THE GIPSY MOTH AS A FOREST INSECT. 5 



ARTIFICIAL UTILIZATION OF THE " WILT " DISEASE. 



It seems necessary to emphasize the foregomg statement that the 

 resistance of certain species of trees is directly due to the suscepti- 

 bility of caterpillars, feeding upon the foliage of these trees, to death 

 through the "wilt" disease, and thus incidentally to emphasize the 

 very great importance of the disease itself. Since this disease is 

 believed to result from parasitism by a specific bacterium, the propo- 

 sition of increasing its efficiency tln-ough infecting the caterpillars 

 artificially with cultures of the bacterium at once suggests itself. 



This possibility is largely precluded if equal emphasis be laid upon 

 the real character of the disease, so far as we are able to determine it, 

 either through intensive study of the organism believed to be respon- 

 sible or through observations upon its activities in the field. 



At the present time wherever caterpillars are to be found, infected 

 caterpillars have been found also upon every occasion when search 

 for them has been made. Furthermore, even though the infection 

 were proved to be wmd-borne, as has been contended — and there is 

 room for doubt regarding this most essential fact — every particle of 

 reliable evidence indicates that slightly infected caterpillars remain 

 reasonably healthy. The condition of the caterpillars upon the arti- 

 ficially protected trees along the roadsides in localities where an epi- 

 demic of the disease prevails in the main body of the forest is, or 

 ought to be, sufficient evidence of this. Notwithstanding that these 

 caterpillars are forced to feed upon trees which have been sprayed, 

 and notwithstanding that through artificial suppression alone are 

 they prevented from stripping the trees, those which escape death 

 amid the various dangers by which they are artificially encompassed 

 remain remarkably healthy, and with comparatively rare exceptions 

 there is an increase in numbers of the fresh egg masses each fall over 

 the number which escaped the creosote brush the preceding spring. 



Rather elaborate experiments have been carried on in the past 

 to determine whether the disease could be practically transmitted 

 through infected food, and with one notable exception those who have 

 conducted such experiments have concluded that artificial utilization of 

 the disease in this manner is impracticable. If the writer is not mis- 

 taken it was Dr. Roland Thaxter, of Harvard University, a specialist 

 of high standing upon the vegetable parasites of insects, who was 

 the first actually to experiment along this fine, and who was the first 

 to be convinced of its futihty. In 1908 Dr. Herbert Johnson, work- 

 ing for the State of Massachusetts in cooperation with Harvard 

 University, conducted an elaborate series of field experiments to test 

 this theory, but with no more promising results. 



Further investigation and experimentation were conducted coop- 

 eratively by the State of Massachusetts and Harvard University 



