Ips Species of the Eastern United States

From: USDA Forest Service. Insects of eastern forests. Misc. Publ. 1426. Washington, DC: USDA Forest Service; 1985. 608 p.

Among the bark beetles, the genus Ips ranks next in importance to the genus Dendroctonus in its destructiveness to pines and spruces. Infestations normally occur in lightning-struck trees and those recently felled by windfalls, snow-breakage, logging, and in road slash. However, when heavy populations develop in this material, the adults emerge and attack and kill adjacent groups of young healthy pines and the tops of older trees. Infestations in green timber are usually of short duration unless the trees have been weakened by drought, fire, or other disturbances. Spot- or group-killing in pulpwood or pole-size trees or, less often, in mature stands is characteristic of outbreaks. Widespread outbreaks occur frequently, and losses may be extremely severe. More than 3 million cubic meters of commercial timber and more than 1.8 billion cubic meters of pulpwood were killed in the South Atlantic and Coastal States during the period of 1952-55. It is estimated that annual losses of 765 million cubic meters of pulpwood are incurred in Florida alone. The North American species of Ips have been arranged into a number of taxonomic groups.

The male initiates the attack by boring through the bark to the wood and constructing a nuptial chamber. Here he is joined by one or more females (typically three), each of which excavates an egg gallery in the phloem. These galleries radiate in all directions from the chamber through the phloem, but eventually tend to run parallel with the grain of the wood. The resultant pattern tends to form a rough Y or I shape. Eggs are deposited in small niches at irregular intervals along the sides of the gallery, and the larvae tunnel in the phloem until fully grown. Pupation occurs in cells hollowed out in the inner bark. Young adults feed for a short time beneath the bark and then emerge, several often using the same exit hole. In northern areas, the winter is spent in the adult stage under the bark of the brood tree or in the litter below the infested tree. In the South, winter may be spent in the bark in all life stages.

Ips calligraphus (Germar), the six-spined engraver, occurs through Eastern America. Although it breeds in any species of pine available, its distribution in the Northeast coincides with that of pitch pine. Trunks, stumps, and large limbs of recently felled trees appear to be favored for breeding purposes, but the trunks of apparently healthy pines are also attacked, especially in the Southeastern States where it frequently attacks in concert with other Ips and Dendroctonus species. Attacks on living trees usually occur on the lower portions of trunks with diameters of 15 cm or more. In the South, this is one of the first species to attack drought-stressed trees.

The adult is dark reddish-brown to black and from 3.5 to 6.5 mm long. The declivity is deeply excavated and coarsely punctured. Each side is armed with six teeth, and the apical margin is strongly produced. The egg galleries, usually three to five, radiate from the central nuptial chamber and run longitudinally, grooving both the bark and wood. The larval mines are broad, tortuous, often long, and transverse. In the South, the life cycle may be completed in 25 days, and there may be 6 or more generations per year.

Ips grandicollis (Eichhoff), the southern pine engraver, occurs in Eastern Canada and in the Eastern United States from Massachusetts to Minnesota, Nebraska, and Texas and south to Florida and Mississippi. Like I. calligraphus, it attacks any pine species available but its distribution north of the southern pine region is coincident with the distribution of pitch pine. Recently felled trees and slash are preferred, but the trunks and limbs of apparently healthy trees are also infested when attack occurs in concert with other bark beetle species. Heaviest infestations in large living trees are found on limbs and the upper portions of trunks. Spot- or group-killing of pines is characteristic of the species. During periods of extreme drought, these groups increase in size and abundance. Populations normally develop in areas of recent logging operations.

The adult is dark reddish-brown to black and from 2.8 to 4.7 mm long. The declivity is deeply excavated, coarsely punctured, armed with five teeth at each side, and the apical margin is strongly produced. The egg galleries, three to five, radiate from a central nuptial chamber and run longitudinally, grooving both the bark and wood. The larval mines are more or less transverse. In the South, the life cycle requires from 20 to 25 days, and there are 6 or more generations per year.

The small southern pine engraver, I. avulsus (Eichhoff), the smallest species of Ips, breeds in all species of pines from southern Pennsylvania to Florida to Texas. Thin-barked slash, such as the limbs and tops, is preferred but groups of young, vigorous trees and the tops of large, living trees are also attacked frequently and killed. Attacks on large trees are usually associated with attacks on the lower portions of the trunks by other species of Ips or Dendroctonus frontalis. Adults are attracted to freshly cut and injured trees. Any disturbance that causes pitch flow may induce attack. Spot-killing occurs at times among pines showing no evidence of previous injury or decreased vitality.

The adult is reddish brown to black and about 2.3 to 2.8 mm long. The declivity is shallow excavated and deeply punctured. Each side is armed with four small teeth and the apical margin is slightly produced. Adults make one to several long winding egg galleries that originate from a central nuptial chamber. Larval galleries are short, transverse, and each ends in a pupal cell in the phloem. In the South, the life cycle may be completed in 18 to 25 days, and there may be 10 or more generations per year.

The pine engraver, I. pini (Say), occurs throughout most of the coniferous forests of North America except the Pacific Coastal forests, the southern pine forests, and Mexico. In the Eastern States it is ubiquitous in the north and extends south in the Appalachian Mountains to Georgia. It breeds in all species of pine and spruce within its range. Infestations usually develop in logging slash and windfalls or in trees dying of other causes. When heavy populations build up in this type of material, nearby healthy trees may be attacked and killed. Heavy infestations have occurred in cut-over and burned-over areas in Canada.

The adult is brown to black, is from 3.5 to 4.5 mm long, and has four teeth on each side of the declivity. Egg galleries, from three to six, radiate away from a central nuptial chamber in the phloem, deeply scarring the sapwood. Larval tunnels extend a short distance in the inner bark and end in pupal cells. Adults remain under the bark for a short period before emerging. While there, they make irregular, meandering food tunnels, deeply engraving the wood. Winter is spent in the adult stage on the ground. There appears to be three generations per year as far north as Wisconsin.

Other less common eastern species of Ips include: I. perturbatus (Eichhoff), the northern spruce engraver - breeds in white spruce in the Lake States and Canada; I. perroti Swaine - breeds in red and jack pines in Minnesota; I. borealis Swaine, the northern engraver - breeds in white spruce in Maine, Canada, and the Lake States; I. latidens (LeConte) - breeds in eastern white, red, jack, and Scotch pines; rarely in white spruce; and hemlock in New York, the Lake States, and adjacent parts of Canada.

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