1879.1 



AND HORTICULTURIST. 



339 



THE ROSE SLUG, (SELANDRIA ROS>E, 

 HARRIS). 



BY MISS MARY C. MURTFELDT, KIRKWOOD, MO. 



The rose is undoubtedly beset by a greater 

 variety of insect enemies than any other garden 

 shrub. Among these pests the well known and 

 wide-spread " slug " has a " bad eminence." 

 This insect was first^ described and named by 

 Dr. Harris, in his Insects Injurious to Vegetation, 

 in which account the statements concerning it 

 are mainly correct, but the Doctor omits certain 

 interesting particulars in its history and makes 

 one serious mistake. 



With us, in the latitude of central Missouri, 

 the parent flies appear as early as the first of 

 May, when they may be observed in consider- 

 able numbers on the rose bushes, where their 

 sluggish habits admit of their easy capture. 

 They are about one-fifth of an inch in length, of 

 a glossy black color, and have the wings closely 

 folded when at rest. The females soon begin 

 the process of oviposition. With their saw-like 

 ovipositors they pierce the edges of the leaves 

 and force their eggs toward the tips of the' 

 serrations under the cuticle on the under side. 

 The egg is circular, about one-twentieth of an 

 inch in diameter, and so flat at first as to be im- 

 perceptible except upon the closest scrutiny. 

 It hatches in eight or nine days, and before the 

 larva escapes, swells considerably, appearing 

 like a minute blister on the under side of the 

 leaf, within which the coiled embryo is dis- 

 tinctly visible. The young slug upon emerging 

 is one-tenth of an inch in length, and about the 

 diameter of No. 30 spool cotton, the round, 

 tawny-yellow head being the broadest part. The 

 color is greenish white with a dark-green vesicu- 

 lar line as soon as it begins to feed. When full 

 grown it is rather more than one-third of an 

 inch long, broadest at the thoracic joints, the 

 color being a translucent dull yellow, shading to 

 green on the back. It is not in the least slimy, 

 as are some closely allied species, but on tlie 

 contrary has a velvety surface. It feeds at night 

 upon the green tissue of the upper surface of the 

 leaf, and rests during the day hidden upon the 

 under side. It attains its growth in fourteen or 

 fifteen days, molting meanwhile four times. 

 After the last molt it ceases to feed, acquires a 

 more opaque color, and soon drops or crawls to 

 the ground into which it burrows to the depth of 

 an inch or two, and encloses itself in a frail, 

 oval cell formed from particles of earth ce- 

 mented with a viscid excretion. "The slugs 



having finished their transformations," Harris 

 proceeds to say, " and changed to flies within 

 their cells, they come out of the ground early 

 in August, and laj' their eggs for a second brood 

 of young. These in turn perform their ap- 

 pointed work of destruction in the Autumn; 

 they then go into the ground, make their earthen 

 cells, remain therein throughout the Winter, 

 and appear in the winged form in the following 

 Spring and Summer." 



This is the point where Dr. Harris is in error, 

 unless the rose slug of Massachusetts is a difter- 

 ent species from the one from which we suffer, » 

 which, as the two insects seem to agree in all 

 other particulars is scarcely supposable. Hav- 

 ing watched the insect through its transforma- 

 tions for several successive j'ears, I am con- 

 vinced that it is not double-brooded with us, and 

 as our season is much lonucer than Summer in 

 Massachusetts, it stands to reason that it is not 

 double-brooded in more northern latitudes. 

 Dr. Harris, in making this statement probably 

 reasoned from analogy, as the cherry slug and 

 several other closely allied species are doul)le- 

 brooded; but it is not always safe to reason thus 

 in the case of insects, as there is often great di- 

 versity of habit among species nearly related. 

 As Dr. Harris's mistake has been followed by 

 all the subsequent writers on the subject, it oc- 

 curred to me that it would only be the part of 

 kindness to rose culturists to undeceive tiiem, or 

 rather to reassure them on tliis point. There is 

 an adage to the effect that " it is not necessary 

 to paint a certain personage blacker than he is," 

 which holds good in the present case. It is cer- 

 tainly bad enough to have to contend with one 

 bi'ood of this destructive pest, without the dis- 

 couraging information that almost as soon as 

 the Spring brood disappears the Autumn brood 

 will hatch. Therefore, let all who enfOrtain 

 such fears take heart. If the slugs can be kept 

 from blighting the foliage dnrhig the months of 

 May and June, no further trouble need be ap- 

 prehended from them until the following year, 

 as they remain unchanged within their cells for 

 more than ten months. Although the individual 

 larva feeds only for about two weeks, yet as the 

 flies live and continue to lay their eggs for some 

 time, the sluijj season lasts for nearly a month, 

 and if the insects are neglected at the end of 

 that time the foliage of the infested plants, with 

 the green tissue eaten in large irregular patches 

 from the upper surface, will appear as though 

 scorched with fire. Bourbon, Tea, and other 



