THE BIOLOGY OF THE ALDER FLEA-BEETLE. 263 



Coloration after the first molt (second instar). 



The coloration of the larva after the first molt does not differ from 

 the coloration after the second molt, and is described in detail under 

 the latter heading. 



Color description of a second instar larva, early. 



Head, prothoracic and anal shields, and legs, shining black; general 

 body color brownish black dorsally, lighter ventrally; dorsal and lateral 

 tubercles dull black; ventral tubercles but little darker than the body. 



Color description of a second instar larva, late. 



Head, prothoracic and anal shields, and legs shining black; general 

 body color very dark golden brown dorsally, somewhat lighter ventrally; 

 dorsal and lateral tubercles dark brown; ventral tubercles same color 

 as the rest of the underparts. 



The molt to the third instar (second molt). As is the case 

 with arthropods in general, when the larva is ready to molt, a 

 new cuticula is formed underneath the old one, and late in each 

 instar, the old cuticula becomes very brittle. In the process of 

 molting, it cracks first along the mid-dorsal line of the meta- 

 thorax, the slit extending cephalad along the mid-dorsal line of 

 the other thoracic segments, and the V-shaped epicranial suture 

 of the head. During this time the larva is firmly attached to 

 the leaf by the legs of the skin which is being shed, the tarsal 

 claws of which are securely imbedded in the tissues, and by 

 the anal proleg, which projects out a little beyond the old cuti- 

 cula. By slowly and regularly contracting and relaxing the 

 body muscles, the larva works its way out of the old skin; first 

 the thorax is arched out and then the head is freed. The 

 legs are drawn out almost immediately after the head, but as 

 they are soft and weak, they are held closely appressed to the 

 body, and the larva makes no attempt to walk for about half 

 an hour. The insect is now attached to the leaf only by the anal 

 proleg, and the old cuticula is left as a ring around 3 or 4 of the 

 abdominal segments. This ring is finally pushed off over the 

 anal proleg, mainly by the activities of the body muscles, 

 although the legs are used a little at the end. 



This molt was observed several times; a typical example is given 

 below: 11.05 skin cracked along the metathorax; 11.15 head free; 11.17 

 legs free; 11.25 old cuticula left like a ring around the abdomen, which 

 is about two-thirds free; 11.40 begins to walk; 12.05 entirely out of the 

 old cuticula. 



Coloration after the second molt (third instar): At the 

 beginning of the molt, the larva, as it emerges from the old skin, 

 is a pure orange yellow, except that the mandibles are reddish 



