148 MICROSCOPIC ANIMAL FORMS AS ANTAGONISTS 



couragedj (c) microbial agents infectious to plants, animals, and man 

 that are spread by insects. 



Various bacterial diseases that formerly caused considerable destruc- 

 tion of silkworms and bees have been controlled, once the nature of the 

 organisms concerned was established. One of Pasteur's important con- 

 tributions to microbiology was the control of Flacheria among silk- 

 worms. However, most of the problems of control of injurious insects 

 have been difficult to solve. A great number of bacterial, fungus, and 

 virus diseases of insects are now known, but the many attempts to em- 

 ploy these pathogens in combating the insect hosts have not always been 

 successful. The investigations so far carried out in this important field 

 may be considered as at a very primitive stage. 



Metalnikoff (596) compared the bacterial treatment of caterpillars 

 of Pectinofhora gossyfiella with the action of arsenical poisoning. The 

 dry spores of Bacterium efhestiae. Bacterium gelechiae^ Bacterium^ 5, 

 and Bacterium cazaubon, in powder form, were mixed with water at the 

 rate of i to 4 ounces to 2>4 gallons of water, with the addition of 4 per 

 cent of molasses; this preparation was sprayed on the plants two to four 

 times, at regular intervals, at the rate of 196 gallons or less per acre. 

 The best results were obtained for plants treated with B. efhestiae^ the 

 infestation being reduced by about 50 per cent as compared with the 

 controls. A slightly smaller reduction occurred on plots sprayed with 

 B. cazaubofiy while B. gelechiae reduced the infestation by less than 40 

 per cent. Those plants that were treated with the arsenical spray showed 

 a reduction of only 1 8 per cent. 



Recently microorganisms have been used for the control of the larvae 

 of Japanese and other beetles in the soil. A variety of bacteria, fungi, 

 and nematodes were found capable of destroying these larvae. Once the 

 attacking microorganisms have become established in the soil, the larvae 

 and the beetles themselves tend to disappear. Glaser (327) utilized for 

 this purpose Neoaflectana glaseri. This parasite possesses great repro- 

 ductive capacity and is capable of destroying large numbers of grubs. 

 Glaser demonstrated the presence of this nematode also in localities 

 where the grub was not present. 



Fungi have also been utilized for the control of insects. Sweetman 

 (867) emphasized the importance of entomogenous fungi as destructive 



