Chapter XIV: Injurious Insects

While a number of different insects feed upon the asparagus plant, there are only two species which have so far become extensively distributed and caused serious damage in the United States. Both of these were imported from Europe, and are limited for their food supply to the asparagus plant.

THE COMMON ASPARAGUS BEETLE[A]

(_Crioceris asparagi_)

This beetle is by far the most important enemy of the asparagus plant. It was first noticed in this country at Astoria, L. I., now a part of New York City, in 1859, but its actual introduction into that locality occurred about 1856. The injury inflicted by this insect is due to the work of both adults and larvae upon the tender shoots, which they render unfit for market, early in the season. Later they destroy, by defoliation, growing plants, and are particularly injurious to seedlings, the roots of which are weakened by having their tops devoured. Larvae, as well as beetles, attack the tenderest portions of the plants, but the latter gnaw with seemingly equal relish the epidermis, or rind, of the stems. The beetles are also accused of gnawing young shoots beneath the surface, causing them to become woody and crooked in growth.

The beetle illustrated in Fig. 42 is a most beautiful creature--from the entomologist's point of view--slender and graceful in form, blue-black in color, with red thorax and lemon-yellow and dark blue elytra or wing covers, with reddish border. Its length is a trifle less than one-fourth of an inch.

_a_, beetle; _b_, egg; _c_, newly hatched larva; _d_, full-grown larva]

From the scene of its first colonization in Queen's County, N. Y., the insect migrated to the other truck-growing portions of Long Island. It soon reached southern Connecticut, and has now extended its range northward through Massachusetts to New Hampshire. Southward it has traveled through New Jersey, where it was first noticed in 1868, to southern Virginia. At present it is well established in the principal asparagus-growing sections of New England, of New Jersey, Delaware, and Maryland, and is present in Pennsylvania, New York, and Ohio. The question of distribution is an important one, as this species is rapidly extending its range. In a very few years we may expect its spread to other portions of the States in which it is now local, and later it will naturally move westward to Indiana and other States west and south of there.

The insect passes the winter in the beetle state under convenient shelter, and toward the end of April or early in May, according to locality, or at the season for cutting the asparagus for market, issues from its hibernating quarters and lays its eggs for the first brood. The eggs are deposited endwise upon the stem or foliage, and in the early spring upon the developed stalks, usually in rows of from two to six, or more. In from three to eight days the eggs hatch, the young larvae, commonly called "grubs" or "worms," presenting the appearance indicated in Fig. 42, _c_. They at once begin to feed, and are from ten days to a fortnight, according to Fitch and others, in attaining full growth. When full grown the larva appears as in Fig. 42, _d_. It is soft and fleshy, much wrinkled, and in color dark gray or olive, which usually becomes lighter and yellowish with age. The mature larva enters the earth, and here, within a little rounded, dirt-covered cocoon which it forms, the pupa state is assumed. In from five to eight or more days the adult beetle is produced, which soon issues from the ground in search of food and of a suitable place for the continuance of the species. In Fig. 43 is shown a spray of asparagus, with the common asparagus beetle in its different stages, asparagus top at the right showing eggs and injury.

The duration of the life cycle is about thirty days from the time the eggs are laid until the insects attain maturity, but the time is shorter in the hotter parts of a season than in the cooler days of May or September. In the District of Columbia the eggs, in the warmest part of midsummer, develop in three days and the pupae in five days. From this it may be estimated that, in the very warmest weather, the development of the insect may be effected in about three weeks from the time the egg is laid. In colder climates and in spring and autumn the development from egg to beetle will require from four to perhaps seven weeks. In the northern range of the species, two and perhaps three broods are usually produced, and farther southward there is a possibility of at least a fourth generation. In the latitude of the District of Columbia the beetles usually disappear to enter into hibernation in the latter days of September.

The common asparagus beetle has very efficient checks in the shape of predaceous insects, which prey upon its larvae and assist in preventing its undue increase. One of the most active of these predaceous insects is the spotted ladybird (_Megilla maculata_ DeG.), represented in its several stages in the illustration (Fig. 44.) The adult of this beetle is rose-colored, with numerous black spots. The spined soldier-bug (_Podisus spinosus_ Dal.) and the bordered soldier-bug (_Stiretrus anchorado_ Fab.) are also useful as destroyers of asparagus beetle larvae, which they catch and kill by impaling them upon their long beaks and sucking out their juices. Certain species of wasps and small dragon-flies also prey upon the larvae. Asparagus beetles are very susceptible to sudden changes of temperature, and immense numbers of hibernating beetles are sometimes killed in winter during severe cold spells following "open" weather.

_a_, larva; _b_, empty pupal skin; _c_, beetle, with enlarged antenna above]

_Remedies._--The common asparagus beetle, under ordinary circumstances, may be held in restraint by the simplest means. Chickens and ducks are efficient destroyers of the insect, and their services are often brought into requisition for this purpose. A practice that is in high favor among prominent asparagus growers is to cut down all plants, including volunteer growth, in early spring to force the beetles to deposit their eggs upon new shoots, which are then cut every day before the eggs have time to hatch. Another measure of value consists in permitting a portion of the shoots to grow and serve as lures for the beetles. Here they may be killed with insecticides, or the plants, after they become covered with eggs, may be cut down and burned, and other shoots be allowed to grow up as decoys. One of the best and least expensive remedies against the larvae is fresh air-slacked lime dusted on the plants in the early morning while the dew is on. It quickly destroys all the grubs with which it comes in contact. The lime may be conveniently applied by means of a whisk-broom or a Paris green sifter. Even dry road dust applied in this manner will have a beneficial effect. The special merit of these insecticides is that they can be used without the least danger upon young shoots being cut for market or home use.

Paris green and other arsenites, applied dry in powder, mixed with flour or plaster, or in solution, answer equally well, after cutting has ceased, and possess the advantage of destroying beetles as well as larvae. One pound of Paris green to a barrel of fine plaster makes a sufficiently strong mixture. It may be necessary to make two of these applications at intervals or as often as the larvae reappear on the plants. Powdered hellebore mixed with flour, one part to ten, or in solution of one ounce of hellebore to three gallons of water, is also very effective against the young larvae. Pyrethrum or buhach may be used in similar manner, and kerosene emulsion has been highly recommended by some experimenters. In hot weather, when the soil is dry, the larvae may be brushed or shaken from the plants so that they will drop to the heated ground, where they die, being unable to regain the shelter of the plants. Whichever methods for the destruction of this pest are adopted, unless the work be done thoroughly and with concerted action by all the growers in the section, the relief can not be permanent.

THE TWELVE-SPOTTED ASPARAGUS BEETLE

(_Crioceris 12-punctata_ Linn)

The presence of this insect in America was first detected in 1881, and it is still much rarer and consequently less injurious than the preceding species. In Europe, where it is apparently native, it is common but not especially destructive. The chief source of damage from this species is from the work of the hibernated beetles in early spring upon the young and edible asparagus shoots. Later beetles as well as larvae appear to feed exclusively upon the berries. The eggs are deposited singly, and apparently by preference, upon old plants toward the end of shoots, which, lower down, bear ripening berries, and they are attached along their sides instead of at one end, as in the case with the eggs of the common species. Soon after the larva hatches from the egg it finds its way to an asparagus berry, enters it, and feeds upon the pulp. In due time it leaves the first berry for another one, and when full growth is attained it deserts its last larval habitation and enters the earth, where it transforms to pupa and afterward to the adult beetle. The life cycle does not differ materially from that of the common species, and there are probably the same or nearly as many generations developed.

_a_, beetle; _b_, larva; _c_, second abdominal segment of larva; _d_, same of common asparagus beetle]

This species is at present distributed throughout the asparagus-growing country of New Jersey, particularly in the vicinity of the Delaware River, the whole of Delaware, nearly the entire state of Maryland, the District of Columbia, the southeastern portion of Pennsylvania bordering the state line of New Jersey, northeastern Virginia in the vicinity of the western shore of the Potomac River, Staten Island, and Monroe County, N. Y., the last mentioned being the most northern locality known for the species. The mature beetle in life rivals the common asparagus beetle in beauty, but may be distinguished by its much broader wing covers and its color. The ground color is orange red, each wing cover is marked with six black dots, and the knees and a portion of the under surface of the thorax are also marked with black, as seen in Fig. 45, _a_. The beetle as it appears on the plant when in fruit very closely resembles, at a little distance, a ripe asparagus berry. The full-grown larva is shown in Fig. 45, _b_. It measures, when extended, three-tenths of an inch, being of about the same proportions as the larva of the common species, but is readily separable by its ochraceous orange color. Fig. 45, _c_, shows the second abdominal segment of larva, and _d_ same of the common asparagus beetle, much enlarged.

_Remedies._--The remedies are those indicated for the common asparagus beetle, with the possible exception of caustic lime and other measures that are directed solely against that species, but the habit of the larva of living within the berry places it for that period beyond the reach of insecticides. The collection and destruction of the asparagus berries before ripening might be a solution of the problem, but it is questionable if recourse to this measure would be necessary, save in cases of an exceptional abundance of the insect.

THE ASPARAGUS MINER

(_Agromyza simplex_)

In a recent bulletin from the New York Experiment Station, Prof. F. A. Sirrine describes a comparatively new and injurious insect on asparagus. It was discovered on Long Island, and injures the young plants by mining just underneath the outside surface. The habits of this creature are such that there is little chance of applying remedies for its destruction. Cultural and preventive measures seem to be the most practical, and are suggested. The parent insect is a small fly, which deposits its eggs for the first brood early in June, and no doubt much can be done toward keeping the pest under control by not allowing small shoots to grow during the cutting season. Professor Sirrine is of the opinion that where young beds are put out yearly the pest can be kept in check by pulling and burning the old stalks. He points out the fact that the stalk should be pulled in the fall rather than in the spring, as it is difficult to pull them early in the season, and in many cases the dormant stage of the insect is left in the ground.

FOOTNOTES:

[A] Condensed from an official report by J. H. Chittenden of the United States Department of Agriculture.