now consider 

 the vertebrate animals we find also abundant evidence of fun- 

 gus parasitism. One of the most important cases is that of the 

 fishes. Both the mature fish and its eggs may be attacked. 



FIG. 32. Dead minnow with fish mold (probably Saprolegnia thuretii). Original. 



The fungi are the water or fish molds. Thousands of fish are 

 killed off annually by these parasites. They can be seen on 

 any minnow bait, which has died and been kept for several 

 days. A filmy mold gradually covers the whole surface of the 

 minnow. These fish molds are half saprophytes and live ordi- 

 narily upon dead debris in the water. When, however, they 

 come into contact with living fish, they may attack the latter 

 if conditions are favorable. They apparently are unable to 



