Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. Contributien from the Bureau of Entomology L. OC. HOWARD, Chief Washington, D. C. PROFESSIONAL PAPER January 16, 1917 FLAT-HEADED BORERS AFFECTING FOREST TREES IN THE UNITED STATES. By H. E. Burks, Specialist in Forest Entomology, Forest Insect Investigations. CONTENTS. Page. Page. Importance of flat-headed borers.......-.... 1 | Agreement of adult and larval classifications . 4 OOM PLAN tS ere ese en see ee ees ae ee 2 | Distinguishing characters.................... 4 Character of the work.................--...- 2 | Key to genera of buprestid larvee............ 5 EAS INO AVS bic So ESO e I BEES En ae ee Eee 2 | List of genera, distribution, common habits, Seasonalhistonyecre. ee sessed. tee e ete 2 ANAM OS TUECCSereseee ee ease eerie 6 Specisithabitse rain es Beis eee ee 3 | References to important literature..........- 8 Special structural characters...............-. Shed IMPORTANCE OF FLAT-HEADED BORERS. Flat-headed borers (buprestid larva) are among the most important of the borers infesting forest trees in the United States. Some mine the leaves, one burrows into the cones, a number bore into the inner bark and outer wood of the trunk, branches, and roots, while the majority excavate oval winding ‘‘wormholes”’ throughout the sound or decaying sapwood and heartwood. At present the leaf-miners and the cone-burrower are not common enough to be important. The bark-borers often girdle and kill healthy trees or those injured by fire, floods, droughts, diseases, other insects, or careless lumbering, and at other times weaken trees so that they become easy victims of diseases, other insects, or unfavorable environ- ment. Sometimes when they do not kill-the tree outright their work - causes dead limbs or twigs, or serious defects, checks, or gum spots to form in the wood, or swollen galls to form on the branches. The wood-borers mine the sapwood and heartwood of the trunk, top, and larger branches and thus destroy or seriously injure a large amount of the tree’s most valuable product, its timber. Wormholes will cause the finest grade clear lumber to become unfit for the higher grade uses and therefore unsalable at the higher prices. 57169°—Bull, 437—17 4 BULLETIN 437, U. S. DEPARTMENT OF AGRICULTURE. FOOD PLANTS. Both deciduous and coniferous trees, as well as shrubs and herba- ceous plants, are attacked. Some genera attack only deciduous trees, some only conifers, while others attack both. Plants of any age may be attacked and any part of the plant from the roots to the leaves, but the principal part is the bark and wood of the main trunk. CHARACTER OF THE WORK. The borer work or injury consists of a flattened, oval, gradually enlarging, more or less tortuous mine or wormhole (Pl. VIII, figs. 1, 2), which, when completed, widens out into an elongate oval pupal cell. This cell connects with the outer surface by a short, oval exit hole. The mine has its surface marked by fine, transverse, crescentic lines and is usually tightly packed with arc-like layers of sawdust-like borings and pellets of woody excrement. The -injury may be entirely in the bark, entirely in the wood, or, as is usually the case, in both bark and wood. LIFE HISTORY. All bark and wood boring flat-headed borers hatch from eggs de- posited by the mother beetle singly or in a mass (PI. IX), on the bark © or tucked in some crevice in the bark or wood or under the bark at the edge of a wound. Each larva mines the inner bark or wood until it reaches maturity, when, after mining outward nearly to the surface, it retreats into its mine and forms an oval cell, in which it pupates and transforms to an adult beetle. The beetle rests awhile, then bites its way out, feeds on the bark, foliage, or pollen of some plant, usually its host, and then mates. The female, after depositing eggs to start a new generation, soon dies. SEASONAL HISTORY.! The egg is usually laid in the spring or summer and the borer — hatching from it feeds and rests until the following fall, or the second fall, or even the third fall, before it reaches maturity. It then | either rests over the winter in the larval stage and pupates and trans- forms to the adult the following spring, or it pupates and transforms to the adult in the summer or fall and rests over the winter in the adult stage in the pupal cell. Most of the bark-borers pass the winter in the larval stage and emerge soon after pupating and trans- | forming to adults in the spring. Many of the wood-borers pupate and transform to adults in the summer or fall and pass the winter ~ 1 Some evidence has been obtained which indicates that certain species may pass the winter in the egg ~ stage. Mr. A. B. Champlain collected a mass of eggs at Colorado Springs on February 12, 1914, which produced young Chalcophora larve. Certain Agrilus larve feed in the spring a short time before pupatings and transforming. Individuals of some species pass the winter in the pupal stage. No observation | have been made which would indicate that the adults live over the winter after they have emerged. FLAT-HEADED BORERS AFFECTING FOREST TREES. 3 in the adult stage before emerging. Feeding begins soon after emer- gence, and mating, egg-laying, and death soon follow, the whole being completed before the end of summer. SPECIAL HABITS. So far as known to the writer only two of our genera (Agrilus and_ Hupristocerus) cause the formation of galls (Pi. VIII, figs. 3, 6) on the host plant, and in these cases it seems to be more the special nature of the plant to produce the galls than it is the special work of the insect that causes them to be produced. Thus, the same species of insect will produce galls on some plants and not on others, or on one part of a plant and not on other parts of the same plant. A common western form, Agrilus, that infests the alder often pro- duces galls in eastern Oregon, while it seldom does so in eastern Cali- fornia. The common Agrilus bilineatus Web. of the Eastern States hardly ever produces galls, but it will do so sometimes when it works on the smaller branches of the oak. Besides the enlarged roughened galls, some species cause ‘‘splotch”’ mines to form in the bark of young shoots or branches. Chrysophana placida Lec. usually works in the heartwood of dead branches, tops, fire scars, etc., but recently Mr. P. D. Sergent found it mining the cones of the knobcone pine (Pinus attenuata) in southern Oregon (Pl. VIII, fig. 5). In pupating, it seems to be the most natural habit for the bark- borers to pupate in the bark, and most of them will do so if the bark is thick, but where it is thin they will go into the outer wood. The natural habit of the wood-borers is to pupate in the wood, but some ~ will pupate in the bark. . Although the usual food of the adults is the foliage of the host plant (Pl. VIIT, fig. 4), some are pollen feeders, and, as has been determined recently by Mr. F.C. Craighead, some will feed on the spores of fungi. In this instance the adult Agrilus bilineatus is of some benefit in de- stroying the spores of the destructive chestnut blight fungus. Mr. L. E. Ricksecker mentions (Entomologica Americana, 1885) having seen adult Melanophila consputa Lec. devouring scorched white ants (termites) on an old spruce log. SPECIAL STRUCTURAL CHARACTERS. The larve of the genus Agrilus (Pl. VI, fig. 2) and of the genus Eupristocerus (Pl. VI, fig. 1) bear on the thirteenth or last segment a pair of strong, heavily chitinized, toothed forks or forceps. These are absolutely distinct from any structure possessed by any other member of thefamily. Polycesta larve have a pair of sunken brown- ish spots on the head, one on each side of the jaws, a pair on the postero-dorsal surface of the third segment, and a pair on the antero- ventral surface of the fourth segment. The function of these spots 4 BULLETIN 437, U. S. DEPARTMENT OF AGRICULTURE. is unknown, but possibly it may be auricular. Thrincopyge larvee have a pair of brownish spots on the median subdorsal areas of the second and third segments which appear to be secondary spiracles. AGREEMENT OF ADULT AND LARVAL CLASSIFICATIONS. The buprestid larval classification agrees very well in the grosser features with that of the adults, except in the case of the genus Antharia. In adult classification this genus is placed between Melan- ophila and Chrysobothris, but its larval characters and life history indi- cate a much closer relation to Dicerca and its allies. The larval characters strongly indicate that the genus Buprestis should be split into three genera and the genus Melanophila into two genera. DISTINGUISHING CHARACTERS. The principal distinguishing character of the buprestid larva is the occurrence of a well developed ambulatory plate (Pls. I-VI) on both the dorsal and ventral surfaces of the first segment behind the head. Both plates closely resemble one another. Similar plates occur on some of the eucnemid larve (Pl. VII, figs. 1, 3), but the markings are different. The buprestids have a central line, groove, or V on the dorsal plate, while the eucnemids have two lateral lines. Cerambycid larvee (PI. VII, fig. 2) never have the ventral plate as well developed or similar to the dorsal. Cucujid larve (Pl. VII, fig. 4) are very flat, but they can be distinguished from the buprestids at once because of their well developed legs. Structurally there are two general types of buprestid larve: One (bark and wood borers) ‘‘flat-headed,’’ with a long slender subcy- lindrical tail; the other (leaf-miners) flattened, rather oval, deeply notched, and gradually tapering to the last segment. In the first type, the first segment, taken with the second and third and some- times the fourth, forms a broader, head-like division from the re- mainder, which, taken together, forms the long subcylindrical tail. In this type the first segment is much larger and broader than the others, while the thirteenth is usually much smaller. In the second type there is no distinct club head; the first and second segments are only a little narrower or a little broader than the third and fourth and the whole gradually tapers down to the thirteenth. Both types are distinguished by the following characters: Com- paratively small head more or less retracted into the first segment of a body composed of 13 fairly well defined, flattened segments; antennz medium-sized and three-jointed; ocelli wanting; labrum rather large, arched and protruded; mandibles short, strong, usually toothed and rather spoon-shaped; maxillz well developed; maxillary palpi two- jointed; labium well developed, arched, protruded; labial palpi minute and unsegmented, almost obsolete; first segment with a large, well-developed plate on both the ventral and the dorsal sur- Bul. 437, U. S. Dept. of Agriculture. PLATE lI. ASS cee Ps Sores mas Sate FLAT-HEADED BORERS. Fig. 1.—Chalcophora angulicollis: Larva. A, Dorsal view; B, dextral view; C, ventral view. X12. Fig. 2.—Chalcophorella campestris: Larva.