58 



then contain, without doubt, at least partially, the carriers of 

 the disease, which, according to their number and to the con- 

 stitution of the embryo, will kill, early or late, the larva after 

 it has hatched. Thus Flacherie will be carried again through 

 the whole ontogeny of the descendants of those individuals 

 which were originally infected by the disease. In this case the 

 wilt would be hereditary, and it would have by far the greatest 

 possible economic value and benefit. If, however, the " dying 

 off " of several of the embryos is only a consequence of the 

 weak condition of the female adult, which perhaps was slightly 

 infected during the caterpillar stage, then of course the guaranty 

 for the wilt is not yet given for the next generation. Among 

 the hatching caterpillars there will always be a considerable 

 percentage of weak individuals which thus possess from the 

 beginning the necessary predisposition to the disease. If, then, 

 the climatic conditions develop favorably for the disease, these 

 weak caterpillars will be attacked first by the wilt, but as it 

 increases in virulence it will attack the stronger and healthier 

 individuals. If the climatic conditions are less favorable for 

 the natural appearance of Flacherie, we hope the introduction 

 of the artificially developed Flacherie in the respective localities 

 will transmit the disease to the weak caterpillars. Then the 

 disease will operate as though it had appeared naturally. 



The existence of the wilt does not depend upon climatic 

 conditions as soon as the disease is once established. It is true 

 weather conditions will often be of great advantage in spreading 

 the disease, but not likely to be of considerable harm. Hence, 

 Flacherie, even if its nonheredity should be proved, is a factor 

 of great importance to economic entomology. It will be advis- 

 able to work with the wilt against the gypsy moth in large 

 wooded areas of all kinds, and it has the great advantage of 

 cheapness, while the spraying with arsenate of lead or with 

 other poisons is expensive. A very good scheme would be to 

 furnish as many trees as possible with rings of tanglefoot in 

 heavily infested forest districts, and not to kill the caterpillars 

 after they are gathered together under the rings, but to assist 

 in this manner the more rapid spread of the wilt, since the sick 

 and weak individuals thus have a greater possibility of coming 



