160 MICROSCOPIC ANIMAL FORMS AS ANTAGONISTS 



ploy these pathogens in combating the insect hosts have not alwaj's been 

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

 may be considered as at a very primitive stage. 



Metalnikoff (634) compared the bacterial treatment of caterpillars 

 of Pect'mophora gossypiella with the action of arsenical poisoning. The 

 dry spores of Bacterhrrn efhest'iae, Bacterium gelechiaey Bacterium 5, 

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

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

 cent of molasses J this preparation was sprayed on the plants t^^'o 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. ephestiaej the 

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

 controls. A slightly smaller reduction occurred on plots sprayed with 

 B. cazauborij 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 18 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 destro\-ing these larvae. Once the 

 attacking microorganisms have become established in the soil, the larvae 

 and the beetles themselves tend to disappear. Glaser {'^2)5) utilized for 

 this purpose Neoaflectana glaseri. This parasite possesses great repro- 

 ductive capacity and is capable of destro}-ing large numbers of grubs. 

 Glaser demonstrated the presence of this nematode also in localities 

 where the grub was not present. 



Dutk\' (222) described two spore-forming bacteria {Bacillus fo- 

 filUae and Bacillus lentimorbus) which cause the milky disease of the 

 larvae of the Japanese beetle. These bacteria are grown in the larvae 

 and then inoculated into soil. They are capable of infecting the grub, 

 and are said to be responsible for the reduction in the beetle population. 

 Bacteria pathogenic to the citrus red scale have also been isolated from 

 the soil (868). 



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

 (891 ) emphasized the importance of entomogenous fungi as destructive 

 enemies of insects. A limitation to their practical importance in the fight 

 against insects is that the fungi require special conditions for develop- 



