41 



The local superintendent was intrusted by Mr. Souther with the 

 breeding of caterpillars. On June 24, 1910, I found the wilt in this 

 brood. The same day, with the assistance of the local superintendent, 

 one part of the material was exposed in the locality mentioned. This 

 brood was thoroughly sick, but the " dying off " of the caterpillars had 

 not begun. The bag containing the material was fastened between 

 twigs about 7 feet from the ground. The caterpillars in this locality 

 were at this time half way between the third and fourth molt. 1 



On Oct. 25, 1910, the fresh egg clusters of this locality were esti- 

 mated by the local superintendent and myself. We found that the 

 place contained almost the same numbers of clusters as in the spring 

 of 1910, with the difference, however, that many clusters had the hairy 

 covering only in part. Several clusters completely lacked this covering. 

 It seems that the disease spread very slowly, and that it did not kill 

 many caterpillars but had merely given them a mild form of the dis- 

 ease, which manifested itself later in the manner mentioned, when the 

 females laid their eggs. The 5 clusters which were first found were ex- 

 amined, like those of other localities. The examination gave the fol- 

 lowing interesting results : 



Cluster 1. 



Unfertilized eggs, . . . 2 \ 



Eggs with dead embryos, . 13 ) = 3 ' 97 per cent "> or about 4 P er cent ' 

 Eggs apparently alive, . . 363 =96.03 per cent., or about 96 per cent. 



Total, 



Unfertilized eggs, . 

 Eggs with dead embryos, 

 Eggs apparently alive, . 



Total, 



Unfertilized eggs, . 

 Eggs with dead embryos, 

 Eggs apparently alive, . 



Total, 



Unfertilized eggs, . 

 Eggs with dead embryos, 

 Eggs apparently alive, . 



Total, 



. 378 eggs. 



Cluster 2. 



92 I = ^'^ P er cen *-j or about 19 per cent. 

 . 422 =81.15 per cent., or about 81 per cent. 



. 520 eggs. 



Cluster 3. 



2\ 

 gg } =13.48 per cent., or about 13.5 per cent. 



. 385 =86.52 per cent., or about 86.5 per cent. 

 . 445 eggs. 



Cluster 4. 



123 1 = 20-98 per cent., or about 21 per cent. 

 . 467 =79.02 per cent., or about 79 per cent. 



. 591 eggs. 



1 This experiment was intentionally undertaken with sick caterpillars only, and no dead ones, 

 in order to see what effect the exposure of only sick individuals might have upon the healthy 

 caterpillars in the field. 



