I02 Journal of Agricultural Research voi. iv, no. 2 



How the wilt of gipsy-moth caterpillars was brought to this country 

 will probably always remain a puzzle, but many possibilities suggest 

 themselves. Wilt and Wipfelkrankheit, a disease of the European nun- 

 moth caterpillars, may be identical, and the disease may have been intro- 

 duced on trees and shrubbery or other material. This is not at all 

 improbable, for when caterpillars die and disintegrate on trees, the virus 

 may dry on them, making it easy for the disease to gain entrance into 

 this country on shipments of plants. This seems very likely in the light 

 of recent investigations by Escherich and Miyajima (4) and Prowazek 

 (12) on the long resistance to drying of the virus of Wipfelkrankheit and 

 Gelbsucht. 



Then, again, wilt may have been introduced from its original source 

 with the parasites in 1905, when the State of Massachusetts, in coop- 

 eration with the Federal Bureau of Entomology, imported large num- 

 bers of parasites and natural enemies of the gipsy moth from its native 

 homes in Europe and Japan. The first definite printed record of the 

 wilt disease is the one given two years later by Howard and Fiske 

 (9). One of the tachinid flies, Compsilura concinnata Meig., in the vari- 

 ous stages of its life history is especially well adapted to aid in the rapid 

 dispersion of the disease. This imported parasite and others which are 

 spreading rapidly may be the cause of the prodigious increase in wilt 

 mortahty since 1907. 



Finally, the wilt of the tent caterpillar and that of the gipsy moth may 

 possibly be identical, and the latter, though not previously affected, for 

 some reason may have become susceptible to the disease of the former. 

 This last theory does not seem very plausible, however, and ought not 

 to be considered seriously till we have experimental proof of the identity 

 of the wilt diseases of the tent caterpillar and gipsy moth. 



DLSTRIBUTION AND EPIDEMIOLOGY OF WILT 



There is every reason to suppose that the wilt is distributed over 

 the entire territory infested by the gipsy moth. In the summer of 

 1 91 3 the writer personally visited places in Maine, New Hampshire, 

 Massachusetts, and Rhode Island during the caterpillar season and 

 found the disease to a greater or less extent in all these States. To be 

 absolutely certain, material was always collected from the points visited 

 and was later examined microscopically for polyhedra (p. 104). The field 

 men of the Bureau of Entomology scattered throughout the area of infesta- 

 tion sent in diseased material from localities which the writer was unable 

 to visit. In this way records of some 112 separate locahties where the 

 disease occurred, including the writer's observ-ations, were obtained. 



At present the gipsy-moth-infested area in Maine embraces about 

 4,850 square miles; in New Hampshire, 4,960 square miles; in Massa- 

 chusetts, 4,975 square miles; and in Rhode Island, 450 square miles. 

 Wilt, based on microscopical examinations, was found in 4 places 



