i6o 



THE AMERICAN ENTOMOLOGIST. 



gree, even where growing in the neighborhood of 

 the injured Cottonwood. This is partlj^due, per- 

 haps, to the fact that the Willow does not suffer 

 so much from defoliation as does the Cottonwood, 

 though it is possible that a special Coltonwood- 

 feeding race of the species has been of late years 

 developed in those sections where the tree is so 

 largely planted. This would be parallel to the 

 well-known case of the Apple-maggot (T'n^c/a 

 pomonella), which, though infesting wild haws and 

 crabs in all parts of the country, has only taken 

 to feeding on and injuring cultivated apples in 

 some of the New England States. The Cotton- 

 wood could probably be freed from the injuries of 

 the beetle we are considering by syringing the 

 trees with Paris-green water. 



The perfect beetles, as is generally the 

 case with the members of this family, hiber- 

 nate in sheltered situations. They may be 

 seen pairing and laying soon after the Cot- 

 tonwoods begin to leaf in the spring. The 

 eggs (Fig. 6 1, a)^ which are elongate-oval, 

 of a pale yellowish-white color, rather soft, 

 and about o.s"""- long, are laid in dense 

 clusters of ten upward to a hundred. 

 When first hatched the larvae are almost 

 wholly black, and congregate near their 

 egg shells, skeletonizing the leaf as shown 

 in Fig. 6i, r. In the month of June we 

 found the second brood of larvae in Ne- 

 braska just hatching and commencing to 

 work, and we had the assurance of Prof. 

 Aughey that there were at least three annual 

 broods. We think it probable that there 

 are even more, as the insect is not only a 

 voracious feeder, but goes through its trans- 

 formation with great rapidity, only fifteen 

 days being required in the month of August 

 from the hatching point to the issuing of 

 the perfect beetle, as has been determined 

 by Prof. F. H. Snow.* We found the in- 

 sect in all stages everywhere in Colorado 

 where the Narrow-leaved Cottonwood was 

 growing. The larva is marked, as shown 

 in Fig. 6i, ^'j and Fig. 64, a, and we ap- 

 pend a more detailed description of it 

 when full grown : 



Plagiodera scripta — Larva — color dingy, yel- 

 lowish-white ; head and legs polished black. 

 Venter with three rows of dusky, highly polished 

 spots becoming confluent on joints 11 and 12, 

 the middle row double but confluent. On joints 

 2, 3, and 4, the outer rows are represented by a 

 mere speck, and on joint i they are obsolete. 

 Laterally there are two rows of somewhat darker, 

 more elevated tubercles, the upper row the 



* Observer 0/ Nature, Lawrence, Kan., November 23, 1875. 



largest, the lower one obsolete on thoracic joints. 

 Dorsally there are four distinct rows, the outer 

 rows consisting of distinct tubercles from the 

 tops of which a milky fluid can be thrust. On 

 joints 2 and 3 these tubercles are somewhat 

 lower down than on the other joints, and 

 raised on a bulbous swelling, and the interme- 

 diate space between them and the medio-dorsal 

 tubercles is swollen and paler than the rest of 

 the body, and surmounted by two or three quite 

 minute dusky specks. The stigmata are black, 

 the first pair on a fold which seems to be- 

 long more to the second than to the first joint, the 

 others normally placed between the upper 

 lateral and lower dorsal tubercle. Pseudo-pod, 

 pale. 



There is a closely allied species, the 

 Plagiodera lappotiica Linn. (Fig. 63), which 



[Fig. 62 



Plagiodera scripta : 

 showing variations (after Riley). 



feeds more particularly on Willow, as we 

 have found it quite commonly on Black 

 Willow in Missouri. The accompanying 

 figure will show the more perceptible color- 

 ational differences between this and the 

 preceding species, the more constant struc- 

 tural difference between the two consisting 

 in the claw-joint being dentate 

 beneath in scripta, and simple 

 in lapponica* But the larvae 

 of the two are so much alike as 

 not to be easily distinguished 

 even upon the closest scrutiny. 

 A third species of the genus, 

 viz., P. tremulcB Fabr., is found 

 in the more northern parts of the conti- 

 nent, and like P. lapponica, it is common to 

 both Europe and America. Here it injures 

 the leaves of the common Aspen {Populus 

 tremuloides), the beetle itself being easily 

 distinguished by the uniformly steel-blue 

 color, with the exception of the wing-cov- 

 ers, which are just as uniformly clay-yel- 



* As both species are very variable and both have the uni- 

 formly steel-blue form, and as their larvse are undistinguish- 

 able, it may be questioned whether this structural feature can 

 be relied on, and we opine that lapponica (Linn.) like conflu 

 ens (Rogers) and perhaps obsoleta (Say) are but pronounced 

 forms of this scripta^ though science will be best served by 

 referring to them under their several names. 



Plagiodera 

 lapponica. 



