140 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 8 



A PRELIMINARY LIST OF INSECTS WHICH HAVE WILT, 

 WITH A COMPARATIVE STUDY OF 

 THEIR POLYHEDRAL 



By J. W. Chapman and R. W. Glaser 



I. Description of Wilt 



Although the nature of wilt in the gipsy moth will be thoroughly 

 discussed by Glaser in a paper soon to be published, a restatement 

 of its recognizable characteristics is necessary for a complete under- 

 standing of the discussion which is to follow; also because many 

 persons are of the belief that wilt is peculiar to gipsy moth cater- 

 pillars only. 



Clinical Picture 



The wilt is characterized by the formation in the bodies of infected 

 caterpillars of polyhedral-shaped, highly refractive, angular bodies, 

 which have their origin in the nuclei of the tracheal matrix, h^^po- 

 dermal cells, fat cells and blood corpuscles. Later some of these 

 burst and the poyhedra are set free in the blood. When death 

 results they make up a great part of the saponified body tissues of the 

 caterpillars. The caterpillars hang by their prolegs, become flaccid 

 and their skin disrupts at the slightest touch. An examination imme- 

 diately after death reveals few or no bacteria and no bad odor. The 

 wilt appears in nature in both a chronic and an acute form. If, how- 

 ever, a dead caterpillar, on microscopic examination, shows no pol}^- 

 hedra it does not have wilt, even though all the gross symptoms 

 may be present. 



The point we wish to emphasize is that a consideration of both the 

 external characteristics and the potyhedra is essential to a complete 

 diagnosis of isolated or chronic cases of wilt; because there are a num- 

 ber of diseases of caterpillars, such as fungous, protozoan and possibly 

 bacterial diseases, with which it might easily be confused under such 

 conditions, even by the most experienced. If on the other hand the 

 wilt has reached the epidemic form, it is highly improbable that it 

 could be confused with am^thing else. 



Following this rule of diagnosis we should look for wilt in all forms 

 of insect life; for where it was thought to be rare it has proven to be 

 common and widely distributed as will be seen from the following 

 insects reported to be affected by it. For convenience of discussion 

 and to prevent possible confusion we have divided them into three 

 groups. 



1 Contribution from the Bureau of Entomology in cooperation with the Bussey 

 Institution of Harvard University. (Bussey Institution Xo. 85.) 



