SB 818 1 ipsgete > Marae C578 ENT 1O. 8, REVISED EDITION. Issued September 22, 1908. aited States Department of Agriculture, BUREAU OF ENTOMOLOGY, L. O. HOWARD, Entomologist and Chief of Bureau. THE IMPORTED ELM LEAF-BEETLE. (Galerucella luteola Mill.) By C. L. Maruatr, Entomologist and Assistant Chief of Bureau. GENERAL APPEARANCE AND METHOD OF WORK. The chief insect enemy of the elm is the imported elm leaf-beetle, the larve and adults of which frequently so disfigure the trees as to render them useless for shade and hideous rgther than ornamental. The beetle—a small, yellowish-brown insect—appears first and fills the leaves with small irregular holes, while the following broods of slug-like yellow and black larve skeletonize the leaves in irregular spots between the veins, working on both surfaces, but chiefly on the lower side, causing the leaves to assume a dry, brown appear- ance, to curl, and ultimately to fall. The second crop of leaves sent out by the trees in the southern range of the insect meets a similar fate. DISTRIBUTION. This leaf-beetle is a well-known defoliator of elm trees in Europe. It is especially abundant in France, southern Germany, and Austria, and to a lesser extent in Italy, Corsica, and Sardinia. It was brought to the United States about 1837 at Baltimore, Md., and gradually spread north and south until at present it reaches as far south as Richmond, Va., and as far north as southern New Hampshire on the Atlantic seaboard and Ithaca in central New York. For many years it confined itself to the Atlantic seaboard, but has now passed the Appalachian range and will probably spread through the West, conforming in general to the limits of the Upper Austral life zone. NATURAL HISTORY AND HABITS. CHARACTERISTICS OF DIFFERENT STAGES. The insect occurs on the trees in three different stages, and the fourth stage is passed on or under the surface of the ground at the base of the tree; i. e., the egg, larva, and beetle on the tree, the pupa in the ground. 53931—Cir. 8—08 rd ¥ 2 The adult, or beetle, is slightly over a quarter of an inch long, gen- erally of a yellowish or yellowish-brown color, with three somewhat indistinct brownish-black stripes on the wings. It is shown natural size at c, and enlarged at k, in figure 1. The eggs are placed on the lower side of the leaves in vertical clusters of from 5 to 20 or more eggs to each cluster, closely arranged in two or three irregular rows. They are oblong-oval in shape, tapering to a rather obtuse point, orange-yellow in color, and So Gi cay Q>: C2 bua th pat Sc Fic. 1.—EIm leaf-beetle (Galerucella luteola): a, e, Eggs; 6, g, larve; c, k, adults; f, sculpture of egg; h, side view of segment of larva; 7, dorsal view of same; j, pupa; J, portion of elytron of adult; a, b, c, natural size; g, j,k, somewhat enlarged; e, h, 7,1, much enlarged; f, highly magnified. (From Riley.) the exterior surface is covered with beautiful hexagonal reticula- tions. They are shown natural size on the leaf at a, and much enlarged at e, with the reticulated surface still more enlarged at f. The larva is elongate, reaching a length of about half an inch, and when newly hatched is nearly black. As it increases in size it be- comes, with each shedding of the skin, more distinctly marked with yellow, and when mature the yellow predominates, occurring as a broad dorsal stripe and two lateral stripes. The larva is represented natural size on the leaves, and somewhat enlarged at g, with por- tions still more enlarged at A and 7 in the figure. [Cir. 8] 3 The pupa is uniformly light orange-yellow, oval in shape, strongly ‘convex dorsally, and a little over a quarter of an inch in length. It is shown in the illustration at 7, enlarged. The egg stage lasts about a week, the larva normally fifteen to twenty days, and the pupa six to ten days. NUMBER OF BROODS AND DATES OF APPEARANCE. In the more southern range of this insect, including Maryland, Virginia, Delaware, and most of New Jersey, there are two broods annually, with an occasional smaller third generation. Farther north, including northern New Jersey, Long Island, New York State, and Connecticut, there is in general but one well-marked brood, with sometimes a supplemental or partial second brood. Throughout the double-brooded area the: beetles make their ap- pearance m spring about the middle of April, beginning to come out before the elms have put out their leaves, continuing on the trees through May, and perishing soon after egg-laying is finished. The eges of the first brood are deposited during May and into June, the larve of this brood occurring from early in May throughout June. Pupation takes place during June and July, and beetles of the second or summer brood emerge during July and into August. The eggs for the second brood of larve are deposited by these beetles from the middle of July throughout August, and the larve of the second brood skeletonize the second growth of elm leaves during the latter part of July and August, the later specimens occurring up to October. Pupation occurs chiefly during August and September, the beetles appearing from the last of August throughout September, and enter- ing winter quarters during September and October. In the single-brooded regions the beetles do not appear in spring until the last of May, and, in general, the periods are fully a month later for the different stages than in the southern districts, the beetles of the summer brood transforming most abundantly about the Ist of August. After feeding on the leaves a little while, and doing very inconsiderable damage, they go into winter quarters during August and September, remaining dormant eight or nine months. HABITS OF LARVA AND HIBERNATION OF ADULTS. The larvee from each batch of eggs feed together for a time, but ordinarily become separated and scattered later, especially with a scantiness of food. When full grown the larve usually crawl down the branches to the trunk and then to the ground, pupating almost immediately on or very near the surface of the soil about the base of the tree. They are apt to seek partial protection about grass bunches, but frequently accumulate in masses, exposed on the (Cir. 8] 4 surface in such a manner as to make a striking yellow carpet about the tree from a few inches to a foot or more wide. With very large elms, however, many of the larve are shaken off by winds or fall directly to the ground, sometimes fairly covering the surface over an area equal in diameter to the limb expanse-of the tree. Hibernation takes place in the adult state, both where there is but one brood and where there are two. For this purpose the beetles frequently enter houses and barns or outbuildings, sometimes assem- bling in such numbers that it is possible to collect them by the quart. They also enter cracks in posts, telegraph poles, fences, etc., or where- ever they can secure partial protection from winter storms. SUSCEPTIBILITY OF DIFFERENT ELMS. European elms seem to be especial favorites with this insect, and this would naturally be expected from its European origin. Its preference for the European elms is especially noticeable where these are grown in conjunction with American elms, the former being frequently entirely denuded, while the latter remain practically un- injured. In general, the coarser-leaved sorts of elms are distasteful to the beetles, and the smooth, thin-leaved varieties are especially subject to attack. The American species, Ulmus americana, is nota- bly exempt, and this, together with the general immunity of other American species, is a strong argument in favor of restricting planting to our native sorts. All species of elms, however, are attacked more or less, and in the absence of sufficient foliage of the favorite varie- ties the injury to less palatable sorts becomes almost equally marked. NATURAL ENEMIES. There are no effective American natural enemies of this insect. There exists in Europe an egg parasite which from time to time is very effective. This is a minute chalcidid, known as Tetrastichus xanthomelene Rond. After several years of fruitless effort this insect has been brought to the United States during the summer of 1908 by Doctor Howard, through the kindness of Professor Valery- Mayét, of Montpellier, France, and has been distributed at Cam- bridge, Mass.; Melrose Highlands, Mass.; New Brunswick, N. J.; Ithaca, N. Y., and Washington, D. C. It bids fair to become a strong assistant in the fight against the elm leaf-beetle. REMEDIES. In nearly every stage of its life history this insect is easily sub- ject to treatment. The best means against the adults and larve consist in the use of arsenical poisons in the form of sprays on the [Cir. 8] 5 foliage. The adults, for the week or two after emerging, feed on the newly expanded foliage, and a spraying with Paris green or other arsenical will destroy the great majority of them. Especial pains should be taken to accomplish the destruction of the insect in this stage, in order to prevent the partial disfigurement of the trees which will result if the matter be delayed until the larvee begin to appear. If rains interfere with spraying for the adults, or if it be neglected, the trees should be sprayed with arsenicals promptly on the first appearance of the larve, and the application perhaps renewed a week or ten days later, especially if rains have intervened. Paris green is the best arsenical, and may be safely used on elms at the rate of 1 pound to from 100 to 150 gallons of water. If London purple be used, an amount of lime equal to the poison in weight should _ be added to combine with any free arsenic and prevent scalding of foliage. The liquid should be applied by a strong force pump, a long hose, and a nozzle, such as the Vermorel or Nixon, which will make a fine mist-like spray. In spraying for the larve it is very essential to thoroughly wet the lower side of the leaves, on which they principally feed. In the case of the adults this is not so necessary, because they eat the entire substance of the leaf, and will get the poison from either side. On elms 15 or 20 feet in height the treatment can be made from the ground or from a wagon. For larger elms it will be necessary to climb the tree, using a hose from 50 to 100 feet long, and directing the spray by this means into the upper branches. By removing the spray tip from a large size Nixon nozzle, in order to get a direct dis- charge, the upper branches of comparatively tall trees may be reached and sprayed in a more or less satisfactory manner. In the case of very large elms in city parks or streets the use of stronger apparatus may be advisable, such as a fire engine or steam pump, and a larger nozzle, such as a graduating spray tip, capable of throwing either a direct stream or a spray. During spraying the poison should be constantly stirred to prevent it from settling to the bottom of the tank. The first effort should be to destroy the beetles and larve at their earliest appearance, to save the trees for the current year. Some- times, however, larve in the tops of tall trees will escape, and, when- ever from inefficient spraying or neglect they are allowed to reach maturity, a strong effort should be made to destroy the insect when it reaches the ground to transform, and thus limit or prevent dam- age from the second brood or in the following year. The congre- gating of the larve for pupation, frequently in enormous numbers, immediately about the base of the tree makes their destruction in this situation comparatively easy. This may be accomplished either [Cir. 8] 6 by wetting them with boiling water, or with kerosene emulsion diluted about four times. Frequently they may be collected by hand or shoveled up, and burned. - Remedial treatment is much simpler in the northern area of the range of this insect, where it is single-brooded, and becomes more difficult in the southern districts, where the number of broods is doubled and the appearance of the insect becomes somewhat irregu- lar, continuing practically throughout the summer. Approved: JAMES WILSON, Secretary of Agriculture. WasuineTon, D. C., August 31, 1908. [Cir. 8] O be . \ { ‘ - \ ® - * “a © AI ie og J al > ead eal i i Page ah me tater ay ee 7 SMITHSONIAN INSTITUTION LIBRARIES 01272 6634