MICROBIOLOGY OF DISEASES OF INSECTS 63 S 



time loosening and breaking off at the point of infection. Within 

 certain limits neither the size nor the number of infected areas seems to 

 affect the activity of the grub. Most grubs are very active unless badly 

 infected with the disease. 



Causal Organism. — Pure cultures of M. nigrofaciens show micrococci of vary- 

 ing sizes, o.Qju and 1.2/t to i.4ju diameter with dividing forms; occur singly, in pairs, 

 threes (triangular), fours (tetrads or diamond shape), and dumps of more or less 

 regular groupings, the individuals in, a group arranged in a honeycomb-like order; 

 chains of more than three never observed. Gram-positive; stains well with anilin 

 dyes. 



Growth on agar abundant, beaded, flat, glistening, opaque, pale orange yellow, 

 butyrous consistency, no odor. Cultures newly isolated are not pigmented and give 

 only a moderate growth. Turbidity in broth, no ring or pellicle, no gas. - Litmus 

 milk is slightly reduced and acidified, no curd, yellowish deposit of bacterial cells. 

 Gelatin is liquefied; dextrose, lactose and saccharose not fermented. Moderate 

 indol production; nitrates reduced. 



Methods of Infection. — Sterilized soil was inoculated Tvith a 

 broth culture of the micrococcus and in the soil were placed apparently 

 uninfected larvae, which were incised to imitate accidental abrasion. 

 Characteristic lesions developed in two days at these points. Under 

 natural conditions these larvae bite one another, especially if they are 

 very numerous in any one place; this may account for the rapid spread 

 of the disease. M. nigrofaciens must be a common soil organism, espe- 

 cially where this disease is common. Parasitic insects or fungi may 

 also aid in making infection possible. 



Excessively wet soil favors the progress of the disease. Larvae of 

 Allorhina nitida, the southern June beetle, are susceptible to this infec- 

 tion but less so than the Lachnosferna spp. The American cockroach, 

 Periplaneta americana, is also slightly susceptible, the infection limitintg 

 itself to the legs. 



M. nigrofaciens does not lend itself readily to the control of the 

 white grubs on account of the limiting environmental conditions. 



Flacherie, an Infectious Disease of Silk-worms 



Streptococcus bombycis — Cohn 



History and Distribution. — Flacherie appeared in the silk indus- 

 try as an epidemic at the end of the sixteenth century. It was again 

 a serious epidemic about the year 1869 in the silk nurseries of southern 



