DESTRUCTION OF INSECTS BY FUNGI. 47 



forests of Pomerania and Posen the caterpillars have been 

 killed by Empnxa aulicw in such quantities as to have 

 saved the trees from total destruction. These Entomoph- 

 thora forms are difficult to cultivate artificially, but in 1881 

 Brefeld cultivated them in sterilized veal soup, and pre- 

 viously he experimented with the conidia of Entomoplitliora 

 radicans (Fig. 40), applying them to 120 cabbage cater- 

 pillars, with the result that 81 speedily died of the fungus 

 disease resulting. But the most hopeful results, Forbes 

 thinks, from the artificial cultivation of vegetable insecti- 

 cides will attend the use of the muscardine fungi (Botrytis, 

 Isaria, and Cordyceps), since their spores and conidia "have 

 germinated freely again and again in sweetened water, in 

 sterilized beer-mash, in solutions of gelatine and of gum, 

 and may even grow to some extent in pure water. In 

 these the Botrytis stage arises, and may form its spherical 

 conidia in vast abundance; and these have been used with 

 perfect success for the infection of healthy insects in great 

 variety." 



The question has been asked: Cannot we propagate the 

 bacterial insect-diseases and utilize them as destructive 

 agents against insect-pests? Metschnikoff has. suggested 

 the feasibility of the cultivation of insect-bacteria, and the 

 application of the cultivated" fungus in quantity to places 

 infested by these insects; and several years previously the 

 famous experimenter, Pasteur, recommended to the French 

 Phylloxera Commission to find a means of destroying the 

 Phylloxera by inoculation with a microscopic fungus. 

 Balbiani finds that certain Bacilli when inoculated in the 

 blood of other insects kill them. Deatb follows in from 

 twelve to forty-eight hours, according to external tempera- 

 ture, the number and origin of spores, and the size, age, 

 and susceptibility of the subject. They die with all of the 

 symptoms which characterize flacherie in silk-worms. 



The practical difficulty in experiments in this direction 

 appears to be that, though the air is more or less filled with 

 floating disease-germs, insects like other animals, and man 



