906 MICROBIAL DISEASES OF INSECTS 



diseases. This succession of diseases among insects takes place with 

 such periodicity that those who are most intimately connected with 

 their study, can predict very closely both the duration of the epizootic 

 in progress and the time intervening before the onset of the next one* 

 This same periodicity takes place more or less among the more highly 

 organized animals but the "explosive" character is greatly modified 

 by the length of the life cycle. 



BACTERIAL DISEASE or JUNE BEETLE LARVAE, Lachno sterna spp. 



Micrococcus nigrofaciens Nor thrup * 



HISTORY AND DISTRIBUTION. The characteristics of this disease 

 were noted in 1893 by Krassilstschik, Russia, but he did not consider 

 it a disease. It is common everywhere in the United States that 

 white grubs of this and related species are found; infected specimens 

 have also been received from Porto Rico. 



SYMPTOMS. The normal larva is white, quite firm, covered with 

 conspicuous hairs; the head is brown as are also the spiracles or breath- 

 ing pores along either side. The diseased larva has black shiny spots, 

 sharply circumscribed, located mainly along the joints of the legs, 

 spiracles, and upon the dorsal or ventral segments of the white portion. 



Badly diseased larvae are almost entirely black or brownish black 

 in color; the whole body often seems to be in a state of advanced putre- 

 faction, yet the larva still shows life. 



The progressive destructiveness of the disease is most marked in 

 the affections of the legs. In some cases the infection begins at the tip 

 of the leg and as it progresses, the leg, segment by segment, blackens 

 and drops off, leaving the stumps shiny, black, and sometimes swollen 

 in appearance; in other cases the infection occurs at one of the inter- 

 mediate joints or at the joint nearest the body of the grub, the leg in 

 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 i.2/* to 1.4^1 diameter with dividing forms; occur singly, in pairs, 

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



* Northrup, Z. A bacterial disease of June beetle larvae, Lachnosterna spp. Tech. Bui. 

 18. Mich Exp. Sta., 1914. 



