REPORT OF THE ENTOMOLOGIST. 



305 



months of May and June, it is difficult to iiud a plant that is not blotched 

 and discolored by the larvae of this flea-beetle, many plants being en- 

 tirely killed thereby. The larva is not confined to a single mine or even 

 to a single leaf, bat will leave one mine and form another in some cases 

 where there is no evident reason for so doing. When full-grown (Plate 

 IV, Fig. 1, a) it crawls or drops to the ground and pupates in an oval cell 

 just beneath the surface (Plate IV, Fig. 1, c, pupa). The eggs are depos- 

 ited upon the upper surface of the leaf along the mid-vein, and are each 

 about 0.02™ ra long, or just large enough to be perceptible to the un- 

 aided eye. They are of a depressed, oblong shape, glued singly and 

 flatly to the leaf. The color is dull white, with a tinge of green, and 

 the surface under the lens appears fretted or shagreened. 



The young larvae work their way from the under side through the 

 cuticle of the leaf. In May and June the entire cycle of development 

 from egg to perfect insect occupies only from twenty to twenty-two or 

 twenty- three days. The only other plant except the Lepidium which 

 the larvae have been found to mine is the delicate and pungent Arabis 

 ludoviciana, which is sparingly attacked. 



The male of this species is readily distinguished from vittata by the 

 dilated fifth joint of the antenna3 (Plate IV, Fig. but the females 

 are less easily separated, and in order to bring out more strikingly the 

 differences which invariably distinguish these two beetles, which in gen- 

 eral appearance are so easily confounded, we have drawn up, from abund- 

 ant material of both species, the following comparative table: 



Zimtnermanni. 



Ovate, convex. 



Vittata. 



FORM. 



| Oval, more convex. 



HEAD. 



Strongly carinato anteriorly, front 

 6niooth, shining with line median sulcus; 

 vertex finely and transversely aciculate 

 and sparsely and finely punctulate. 



Strongly carinate anteriorly, front 

 smooth, shining, with distinct median sul- 

 cus ; vertex not aciculate, sparsely, but 

 more clearly punctulate. 



ANTENN7E. 



Differing considerably in length and 

 structure according to the sexes. Joints 

 2, 3, 4 reddish : joint 1 blackish above and 

 reddish beneath. 



Not differing much in length and struct- 

 ure according to the sexes. Joints 1,2,3 

 clear reddish yellow. 



THORAX. 



Usually finely and transversely acicu- 

 late, moderately and sparsely punctulate, 

 pu notations larger at base and sides than 

 m front. 



Aciculation usually not obvious, punc- 

 tation variable but usually denser. 



ELYTRA. 



Almost parallel at the sides. Sculpture 

 variable in strength, punctations ar- 

 ranged in rows on the disk. 



Yellow vitta not much subject to varia- 

 tion, hardly over interrupted at middle, 

 usually pale and narrow, incurved only at 

 apex; deeply and widely eraarginate at 

 outer side, inner side almost straight. 



20 A — '84 



Roundedat the sides. Sculpture variable, 

 but usually finer and less distinctly ser- 

 iate. 



Yellow vitta considerably subject to va- 

 riation, frequently interrupted at middle, 

 usually bright yellow and wider; incurved 

 at base and apex; very deeply emarginate 

 at outer side, inner side sinuate. 



