482 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 



an epidemic form throughout the entire summer and naturally many 

 caterpillars escape since infection can probably only take place through 

 the mouth by means of the food. Dead caterpillars disintegrate and 

 their fluids soil the leaves, and other caterpillars on eating these be- 

 come infected. Some experiments, to be mentioned later, seemed to 

 show that this is the only way infection can occur. It at once becomes 

 apparent why the disease plays such havoc in a heavily infested 

 locality. 



After being collected from a certain place some of the caterpillars 

 were isolated in separate autoclaved boxes and placed in rooms which 

 had never been used for this purpose. Others were kept together in 

 what were known as sitock boxes. Since it has, we believe, been 

 accepted that unfavorable conditions assist the development of the 

 disease, provided infection has occurred, the individuals in the differ- 

 ent stock boxes were treated in a variety of ways. Some were starved, 

 others were subjected to the heat of the sun, still others were fed with 

 leaves soaked in water for forty-eight hours. After several days in case 

 no disease appeared in either the isolated boxes or in those thus treated, 

 it was thought safe to use them for the experiments. Several times 

 during such health tests one or more caterpillars would contract the 

 disease and then the entire collection was thrown away, the boxes 

 were again autoclaved, and another lot brought in to be submitted to a 

 similar physical examination. Such a method of obtaining healthy 

 individuals proves to be much more satisfactory than the blood test 

 as our controls show and if large enough numbers are used is perfectly 

 safe. It was only owing to the large series of experiments which we 

 performed as will be seen from our next publication that we were able 

 to come to any conclusions at all concerning the virus of the wilt 

 disease. 



Exciting Agents Thought to Be Responsible for the Disease 



A disease very similar to the wilt disease of the gipsy moth is known 

 to attack the silkworm and the nun moth in Germany. In this coun- 

 try we have another similar disease in our two species of tent cater- 

 pillars, Malacosoma dissiria and M. americana. 



In Europe there is a tendency to group all of the caterpillar diseases 

 which are characterized by the formation of polyhedral bodies under 

 the name of "polyederkrankheit" or polyhedral diseases. This is 

 an excellent way to distinguish them from those diseases not char- 

 acterized by the formation of such bodies for, though we do not believe 

 that the polyhedral bodies are the exciting cause of the disease, we are 

 convinced, nevertheless, that they are absolutely specific for a certain 

 type of malady. 



