654 MICROBIAL DISEASES OF INSECTS 



color and assumes at first a slightly yellowish, tint. "Brown" is the 

 most characteristic appearance assumed by the larva during its decay. 

 Various shades are observed. The term "gray" might sometimes 

 appropriately be used to designate it. The form of the larva dead of 

 this disease changes much less than it does in foul brood. The body 

 wall is not easily broken, as a rule. On this account, often the entire 

 larva can be removed from the cell intact. The content of this saclike 

 larva is more or less watery. The head end is usually turned markedly 

 upward. The dried larva or scale is easily removed from the lower 

 side wall. There is practically no odor to the brood combs. 



Causal Organism. — No microorganisms have been found either 

 culturally or microscopically. However, experimental evidence shows 

 that the etiological factor is a filterable virus. 



' Methods of Infection. — ^Larvae, sick and dead of sac brood were 

 picked from the combs, crushed and diluted with sterile water. The 

 suspension was filtered by means of the Berkefeld filter. This filtrate 

 was fed in sirup to healthy colonies with the result that the typical 

 symptoms of the disease were produced in all cases. 



The virus is killed by heating at 60° for ten minutes. 



Wilt Disease or Flacherie of the Gipsy Moth Caterpillar, 



Porthetria dispar L. 



Filterable virus — Glaser* 



History and Distribution. — There is no account of the occurrence 

 of wilt in America prior to 1900. This disease may have been intro- 

 duced on trees or shrubs imported from Europe, in which country 

 "Wipfelkrankheit," a wilt disease of the European nun-moth cater- 

 pillars, Psilura monacha, exists. In Europe flacherie has become the 

 "guardian angel" of the central European forests. 



In the United States there is every reason to suppose that the wilt 

 is distributed over the entire territory infested by the gipsy moth, a 

 territory of about 4,850 square miles (1915) extending over varioiis 

 parts of Maine, New Hampshire, Massachusetts and Rhode Island. 



Symptoms. — The symptoms of the wilt disease of the gipsy moth 



• Glaser, R. W. and Chapman, J. W. The Wilt Disease of the Gipsy Moth Caterpillar. 

 Jour. Econ. Entomol., 6, 1913,'pp. 479-488. 



Reiff, W. The Wilt Disease, or Flacherie, of the Gypsy Moth, 1911. 



