168 Maine Agricultural Experiment Station. 1918. 



and are to a slight extent gregarious. They are very sluggish, and their 

 comparatively soft bodies are covered with their powdery excreta. The 

 work of the larvae is illustrated in figure 13B. 



The Prepupa. 



Formation of the pupa cell. In all insects which undergo 

 a complete metamorphosis, the wings are developed internally 

 in the larva as hypodermal invaginations. Soon a part of this 

 invagination evaginates to form the wing-bud proper, and just 

 before the formation of the pupal cuticula, this wing-bud pushes 

 out so as to lie on the outside of the hypodermis. The internal 

 wing-bud of the larva is therefore external in the pupa, because 

 it lay outside the hypodermis when the pupa cuticula was se- 

 creted. The period from the outpushing of the wing-bud in thej 

 larva until the molt to the pupa, is spoken of as the prepupal 

 period. 



In flea-beetles generally, the prepupal period is passed in thei 

 earth. As soon as the larva is fully fed, it enters the ground to 

 complete its transformations. Sections of specimens of several 

 different species fixed at this time show clearly that the entrance 

 into the soil closely corresponds with the outpushing of the wing- 

 buds. 



The larvae enter any fairly loose soil, pupating about an 

 inch below the surface. Here they construct a rude ceil by con- 

 tortions of the body, and the earth lining it is cemented together 

 by a mucous secretion, probably poured out by the maxillary 

 glands. (Labial glands, the ordinary salivary glands of insects 

 are wanting in the flea-beetles, as in Coleoptera generally.) The 

 earlier prepupa is straight, and can walk, but by the third day, 

 the body is strongly arcuate, and the insect is unable to move! 

 its legs, due to the degeneration of the larval muscles. 



Color changes of the prepupa. For about two days after! 

 entering the soil, the prepupae become darker in color, but then 

 they become lighter, and by the fourth day are almost white. 



The Pupa. 



The molt from the prepupa to the pupa. This molt is ac- 

 complished in the same way in all of the flea-beetles studied, and 

 is described in detail under the elm flea-beetle (page 190). 



