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CIRCULAR No. 38, SECOND REVISE. Issued September 3, 1908.
United States Department of Agriculture,
BUREAU OF ENTOMOLOGY. L. O. HOWARD, Entomologist and Chief of Bureau.
THE SQUASH-VINE BORER. (Melitta satyriniformis Hbn.)4
| By F. H. CuirrenpDen, WERE In Charge of Truck Crop and Special Insect Investigations.
GENERAL APPEARANCE AND METHOD OF WORK.
One of the most troublesome of the many enemies of squashes, pumpkins, and other cucurbits is the squash-vine borer. In many | localities this spe- | cles surpasses all other squash in- sects in point of injurioushess. |; Damage is due | to the larve bor- ing through the ystems, causing | them to rot at.the affected points and become sev-
ered from the ch ia se Fig. 1.—Squash-vine borer ( Melittia satyriniformis): a, Male moth; 6,
gene; or pO njur- female, with wings folded at rest; c, eggs shown on bit of squash stem;
ing the vine as to d, full-grown larva, in situ in vine; e, pupa; f, pupal cell. All one-third
larger than natural size (author’s illustration).
cause the leaves
to wilt and the plant to die. The presence of the borer feeding within | the stem is not apparent at the commencement of the attack, but soon | becomes manifest through the presence of the coarse yellowish excre- | ment which it forces from its burrow in the stem and which accumu- | lates on the ground beneath, as well as by the sudden wilting and dying | down of the leaves. Wilting occurs soon after the larve have made
| @ Inearly publications this species was generally known as Melittia ceto, or cucurbitex. |’ For reason of change of name see writer’s article in Bul. 19, n. s., Div. Ent., p. 38.
2
considerable growth within. From one to half a dozen or more larve inhabit a stem, and often upward of forty individuals have been taken from a single plant; indeed, one grower has stated that he once cut ‘142 larve from a single vine.” The larve work with great rapidity
and in a very short time are able to injure a plant so that no fruit
will mature. Injury is most noticeable near the base of the stems, where in course of time the vine becomes severed from the roots and the whole vine dies.
The parent of this insect is a beautiful creature, a medium-sized moth of the family Sesiide, or clear-winged moths. The fore wings are opaque, lustrous olive-brown in color, with metallic green reflections, and expand from less than an inch to nearly an inch and a half. The hind wings are transparent and veined as shown in the accompanying illustration of the male (fig. 1, a). The abdomen is conspicuously marked with orange or red, black, and bronze, and the hind legs are fringed with long hairs—red or orange on the outer _ surface and black inside. The natural position of the moth when at rest is shown by the figure of the female (0).
DISTRIBUTION.
As far as known, the squash-vine borer is a native of the Western Hemisphere, and widely distributed and injurious in the United States practically wherever squashes are cultivated. Available rec- ords and examination of material in the collection of the U.S. National Museum show that it has a range embracing territory from the New England States and Canada, in the north, to the Gulf States south- ward, and westward to the region beyond the Missouri River, which comprises the major portion of the Carolinian and Austroriparian areas of the Upper and Lower Austral life zones and a portion also of the Transition zone. Injury has been observed to be particularly severe in recent years on Long Island and in New Jersey, Delaware, Maryland, Virginia, and the District of Columbia, in the East, and in
Kansas and Nebraska in the West. Other States in which injury |
has been noted include Maine, Massachusetts, Connecticut, Rhode
Island, Georgia, Alabama, Mississippi, Louisiana, Iowa, and Michi- }
gan. It is evidently of tropical origin, and occurs in Mexico, where it is also widely distributed, and in Guatemala, Panama, Venezuela, Argentina, and the Lower Amazon.
FOOD HABITS.
The vines of squash and pumpkin form the chief food supply of |
this insect, but occasionally it attacks also the gourd, muskmelon, and
cucumber. It does not, however, in the writer’s experience, infest |
melons and cucumbers when the other preferred crops are available.
The larve bore through the stems from the roots to the base of and
[Cir. 38]
~~
|
3
even through the leaf-stalks, and young larve may be found even in
_ the larger veins, into which they bore when the eggs have been placed
in such locations, and often attack the fruit. They also penetrate
_ gourds so hard that it is difficult to cut into them with a sharp knife.
Laer have been observed on the wild balsam apple (Lehinocystis
_ lobata), which is probably a natural food plant.
Injury is greatest to Hubbard, marrow cymlings, and other late
_ varieties of squash, and is apt to be more acutely felt in small gardens
than where crops are grown for market. Even if the plant survives attack it may not bear fruit, and often the grower loses a large propor- tion of his crop year after year. Not infrequently entire crops are
destroyed.
NATURAL HISTORY.
This species is injurious only in the larval form. Although the larve are familiar objects to squash growers, the moths are not gener- ally recognized as the parents of these pernicious borers.
The moths, unlike most others, fly only during the daytime and in the heat of the day. Toward twilght they become less active and may be seen sitting quietly on the leaves of their host plants. Both when in flight and when at rest the moths are singularly wasp-like in appearance. :
Time of appearance of the moth—Approximately it may be stated that the moth appears as soon as the vines are sufficiently advanced to serve for oviposition and the subsequent subsistence of the borer larvze within their stems. Indications are that as far south as the District of Columbia the moths make their first appearance in the field some time ~ in May, or at least early in June, as larve nearly matured have been found by the middle of July. In New Jersey, according to Dr. J. B. Smith, the moths are abroad at or soon after the beginning of June; on Long Island, from the middle tothe last of June. In Massachusetts, : according to Harris, they appear about the plants the second week in July. We thus have considerable variation in time of earliest appear- ance, dependent upon season and locality—a variation to be expected in a species of so wide a range.
The egg and oviposition—The eggs, which are oval and dull red in color, are laid upon all parts of a plant, from the roots to the buds and petioles, but chiefly along the stems, although in some varieties of squash, it is said, nearer the base of the stem than otherwise. Ovi- position is very rapid, the moth flitting from hill to hill, leaving an egg ineach. Asingle moth may lay as many as 212 eggs. The eggs hatch in from six to fifteen days after they are deposited, and the larve are said to attain full growth four or more weeks later. This period will
_undoubtedly vary in different temperatures, according to the season of
the year when oviposition takes place. [Cir 38]
-
Eggs are shown a little larger than natural at c of figure 1, and much magnified at a and 6 of figure 2, c showing the sculpture.
The ‘arva.—The larvais a soft, whitish, grub-like caterpillar of nearly cylindrical form, with a small, dark head and a few very sparse hairs on each segment. lLarve in the earlier stages of growth are illus- trated by d, e, and fof figure 2. A full-grown larva is shown in profile within an open stem at figure 1, d, and the head and first two thoracic segments appear in figure 2 at g. Mature larve measure about an inch (25 ™™ in length). In the District of Columbia full-grown larve, as already observed, occur as early as July 16; in New Jersey, later in July, and are to be found upon the vines in different stages in October; at Washington, as late as the second week of November.
After attaining maturity the larve desert the stems and enter the earth, burving themselves to the depth of 1 or 2 inches, and form their cocoons, in which they transform to pupe. The cocoon (fig. 1, f) iscon- structed of silk and coated externally with fine parti- cles of earth, which adhere on account of somegummy secretion of the larva.
The pupa or chrysalis (shown in profile at e, fig. 1) measures about 2 inch Fig. 2—Squash-vine borer (Melittia satyriniformis): a,F gz in length (16 mays iHans
as seen from above; b, same from the side, showing sculp- 1 siesta 2 | = 13 f ture; c, sculpture of egg, greatly enlarged; d, newly hatched Siping ma 1logany rown
larva; e, half-grown larva; f, head of same from side; 9 jncolorandits head isorna- head of mature larva from above; a, 6, and c, much en- : 5 larged; d, e, f, and g, less enlarged (author’s illustration) . mented in frontjust above and between the eyes with a horn-like process. By means of this the pupa cuts its way out of one end of its cocoon and by the aid of the abdominal hook-like spines forces itself to the surface of the earth before transforming to adult. Number of generations.—The question of the number of generations produced annually in localities of different temperatures which this insect inhabits has been solved by actual observation, the results sery- ing to indicate that it is practically single-brooded on Long Island and northward; that there is a tendency to two broods in New Jersey, thé moths in exceptional cases completing their transformations late in August or September; that in the latitude of the District of Columbia the species is partially double-brooded, a larger portion of the moths, we may assume, developing as a second generation here than in New Jersey; and that in the Gulf States this series is undoubtedly fully two-brooded.
[Cir. 38]
5
PREVENTIVE AND REMEDIAL MEASURES.
This borer is an exceptionally difficult insect to control, as ordinary insecticides are of no value after the insect has once entered the vines, and repellents are also practically useless. We are, therefore, depend- ent upon cultural methods for relief.
Knowing that the insect passes the winter in the fields which it has ravaged, it should be superfluous to caution growers against planting squashes in the same ground in successive years.
Early squashes as traps.—Good results have been obtained by plant- ing as a trap crop and as early as possible a few summer squashes, such as crooknecks and early cymlings, before and between rows of the main crop of late varieties. The summer squashes attract the insects in such numbers as to leave a smaller number to deal with upon the late or main crop. As soon as the early crop is gathered, or earlier if the ground is needed for the main crop, the vines are promptly raked up and burned to destroy all eggs and larve which they may harbor, and the same treatment is followed after gathering the late varieties. This method, according to Dr. J. B. Smith, has proved profitable where used in New Jersey, and should produce good results farther north. Southward, where two well-defined broods appear, it might not be so productive of good, but it should be given a thorough
test.
Fall harrowing and deep spring plowing—Experiments conducted by Mr. F. A. Sirrine, of the New York Agricultural Experiment Station at Geneva, N. Y., show that this species can be greatly reduced by lightly harrowing the surface of infested squash fields in the fall so as to bring the cocoons of the vine borer to the surface, where they will be exposed to the elements, and then plowing in the spring to a uni- form depth of at least 6 inches, so that the adults will not be able to issue.
Other cultural methods.—When the vines have attained some length parts of them should be covered over with earth, so that secondary roots will be sent out to support the plants in case the main root is injured by the borer. Keeping the plants in good condition, free from other insects and from disease, and well nourished with the assistance of manure or other fertilizer if necessary, will also aid the plants to with- stand borer attack. When vines are so badly infested as to be incapa- ble of bearing fruit they usually die at once, and they should then be promptly taken out and burned. The old vines should also be- destroyed as soon as the crop is made.
Cutting out the borers.—The old-time remedy of cutting the borers out of the vines, although laborious, is useful, and about the only method open for employment after they have entered the vines. As
several individuals often infest a single vine, it is best to cut longitudi- (Cir. 38]
6
nally, so as not to sever the vine from the root stalk. If the wound made by cutting be afterwards covered with moist soil it will assist it to heal. The location of the borer in the vine can be readily detected by the accumulation of its yellow ‘‘frass’’ or excrement at the point where it is working, and which is kept open for the extrusion of this matter.
Capturing the moths.—This species may be held in partial subjection by keeping a sharp lookout for the parent moths, which are readily seen and not difficult of capture toward dusk or in the cool of the morning, when they are comparatively inactive. The female may then be easily caught, just as she alights on a vine for oviposition.? Several persons, including the writer, can vouch for this statement. _ Summary.—lIf the grower would make certain of securing a good crop in localities where this and other enemies of the squash occur in their most destructive abundance, it will be necessary for protection against this borer to observe most of the following precautions, and, if possible, secure the cooperation of his neighbors in their observance:
(1) Not. to plant in or near infested ground.
(2) To plant early varieties for the protection of late squashes.
(3) To harrow infested fields lightly in fall and plow deeply in spring, to prevent the moths from issuing.
(4) To encourage the growth of secondary roots by covering the stems with earth.
(5) To destroy dead vines and old plants as soon as the crop is made.
(6) To keep the plants in vigorous condition, free from other insects and disease.
(7) To cut out such borers as may succeed in entering the vines in spite of the employment of other remedial measures.
The capture of the moths before egg deposition is also advisable.
Approved: JAMES WILSON, Secretary of Agriculture.
Wasuineton, D. C., July 17, 1908.
@As additional proof of the practicability of this, the writer refers to the testi- mony of Mr. J. V. D. Walker in Insect Life (Vol. LV, pp. 271, 272). [Cir. 38]
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