THE AMERICAN ENTOMOLOGIST. 



i6i 



low, verging to reddish. It is a curious 

 fact that lapponica extends to the more 

 Southern States on this continent and is 

 sub-arctic in Europe ; while ircmulie, which 

 is sub-arctic here, extends to the more 

 southern countries of Europe. 



In meeting with the larvae of the two 

 commoner Western and Southern species 

 here mentioned {P. scripta and P. lapponica), 

 we have often endeavored to ascertain 

 whether they possess any differing charac- 

 ters that would permit us to decide posi- 

 tively which species of beetle they would 

 produce, and after a good many compari- 

 sons both of the living and preserved lar- 

 v», we have concluded that there are no 

 differences that can be positively relied on. 

 The latter species emits the milky fluid 

 more freely and has perhaps a more pun- 

 gent odor. The 



[Fig. M.l f ( D t , 



larva of P. tremulce 

 is at once distin- 

 guishable,however, 

 by its darker hue, 

 all the spots being 

 comparatively lar- 

 ger and broader, 

 and by having a 

 distinct spot on the 

 second and third 

 joints following the 

 head, in the dorsal 

 space which is so 

 pale and occupied 

 by mere specks in the other species. In 

 this respect tremula agrees with the Euro- 

 pean populi, which, being a larger species, 

 we here illustrate (Fig. 64), to show the 

 relative positions of the spots and tuber- 

 cles. This last larva is distinguished not 

 only by its larger size, but by the paler 

 prothoracic shield, which in all three of 

 the other species is dark. 



What with the injuries of the Cotton- 

 wood Borer {Saperda calcarata Say), which 

 are now most severe in the West, and 

 the defoliations by this leaf-beetle, the 

 Cottonwood, which has an especial value in 

 the West, both because of its rapid growth 

 and hardiness, seems doomed to follow the 

 Black Locust in succumbing to insect 



I,ARV\ OF Pl.AGIODERA POPULI: 



a, dorsal viewj b, side view of one 

 of middle joints ; c, ventral view 

 of same; (/, one of the tubercles — 

 greatly enlarged (after Riley). 



enemies. The Streaked Cottonwood 

 Beetle may, however, be managed by syr- 

 inging the trees with the wet preparation 

 of London Purple or other arsenical com- 

 pound. 



In order to illustrate the color variations 

 this Plagiodera scripta is subject to in the 

 perfect state, we tabulate below some of 

 the more marked varieties, with the re- 

 mark that various combinations of them 

 occur. 



VARIETIES OF PL.AGIODERA SCRIPTA. 



a. Typical. Black with a tinge of blue ; basal 

 joints of antennx beneath, thickened thoracic 

 margin with exception of a small round spot at 

 the middle, elytra with exception of suture and 

 three lines of interrupted black markings, base 

 of femora and part of tibise, and sides and apex 

 of abdomen, testaceous yellow. (Common 

 West). 



b. Variations in general coloration : 



/'. I. Base of antennae, head, underside, and 



legs, of the same yellowish color as upper 



side. (From Texas.) 



/>. a. Thorax testaceous-yellow, or more red- 

 dish, with the two lateral markings and a 

 2"-shaped mark on the disk blackish. 



6. . Thorax entirely testaceous-yellow. 

 6. 2. Principal color above and beneath blue ; 



legs blue. 



b. y. Sides of thorax as in typical form. Ely- 

 tra with faint yellow marking. (From 

 California.) 



b. S. Sides of thorax as in typical form. Ely- 

 tra unicolorous blue. (From California.) 



l>. e. Entirely blue, except a narrow lateral 

 yellowish marking each side on the last 

 abdominal joint. 



c. Variations in the markings of the elytra : 



c. I. Marked with black as follows : the suture; 

 two more or less oval spots near the base, 

 the inner of which is nearer to the suture 

 than to the lateral margin, and the outer on 

 the humerus ; three longitudinal strix on 

 the middle, the intermediate of which is the 

 longest ; subraarginal curved stria and an 

 oval spot between the latter and the suture. 

 (Common West.) 



c. 2. Additional marks ; A small triangular 

 basal spot in front and between the two sub- 

 basal markings. (Illinois.) 



c. a. This triangular spot is sometimes con- 

 nected with the humeral spot. (California.) 



c. p. Black markings become wider or longer 



and then often confluent. 

 c. y. Markings in general becoming smaller, 



either all of them , or one or several of them. 



