INSECT DISEASES AND MICROBIAL CONTROL 149 



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

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

 ment, especially high humidity and favorable temperature, which are 

 not always found under natural conditions. 



Dutky (219) described two spore-forming bacteria {Bacillus fo- 

 filliae 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 (840). 



Glasgow (328) established that some of the caecal bacteria of Het- 

 eroptera show a marked antagonism toward other bacteria and proto- 

 zoan parasites that occur in the intestines of these insects. The caecal 

 system of the insects was removed and dropped into nutrient bouillon, 

 where it remained for a month or more without showing any bacterial 

 growth. This was believed to be proof of the fact that the caecal bac- 

 teria are antagonistic to ordinary saprophytic and parasitic bacteria and 

 prevent their development j also they apparently kill these bacteria 

 when they invade the alimentary canal of the insect. 



According to Duncan (215), the bactericidal principle found in dif- 

 ferent insects and ticks shows differences in regard to the types of bac- 

 teria affected and the degree of their susceptibility. The gut-contents 

 of Argas and Stomoxys show the widest range of action j that of bugs, 

 the least. Spore-forming bacteria are especially affected by material 

 from Stomoxys J whereas staphylococci appear to be more susceptible to 

 the action of Argas material. The gut-contents of ticks was found to 

 have a v/eak activity upon P. festis, whereas the contents of certain in- 

 sects favored the growth of the latter. This phenomenon may have a 

 bearing upon the function of the plague flea. The action of the lethal 

 principle is greater and more rapid at 37° C. than at room temperature. 

 The lethal principle has been found to be active for at least six months 

 when kept in a dry state. It is thermostable, resisting temperatures as 

 high as 120° C, and is not destroyed by proteolytic enzymes. It appears 

 to be bound to proteins, since it is precipitated from solution by alcohol 

 and acetone, but it is not affected by these reagents. It is insoluble in the 



