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A CASE OF EXCESSIVE PARASITISM.
By L. O. HOWARD.
June 17, 1896, the writer received from Dr. James Fletcher, of Ottawa, four little twigs of Arbor vitæ carrying specimens of the handsome Lecanium which Professor Cockerell has named L. fletcheri, in honor of the able Dominion entomologist. A few of the scales contained the exit holes of parasites, and the twigs were therefore placed in a small glass jar to save other parasites which might issue.
By June 27, ten days later, no less than 127 parasites had emerged. The scales were then counted and were found to be 80 in all. The holes in the scales were found to number 180, so that many parasites must have issued before they were received at Washington. Nor does the number of exit holes indicate definitely the whole number of parasites, since I have frequently known more than one parasite to issue from a single hole.
The results of the examination of the scales may be tabulated as follows:
Total number of specimens.
Of the 10 specimens in which no exit holes were found, 5 were discovered, upon dissection, to contain dead parasites; 3 were immature, and bad died from some undiscoverable cause; while with the remain. ing 2 the eggs had evidently developed and hatched. The total result is, then, a parasitism to the extent of 971 per cent.
Even up to this point the case is an interesting one, and affords an instance of extreme parasitism such as is seldom found. When the parasites were mounted up and studied, however, the exceptional—in fact unique-character of the occurrence became evident. No less than 6 distinct species of primary parasites of 5 distinct genera were found among them, and not a single hyperparasite. This would have been most remarkable liad it occurred in Southern California or the tropical toe of Florida, but coming from the cold climate of Ottawa it is little less than astonishing. When one reflects that there is hardly a species
of scale insect which is known throughout the whole of its geographical range (and many of them are now cosmopolitan) to have as many species of parasites as this, and that these all came from a single locality, nay, from a single hedge, and, in fact, from a single branch, how extraordinary it is! Further, they issued, not in different seasons, but all in practically the same week and from the offspring of probably a single mother Lecanium.
The list follows: 1. Coccophagus cognatus How.,
2 2. Coccophagus fletcher in. sp., 9
1 3. Aphycus pulvinariæ How., 9
4 4. Encyrtus flavus How., 8
4 Encyrtus flavus How.,
2 5. Chilonenrus albicornis How., 2 6. Blastothrix longipennis How.,
42 Blastothrix longipennis How.,
66 The writer's previous knowledge of these species has been about as follows:
No. 1. Hosts.—Lecanium hesperidum, Lec. cerasifex, Lec. persicæ.
No. 5. Hosts.-Lecanium sp., on pine; Lec. caryæ, Lec. sp., on Quercus aquatica; Kermes sp., 8 on oak.
Localities-District of Columbia; Davenport, Iowa; Bluffton, S. C.; Kirkwood, Mo.; England (?).
No. 6. Hosts.-Lecanium robiniarum, Lec. spp. undetermined.
I need only add that if collectors wish specimens of Lecanium fletcheri it will be well to apply to Dr. Fletcher at once, as it is reasonable to suppose that his Arbor vitæ hedge will be comparatively free from scales next season.
Coccophagus fletcheri n. sp. Female.—Length, 0.8 mm.; expanse, 1.65 mm.; antennal scape slerder, cylindrical, not reaching to middle ocellus; pedicel and first funicle joint subequal in length, the latter slightly wider; funicle joints 2 and 3 each slightly longer than 1, subequal in length, increasing very slightly in breadth; club long ovate, not flattened, nearly as long as whole funicle; entire flagellum with close, short, fine pile and sparse longitudinal carinæ; mesoscutum and axillae faintly shagreened; head and scutellum smooth; eyes hairy; bristles of head and mesonotum black; color moderately bright yellow; eyes and ocelli coral red; tip of scape and all of flagellum, border of pronotum, tip of tegulæ, border of metanotum, and incomplete bands between abdominal segments, fuscous; wings hyaline, veins fuscous.
One female, Coll. U. S. Nat. Mus., from Lecanium fletcheri, received from Ottawa, Canada, Dr. James Fletcher.
THE WALNUT SPANWORM.
(Boarmia plumigeraria Hulst.)
By D. W. COQUILLETT.
In former times it was quite generally believed that the walnut tree was singularly free from the attacks of leaf-eating insects. So pronounced was this belief that even economic entomologists of note recommended making a strong decoction of its leaves and spraying this upon other trees and plants for the purpose of protecting them from the attacks of leaf-eating insects. While this supposed immunity from insect attack may hold true in regard to our native species, this is not the case with the imported English walnut, as events in a certain locality in California have abundantly proven during the last few years. This tree is quite extensively grown in the southern part of the State, and in proportion to the care bestowed upon it from a cultural point of view yields a larger revenue than any other nut or fruit tree grown in that region.
During the early summer of the year 1890 there appeared in very large numbers a spanworm not heretofore known to be injurious, and attacked the leaves of English walnut trees in Santa Barbara County, Cal. Nearly every tree in a grove of 20 acres was attacked by them, but they were most numerous near the center of the grove, which would seem to indicate that they had been present in former years, but not in sufficient numbers to attract attention. The trees measured about 30 feet in height, and the branches expanded about 40 feet; and quite a large number of them had been almost defoliated by the span. worms. The owner of the grove had himself planted and cared for it, but had never previously observed any spanworms upon it, and, in view of the fact that the female moths are wingless, it is quite impossible to account for the sudden appearance of the worms in such unusual numbers.
The eggs from which these spanworms hatch are of a dark grayishdrab color, with a strong brassy tinge; they are flattened oval, as if compressed between the thumb and finger; the surface is quite rough, and bears numerous minute transverse ridges; at each end are many rather shallow punctures, and the egg measures about five-sixths of a millimeter in length. They are attached to the smaller twigs by one of their flattened sides in loose, irregular patches, and are not arranged in any given order. Sometimes as many as 200 eggs are deposited in a single patch or cluster.
The eggs are deposited from January to April, and hatch out in from ten days to two weeks from the time they are deposited. As soon as hatched the young worms begin to feed upon the tender leaves, and, when disturbed, let themselves down and hang suspended in the air by silken threads, after the manner of other spanworms. They are then of a blackish color, with a row of whitish spots along each side of the body and a pair of smaller whitish spots on each side of the first three sutures of the abdominal segments. They are furnished with only five pairs of legs. When about five days old they cast the skin for the first time, repeating the operation at the expiration of another five days, and twice again at intervals of about three days apart, there being four molts or castings of the skin before the worms transform to pupæ.
One of the full-grown worms is shown enlarged in the accompanying figure (40,a). The color is a light pinkish gray, varied with a darker gray or purplish, or sometimes with black and yellow, but never marked with distinct lines; the piliferous spots are black or dark brown, and the spiracles are orange yellow, ringed with black and usually situated on a yellow spot. The worms become full-grown in the latter part of April or during the month of May; they then enter the earth
5 to a depth of from 2 to 4 inches and form small cells, but do not spin Cocoons. The change to the chry.
FIG. 40.-Boarmia plumigeraria: a, larva-twice salis takes place shortly after the natural size; b, fifth and sixth segments, lateral cells are completed, and the chrys
view; c, seventh segment, from above-more en
larged (original). alids remain unchanged throughout the entire summer and until early in the following year, when they are changed into moths, which emerge from the ground from the first week in January to the last week in March. The male moth is winged, but the female is wingless and is so very different in appearance from the male that no one not familiar with the facts in the case would ever suspect that both belong to the same species. Both sexes are represented in the accompanying illustration (fig. 41), where a represents the male and b the female moth enlarged, the natural size being indicated by the slender lines. The species was originally described from a male speci. men. The discovery that the female is wingless will necessitate remov. ing it from the genus Boarmia and locating it near Phigalia.
This insect has thus far been found only in California and Oregon. Besides attacking the leaves of the English walnut, the writer has found these spanworms feeding upon the leaves of the apple, prune, and oak (Quercus agrifolia). There is a strong probability that this insect is a native of the Pacific Coast, where it originally fed upon the
leaves of the oak above mentioned, and that it has only within recent years acquired a taste for the leaves of cultivated trees.
At least one species of Tachina fly and a small four-winged ichneumon fly belonging to the genus Apanteles prey upon these spanworms; the small, white, silken cocoon of the last-named parasite may occasionally be found attached to the trunk of an infested tree, and near it the shrunken body of the spanworm in which the larva of the parasite had lived. Quite a large number of the spanworms are also destroyed by birds, notably by the different kinds of blackbirds, which appear to be particularly fond of them.
FIG. 41.—Boarmia plumigeraria : a, male moth; 6, female—twice natural size (original). Repeated experiments demonstrated the fact that the most efficient remedy for the destruction of these spanworms consists in spraying the infested trees with Paris green and water, at the rate of 1 pound of the poison to 200 gallons of water. This strength was found to be fatal to the worms, while the foliage was not injured by it. About 10 or 12 pounds of soap should be dissolved in each 100 gallons of this solution, in order to cause it to spread freely over the foliage. Almost any kind of soap, either soft or hard, will answer this purpose. Care should be exercised that the trees be sprayed when the worms are first hatched out. At this time a very little of the poison will prove fatal to them, whereas the nearly full-grown worms will consume a large number of the poisoned leaves before succumbing to the effects of the poison.