= > ~ | i. SB 818 C37 ENT 8 No. 105. Issued October 5, 1908. aited States Department of Agriculture, BUREAU OF ENTOMOLOGY, L. O. HOWARD, Entomologist and Chief of Bureau. THE ROSE SLUGS. By EF. H. CHITTENDEN, In Charge of Truck Crop and Special Insect Investigations. Roses grown in gardens in the United States are attacked by three species of sawfiies which live, in their larval stages, on the foliage, skeletonizing the leaves or cutting out holes of variable size and greatly disfiguring the plants. The larve, popularly known as “ rose slugs,” “ slugworms,” and “ roseworms,” have been classified as the American rose slug, the bristly roseworm, and the coiled or curled roseworm, respectively. For the sake of uniformity they may all be called rose slugs. The first of these, as its common name indicates, is native to America; the other two are evidently accidental intro- ductions from Europe, as they are now common to both hemispheres. As with most other sawflies,¢ they are found more abundantly in the North, but are quite troublesome as far southward as Maryland and Kansas. They practically confine their depredations to the flower garden, and roses are the only plants that are seriously damaged by them. Injury is due entirely to the larve, and the three species, each representing a distinct genus, differ considerably in appearance in all stages, as also in their life history and manner of work. | THE AMERICAN ROSE SLUG. (Endelomyia rose Harr.)? The American rose slug was first identified as a pest about the year 1831, when it did damage in gardens at Cambridge, Mass. At that time the species was somewhat restricted to that locality, but later, according to Harris, who observed and studied its habits,’ it grad- ually spread in that vicinity and by 1840 it had become so great a nuisance that a premium of $100 was offered for the most successful method of destroying it. “ Hymenopterous insects of the family Tenthredinide. 6 Synonyms: MWonostegia rose and Selandria rose. ¢ Report Ins. of Mass. Inj. to Veget., 1841, pp. 380-382; Flint ed., pp. 525-528. §4115—Cir. 105—O8 4 The female in depositing her eggs turns a little to one side, unsheaths her delicate saw-like ovipositor, and thrusts it between the two cuticles of a leaf, depositing a single egg in each incision. An egg is shown about natural size at d, figure 1, and much enlarged at e. The egg is of circular outline, much flattened, and measures about one-twentieth of an inch in diameter. Hatching begins in from ten days to two weeks after the eggs are deposited. The larve or slugs are to be found at work as early as the 1st of May in the District of Columbia, but their appearance in numbers is seldom noticed until the second or third week of that month. Obser- vations conducted at Washington, D. C., show that the periods men- tioned are subject to considerable variation. In 1905 the first sawflies of the new generation appeared June 2. Owing to the irregularity of appearance of the parent “ flies,” larve of the first generation may be found at work for a period of five or six weeks. Feeding takes place chiefly at night, and always on the upper surface of the leaves, the lower surface, ribs, and midribs remaining as a skeleton (fig. 1, ¢). The leaves are practically always skeletonized, not eaten into as in the case of the other two rose slugs, except when the larve are nearly grown. During the daytime the larva usually rests concealed on the under surface of a leaf (fig. 2, a). Sometimes the larvee are so abundant that not a leaf on a bush is spared, and the foliage looks as though it had been scorched by fire, and eventually drops off. The larvee are stated to be between two and three weeks in attaining their growth. They cast their skins several times, leaving them fastened to the leaves. After the last molting they lose their greenish hue and become opaque yellowish. They then descend into the earth to a depth of an inch or more, and each constructs for final transformation a somewhat fragile oval cell or cocoon coated with particles of earth. Here the insect remains as larva until the following spring, when it transforms to pupa shortly before issuance in May. The species is single-brooded, in which respect 1t resembles many other species of sawflies. REMEDIES. This rose slug and the others which will be discussed are quite easily controlled by several different methods. Sprinkling with water.—A strong stream of water directed upon the plants from different sides by an ordinary garden hose or large “Tt is evident from Harris’s account (1. ¢.) that in ascribing two generations to this rose slug he must also have had the bristly rose slug under observation. Miss M. E. Murtfeldt writes on this head that she has disproved Harris’s state- ment “by repeated rearing of the insect under close observation.” (41st Annual Rept. State Hort. Soc. Missouri, 1898, p, 288.) [Cir. 105] 5) syringe, if applied every day or two, will soon rid rosebushes of the pest. This is at the same time an excellent remedy for rose aphides or plant-lice. The insects are dislodged, fall to the ground, and are unable to return to reinfest the bushes. This remedy was tested practically by Dr. L. O. Howard many years ago. Paris green.—Where it is possible to apply them without danger of poisoning human beings or disfiguring the plants for ornament, different poisonous preparations are useful. Of these, Paris green, either dry or in solution, arsenate of lead, and white hellebore are good remedies. Paris green is best used as a spray in the proportion of an ounce to a gallon of water. Applied dry, it is mixed with 20 parts of flour or similar diluent and puffed on the plants by means of a powder bellows or insufflator. For use in large gardens, however, the poison is employed at the rate of 1 pound to from 75 to 125 gallons of water, lime being added in about the same proportion as Paris green to prevent scorching. For properly mixing and applying this insecticide a sprayer of good quality should be used. Sprinkling with a watering pot or with a whisk broom will not answer the pur- pose and is, moreover, dangerous to tender foliage. The Paris green is first mixed with a small quantity of water into a fine paste before the bulk of water is added and should be churned in the sprayer or force pump until thoroughly blended. The resulting mixture, being a mechanical one, is not constant and the arsenical sinks to the bot- tom. The solution should therefore be constantly stirred while being applied in order that an even application may be made. In applying an arsenical spray an effort should be made to reach all of the leaves, which may be accomplished by spraying from two sides. Two or three applications will suffice for the spring generation of rose slugs. Scheele’s green and some other arsenicals can be used instead of Paris green. Arsenate of lead.—< still more valuable insecticide for such insects as rose slugs and other leaf feeders is arsenate of lead, but its use is open to the objection that it discolors the leafage, leaving a white deposit, which is not, however, permanent. It is applied in practi- cally the same manner as Paris green and is a less poisonous arsenical, and, being sold in paste form, is used at a considerably greater strength—about 1 pound combined with 15 to 25 gallons of water or Bordeaux mixture. Being adhesive, it adheres more firmly to the leafage and is much less likely to produce scorching." Hellebore.—Hellebore is used at the rate of 1 ounce to from 2 to 3 gallons of water, and kills by contact as well as by its poisonous effects @ Additional information in regard to the preparation and use of arsenate of lead and other insecticides is given in Farmers’ Bulletin 127, which may be had gratis on application to the U. S. Department of Agriculture. [Cir. 105] 6 when eaten by the insect. It is less poisonous to man than an arsen- ical, but not so effective to leaf-feeding larve. It may also be applied dry mixed with about double its weight, or more, of powdered plaster or cheap flour. When not in use the receptacles containing poisons should be plainly labeled “ Poison!” and placed on a high shelf or in a locker out of the reach of children. Properly applied, there is no danger, in using an arsenical on ornamental plants, of poisoning human beings, or domestic animals other than rabbits or similar pets. Soaps and other washes.—Oily soaps, such as fish-oil or whale-oil soap, and other soaps, and tobacco water will kill these insects, but their use is open to the objection that if apphed just before or at blossoming they are apt to injure the petals of delicate flowers, and whale-oil and tobacco also leave an unpleasant odor.