THE BIOLOGY OF THE ALDER FLEA-BEETLE. 265 



In the alder flea-beetle, the prepupal period is passed in the 

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

 to complete its transformations. Sections of specimens fixed at 

 this time show clearly that the entrance into the soil closely 

 corresponds with the outpushing of the wing-buds. 



In nature, as Lintner (1887) pointed out, the insects prefer 

 to pupate under the mossy edge of a half-sunken rock, and the 

 majority of the pupae are probably to be found in such situa- 

 tions. But even under natural conditions they will enter any 

 fairly loose soil, pupating about an inch below the surface of the 

 ground. The larvae construct a rude cell by contortions 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 entirely 

 wanting in this species, 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 the legs. 

 This is due to the degeneration of the larval muscles, for, as has 

 been pointed out already, there is no relation between the larval 

 legs and the imaginal legs. The latter are developed as knobs 

 or pads at the bases of the larval legs, and do not project down 

 into them, so that when the larva molts to the pupa, the larval 

 legs are simply hollow shells. 



Color changes of the prepupa. In several species of this 

 genus, there is a distinct prepupal color cycle, the insect first 

 becoming darker and then very much lighter in color. So far as 

 the writer has observed, there is no change in the coloration of 

 the prepupa of the alder flea-beetle. 



THE PUPA. 



The molt fro in the prepupa to the pupa. When the prepupa 

 is ready to molt to the pupa, the larval cuticula cracks along the 

 thorax as in an ordinary molt (beginning at the mid-dorsal line 

 of the metathorax and extending forward) and the pupa grad- 

 ually wriggles out by slowly contracting and relaxing the body 

 muscles. The larval skin passes off over the caudal end of the 

 body, where it may hang for several hours. At the beginning 

 of the molt, each leg, though fully formed, is curled up into i 

 little pad at the base of the larval leg, but as soon as they -are 

 free from the old cuticula they are straightened out so as to lie 



