February, '15] CHAPMAN AND GLASER: WILT DISEASE _ v 147 



angular than others but with, the possible exception of the tent cater- 

 pillars, this is characteristic of individual polyhedra in the same cater- 

 pillars, where the}^ may vary from an almost spherical to a decidedly 

 angular form. 



Another striking fact is the great difference in size between the poly- 

 hedra in the different species studied. (PL 6, figs. 12-14.) Taking 

 the average of five microscopic fields in each species studied, the poly- 

 hedra of the gipsy moth are the largest, measuring in diameter 

 and those of the tussock moth the smallest, measuring 1.64/z in diam- 

 eter. The polyhedra of the other species are intermediate in size. 

 Glaser in his study of the polyhedra of the gipsy moth caterpillars 

 found some measuring as much as 15jjL in diameter, while in the same 

 caterpillar there were mam' measuring 1.5^ and 2^ in diameter with 

 all possible gradations between these two extremes. 



As to the second part of the question, what relation have the poly- 

 hedra to wilt? AYe have previously stated (Dec, 1913) that the 

 polyhedra were reaction products, a view also held by many European 

 investigators. This view we further believe is strengthened by the 

 present study of the polyhedra. 



A further study was made of some polyhedra taken from caterpillars 

 which died in experiments of cross infection. (PI. 6, figs. 9-11.) That 

 is, apple tent caterpillars were fed with gipsy moth wilt and gipsy 

 moth caterpillars were fed with Nun wilt. A number of such infections 

 were tried but the reciprocal infections were not made. Until this is 

 done we cannot express a definite opinion on the results we have ob- 

 tained so far. We present it more to call attention to or to show what 

 might be done in the future in an experimental way, that might give 

 the solution to the problem. 



We wish at this time to thank all those who have in any way aided 

 us in this wwk; especially those who have sent us material from the 

 field. 



Summary and Conclusions 



1. Wilt occurs in many widely different species of insects. 



2. The clinical aspects of wilt are very similar in all the species of 

 caterpillars studied by us. 



3. Wilt first appears in a chronic form, as conditions become more 

 unfavorable it becomes acute, and finally terminates in a general 

 epidemic. 



4. There is a striking similarity in shape between the polyhedra of 

 the different species of caterpillars given in Group A. 



5. The polyhedra in the different species vary greatly in size. 



6. The great difference in size which exists between polyhedra 

 in the same caterpillar tends to strengthen our view that the poly- 

 hedra are reaction bodies. 



