THE MAGNOLIA SCALE (NEOLECANIUM CORNUPARVUM THRO.).

Transcription

1 THE MAGNOLIA SCALE (NEOLECANIUM CORNUPARVUM THRO.). GLENN W: HERRICK, Cornell University. It is always of great interest to watch the" ups and downs" of insects-to observe the enormous abundance of a certain species over a period of years and then note the gradual subsidence of the speciesthrough the followingyears. For instance, it has actually been difficult during the last few years to find enough fresh specimens of the San Jose Scale about Ithaca for study in the laboratory and for observance in the field. On the other hand the magnolia scale (N. cornuparvum) has apparently been increasing in numbers during recent years. My attention has been called, by correspondents, to excessive infestations of the scale followed by serious injury to its host plants, Magnolia liliflora and Magnolia soulangeana. The scale has been especially prominent in the city of Ithaca and its outlying districts. Undoubtedly the magnolia shrub is becoming more popular as an ornamental and is therefore more commonly planted. Th~s the scale has found its host plentiful and readily accessible. Again, the natural enemies of the scale may have been scarce during the last few years in which event the insect has probably had little to retard its abnormal increase. I have not seen any evidence of parasites working on this coccid and have not been fortunate enough to rear any parasitic forms from the scale. HISTORY AND DESCRIPTION. This magnolia scale existed undescribed until It had been known previous to that time but had been looked upon and discussed as the species, Lecanium magnoliarum. In 1no;) it was recognized as a distinct species and described by Thro. as Lecanium cornuparvum but was later placed in the genus Neolecanium (Fernald 1903 and Sanders 1909). The female scales, the only ones known to exist, for the males have not been observed, are among the largest and most conspicuous of our scale insects, (PI. I, Fig. 4). 302

2 1!l:n] lierrick: lvfagnolia Scale 303 The f{'males, when grown, become about 72 of an inch in length (N-lO mm.). The body is notably convex and is covered with an abundance of white waxy bloom. When numerous, the host plant looks as though it were covered with masses of white cottony material. When the waxy bloom is removed the body of the scale appears shining brown with numerous honey-comb-like pits and large glands. On removal of the body from the branch, an elliptical scar is left on the bark with four distinct, white lines converging toward the center. These lines mark the position of the spiracular grooves of the insect. The legs are short and stubby and the antennre have but six, short, indistinct segments. The overwintering nymphs (PI. I., Fig. 3) are nearly black with a bluish waxy bloom. They are elliptical in outline and somewhat narrower behind. The median carina is high and prominent and slightly lighter in color than the remainder of the body. From 8 to 9 transverse carinre are present on each side of the median ridge. On each edge of the body are two white spots indicating the entrance to the spiracular grooves. The nymphs vary from.96 to 1.01 mm. in length and from.62 to.i(i mm. in width. The first instar nymph has long, five-segmented antennre and long slender legs ending in a distinct claw (PI. I, Fig. 1). The second instar nymph has short, stubby antennre and legs CPl. I, Fig. 2). seta~. There are three short, stout, spiracular FOOD PLANTS AND DISTRIBUTION. Thro made his original description of the species from specimens taken from Magnolia at Trumansburg, New York. Sanders says it occurs on various species of magnolia including the deciduous Af. acuminata of the Northern States. Dietz and Morrison (HHG) collected it once in Indiana. Houser (1HIN) records the scale from several places in Ohio on Magnolia and says it has been reported from Daphne and Virginia Creeper, but t h('se t "'0 records in all probability refer to L. magnoliarum.,ye have it here in Ithaca on M. liliflora and M. soulangeana. Pettit and l\icdaniel (Hl20) record it from the cucumber-tree at Orwell, Ohio. Dr. Harold Morrison of the U. S. Bur. Ent. very kindly gave me a list of the States from which the scale has been eollected according to the records of the Bureau which TUn as follows:

3 304 Annals Entomological Society of America [Vol. XXIV, STATE No. OF RECORDS Alabama Connecticut ' Florida Georgia Indiana Kentucky Louisiana,, Maryland, STATE LIFE HISTORY No. OF RECORDS Mississippi, " New york,., Ohio P~~s~lvania 33 VlrglnJa, 1 South Carolina West Virginia The insect hibernates as small first stage nymphs on the newer wood. The number of overwintering nymphs is often very great and every available space on the bark is taken up. The nymphs molt rather early in the spring-during the second week in May in In the first half of June they molt again when each one assumes the elliptical, thickened convex form of the adult. At this time the nymph is of a dark slate, almost purplish color and from 2%:to 2% mm. in length. In about a week each nymph excretes the white layer of wax over the body and each one soon looks like a small snow-white lump of dough clinging to the bark. The nymphs grow slowly during July but by early August a few females may be found which are mature and have brought forth their first young. For instance, on August 2, during the season of 1929, out of several females examined one had 12 nymphs beneath the body (the females are viviparous). This female had matured early for the other four examined were not yet full grown and had no young. By the latter part of August the majority of the females had matured and had brought forth their young, many of which had already settled on the branches. Some, however, on this late date had only begun to bear young which were still beneath the body of the mother scale. There is thus but one generation a year here at Ithaca. LITERATURE CITED. Thro, Wm. C. Distinctive characteristics of the species of the genus Lecanium. Cornell University Agr. Expt. Sta. Bull. 209, p. 216, Fernald, M. E. Catalogue of the Coccidae. Mass. Agr. Expt. Sta. Sprc. Bull. 88, p. 176, Sanders, J. C. The identity and synonymy of some of our soft scale insects. In Jour. Ec. Ent., Vol. 2, p. 448, Dietz, Harry F. and Morrison, Harold. In the Coccidae or Scale Insects of Indiana, p. 247, Houser, J. E. The Magnolia Scale. In Bull. 332, Ohio Agri. Expt. Sta., p. 302, Pettit, R. H. and McDaniel, Eugenia. In the Lecania of Michigan. Mich. Agri. Expt. Sta., Tech. Bull. 48, Wilson, C. E. In Scale Insects of Florida. The Quarterly Bulletin of the State Plant Board of Florida, Vol. VII, No.4 (July), p. 265, 1923.

4 Mag-nolia Seale GIl'nn \Y. Herrick PLATE 1. FIG. 1 Fir~t stag-e of mag-nolia scale. FIG. 2 Second stag-e of magnolia scale. l)yerwinh'ring FIG. 3 nymphs of the magnolia scale. FIG. 4 Adults of the magnolia scale. (Natural size:) 305

5