NATURE OF POLYHEDRAL BODIES FOUND IN INSECTS. 369 



III. Noctuidae. 



3. Leucania nnipuncta Halw. 



4. Noctua clandestine, Harris. 



5. Autographa brassicce Riley. 



IV. Lymantridae. 



6. Porthetria dispar L. 



7. Lymantria monacha L. 



8. Orgyia leucostigma S. and A. 

 V. Lasiocampidae. 



9. Malacosoma americamim Fabr. 

 10. Malacosoma disstria Hubn. 



VI. Bombycidae. 



n. Bombyx mori L. 

 VII. Dioptidae. 



12. Phryganidia calif ornica Packard. 

 VIII. Pieridae. 



13. Colias philodice Godart. 



From a perusal of the above list it will be seen that the poly- 

 hedral diseases are very widely distributed and affect some of 

 our most important economic insects. We have estimated that 

 epidemics of polyhedral diseases at certain times kill off from 30 

 to 70 per cent, of some of our most noxious pests. This is 

 especially true, as we have found in connection with our studies 

 on the gipsy moth, tent caterpillars and army worms. The 

 polyhedral diseases contribute much more to the control of 

 certain of our noxious caterpillars than the combined efforts of 

 all their hymenopterous and dipterous parasites. Therefore, 

 we believe that these diseases merit a serious consideration from 

 all points of view. 



THE POLYHEDRAL BODIES. 



Caterpillars dead from wilt are usually found on some elevated 

 place hanging by their prolegs. Dead nun moth caterpillars 

 are found hanging from the very highest branches of a conifer, 

 dead gipsy moth caterpillars are found hanging anywhere on the 

 trunk of a tree or on a branch ; the favorite dying places of the 

 American tent caterpillars being usually in close proximity to 

 the nest on the branches of an apple or cherry tree. The army 



