Figure 1. Extensive piñon mortality from piñon ips induced by drought conditions, Flagstaff, Arizona September, 2003.
Within the woodlands of 4,500’ to 7,000’ elevations in the Southwest, piñon pine occurs in association with juniper (Juniperus spp.) at the lower and ponderosa pine (Pinus ponderosa) at the higher elevations. Piñon are commonly utilized by a small bark beetle – piñon ips (Ips confusus). Since these beetles are from the Ips genus of bark beetles they are also known as engraver beetles. Piñon ips will utilize, Colorado piñon (P. edulis) and single leaf piñon (P. monophylla) and occasionally other pines in the Southwest. Juniper and ponderosa species that are generally associated with piñon are not affected by piñon ips. Junipers in these woodlands are attacked by cedar, cypress, or juniper bark beetles in the Phloeosinus genus and woodborers. Ponderosa pine is attacked by pine bark beetles in the genus Ips and Dendroctonus. For information on these insects, refer to az1316 "Cypress Bark Beetles" and az1300 "Pink Bark Beetles".
Twig beetles (Pityophthorus spp. and Pityogenes knechteli [Furniss and Carolin 2002]) are related to ips engraver beetles but they feed only on twigs and small branches and are not the primary agents of tree mortality. They feed under the bark in a similar fashion as Ips spp. of engraver beetles. Another insect that feeds on piñon are “pitch mass” borers (Dioryctria ponderosae), they cause copious amounts of pitch to flow from wounds and should not be confused with piñon ips.
Piñon ips is a native bark beetle that utilizes piñon pine inner bark and outer sapwood for food and to rear offspring, spending most of their lives underneath the bark of the tree. When a new generation of adults emerge from an infested tree, they are more likely to search for another live tree by flying a short distance (one to two miles maximum), unless insect populations are extremely high or tree population low. These bark beetles normally infest stressed, damaged and dying trees. They will also infest recently cut piñons and the slash associated with firewood harvesting or thinning practices during spring, summer, and fall. If enough beetles are produced by these practices, they can infest green standing trees, especially if they are stressed due to drought. Once the wood has dried sufficiently and the bark is easy to pry off, it is no longer suitable for bark beetle colonization.
Description
Piñon ips are cylindrical, about 5 mm (¼”) in length and shiny black to dark brown in color (Figure 2). A distinguishing feature of this beetle and other Ips species is a noticeable depression at the rear end that is bordered on each side with tooth-like spines. The piñon ips has five of these spines at the posterior end of their hardened forewings (elytra).
Figure 2. Adult piñon ips.
Tom DeGomez, Cooperative Extension
Life cycle
Male beetles initiate the infestation in spring by boring into the inner bark of the tree excavating a small (nuptial) chamber. Once the chamber is complete he releases chemical attractants that lure 2-4 females to the small chamber. Following mating, the adult females begin their tunneling in the inner bark and outer sapwood, forming their characteristic Y- or H-shaped galleries (Figure 3). Reddish boring dust is pushed out of the galleries through holes in the bark created by the adults, utilizing the depression found on their rear ends. Females lay eggs in niches along the side of the gallery. After the eggs hatch, the larvae (Figure 4) tunnel away from the egg galleries. The life cycle of the piñon ips is not fully understood. Most bark beetle larvae spend several weeks feeding on the inner bark. The mature larvae excavate oval shaped cells at the ends of their tunnels, where they pupate. Shortly after pupating they transform into the new adults completing their life cycle. It is believed that two or more generations are completed between March and late October, but up to 5 generations per year have been observed depending on drought severity and temperature. Adults overwinter underneath the bark, principally at the base of the tree in large groups. The first flight of the emerging adults the next spring occurs when the daytime temperatures begin averaging about 50 degrees F (16 degrees C) and will vary with elevation, slope and aspect.
Figure 3. Adult egg galleries, larval feeding galleries, and nuptial chamber on the outer sapwood (left) on the inner bark (right). Blue stain fungus surrounding the galleries.
Tom DeGomez, Coopeartive Extension and Bob Celaya, Arizona Sate Land Department
Figure 4. Larva inside gallery.
Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org
Figure 5. Rust-colored pitch tubes indicating a successful attack by bark beetles.
Signs of infestation
- Pitch tubes (Figure 5) (multiple small, reddish, popcornshaped masses of pitch) scattered up and down the trunk and branches that ooze out where the beetles enter the tree. These are usually rust-colored but yellow with time. The pitch is mixed with boring dust, or frass (see below). Pitch from physical wounds or “pitch mass” borers will be cream or amber colored.
- Frass or boring dust, that resembles fine sawdust (usually rust-colored but can be lighter) that collects in bark crevices, branch crotches, and on the ground around the base of the tree.
- Fading of foliage from green to straw-color, later turning red and then brown (beetles are probably no longer in the tree by this time). The tree will usually drop the dead needles one year after infestation.
- Blue-gray staining of sapwood under the bark by bluestain fungi introduced by the beetles (will not be evident on trees that were just recently attacked).
- Woodpeckers chipping away the bark to feed on the beetles beneath — does not always occur. Woodpecker activity will give the tree trunk and branches a reddish appearance due to the removal of the outer bark. The chipped off bark tends to pile up around the base of the tree.
- Live adults, pupae and/or larvae and their galleries (tunneling) can be found on the inner bark and lightly scoring the surface of the sapwood. Callow or immature adult beetles are tan to brown, while adults are brown to black, pupae are white, and larvae are white with brown heads
Management
Prevention is the best way to reduce losses due to piñon ips. Healthy, vigorous trees, growing on good sites usually are not attacked, unless there is a localized or widespread population buildup in the area. Trees affected by drought stress, disease, physical damage or are dying from other causes are typically the first piñon attacked. Piñons stressed and damaged by building construction activities are also very attractive to these beetles. Excavation for foundations, earth fills, paving, soil compaction and trunk wounds are some examples of tree stress and damage that attract these insects. This can be minimized or avoided if proper measures are employed before, during and after construction to reduce impact on the trees. Felled green trees left on the construction site also provide breeding material for the insect. Beetles may then proceed to infest adjacent live trees. For information on trees and construction refer to Colorado State University publication no. 7.420 "Protecting Trees During Construction".
Cutting during this time is not recommended, as fresh cuts and sap attract more beetles for as long as 6 months. If you must cut between March and October, remove or destroy all material. Options include:
- Grinding/chipping destroys larvae and dries the material quickly, rendering it useless.
- Immediately haul green material away, making sure the destination is more than 1 mile away from other pinons.
- Burn when safe and legal.
- Bury more than 8" below the soil.
- Bury the cut stump under 8" of soil.
- Debark large logs.
Bark beetles will usually inhabit a tree during the warmer months for 6 to 8 weeks. Round black exit holes indicate that the piñon ips has exited the tree. Other insects woodborers — large white segmented larvae or large beetles, some with long antennae) are commonly found in dead trees but they are generally not a threat to live trees.
Infested pines should be treated as soon as possible while the beetles are still within the tree, but the materials must be destroyed or removed. Trees from which the beetles have already exited do not need to be treated, but can be cut down and removed as time permits for use as firewood or to reduce wildfire and structural hazard. If the wood is dead, dry and not still infested, consider leaving some of the dead and down wood on the property to provide for a number of forest organisms critical to a healthy forest ecosystem. Material should be placed away from structures and trees, and downwind whenever possible
Under existing pines, avoid planting vegetation that requires frequent irrigation and fertilization, such as lawns, which is harmful to piñons. Consider slow, deep and infrequent (every 3 to 4 weeks) watering of stressed or damaged trees nearest your home. Start watering in May, or earlier at lower elevations, and continue until the monsoon season is well established.
Preventive spraying is only recommended for selected, high value trees around homes, businesses, recreation areas and other key areas during localized or widespread bark beetle activity, or if the tree(s) were disturbed during construction or other site disturbance activities. The insecticide label should indicate use for bark beetle prevention. These include varieties of carbaryl (trade name: Sevin 4F®) and permetherin (trade names: Astro™, etc.). The insecticide emamectin benzoate 4.0% (TREE-age®) is an injectable, systemic insecticide that is labeled for coniferous trees and recommended for pinon ips engraver beetles in pinon pines trees. Pinon pines, however are considered to be a highly resinous specious and it is therefore important to make sure that applicators quickly drill, plug and inject at trees in an individual manner, and not try to drill and plug multiple trees at a time. Further, it is crucial when using systemic products (those that travel through the vascular tissue of the tree) that tree are well-watered (either from rain or irrigation) before injection, as drought stressed trees will not translocate the product effectively.
Landowners can purchase and apply preventive insecticides themselves, or hire a certified pesticide applicator. Ideally, spraying should be done in March before the first beetles emerge to attack new trees but it can be done during any time beetles are actively attacking live trees (March-October). Be sure to read all instructions on the product label. Spray each year that is at risk of piñon ips attack, and spray only those trees which are uninfested. Preventive spraying will not save trees already infested or under attack by ips. Currently there is no proven pesticides to cure already infested trees this includes systemic injections that claim to kill beetles that are currently feeding in the tree. Additional information is available az1380 "Using Insecticides to Prevent Bark Beetle Attacks on Conifers".
Thinning
Thinning piñon-juniper woodlands can have substantial benefits. Thinning reduces competition for sunlight, nutrients, and moisture, hence enhancing the vigor of the remaining trees and making them more resistant to bark beetle attack. Reducing tree density will also significantly lower wildfire hazard, especially if the resulting slash (branches and tops less than 3” in diameter) is lopped and scattered (cut into short pieces and exposed to full sunlight), burned, or chipped and hauled away. When possible, thin or prune piñon during late fall, or winter, since ips are inactive at this time. If thinning or pruning must be done during the warmer months, high value piñon trees nearby may be preventively sprayed before starting and watered before and after thinning, and removal of the fresh slash away from the site is encouraged. Thinning is only effective in preventing future attack, thinning during an outbreak is an in-effective method of control.
Ecology
The main reason for increased activity by piñon ips may be due to the poor health of piñon-juniper woodlands. Negron and Wilson (2003) found that overly dense piñon stands led to reduced individual tree vigor and subsequently increased susceptibility to piñon ips. Many factors may have influenced increased stand density of piñon in the Southwest. These include previously favorable climatic conditions, and grazing by introduced ungulates which by removal of herbaceous plants would have improved conditions for trees and shrubs. There is also some evidence that historical fire patterns were interrupted due to removal of fine fuels by ungulates thus further favoring trees and shrubs (Gottfried et al. 1995, West and Young 2000).
During periods of endemic populations, piñon ips normally act as natural thinning agents infesting widely scattered trees that have been weakened or recently killed by other factors. They are an important ecological component in the recycling of nutrients back into the system for the utilization by other organisms. In addition, piñon ips can be a food source for woodpeckers and predatory beetles. Woodpeckers also create nesting cavities in the dead and dying piñons for themselves and secondary cavity nesting. And finally, wood-decaying fungi are provided a nutrient source for their survival and the decomposition of the trees.
Additional information
Cranshaw, W., and D.A. Leatherman. 2010. Ips beetles. Colorado State University publication no. 5.558. Ft. Collins, Colorado. http://www.ext.colostate.edu/pubs/insect/05558.html
DeGomez, T. E., C. J. Hayes, J. A. Anhold, J. D. McMillin, K. M. Clancy and P. P. Bosu. 2006. Evaluation of insecticides for protecting southwest ponderosa pine from attack by engraver beetles (Coleopera: Curculionidae: Scolytinae). Journal of Economic Entomology 99: 393-400.
DeGomez, T. 2006. Using Insecticides to Prevent Bark Beetle Attacks on Conifers. University of Arizona, College of Agriculture and Life Sciences Bulletin, AZ1380. Tucson, Arizona. http://hdl.handle.net/10150/144787
DeGomez, T. and B. Loomis. 2011. Firewood and bark beetles in the Southwest. University of Arizona, College of Agriculture and Life Sciences Bulletin, AZ1370. Tucson, Arizona. http://hdl.handle.net/10150/239575
DeGomez, T. and D. Young. 2009. Pine bark beetles. University of Arizona, College of Agriculture and Life Sciences Bulletin, AZ1300. Tucson, Arizona. http://hdl.handle.net/10150/146729
Dennis, C. and W.R. Jacobi. 2008. Protecting trees during construction. Colorado State University publication no. 7.420. Ft. Collins, Colorado. http://www.ext.colostate.edu/pubs/garden/07420.html
Furniss, R. L., and V. M. Carolin. 1977. Western forest insects. USDA For. Serv. Misc. Publ. 1339, Washington, D.C.
Gottfried, G., T.W. Swetnam, C.D. Allen, J.L. Betancourt, and A.L. Chung-MacCoubrey. 1995. Pinyon-Juniper woodlands. Pp. 95-132 in Finch, D.M., and J.A. Tainter (tech. eds.). Ecology, diversity, and sustainability of the Middle Rio Grande Basin. USDA Forest Service General Technical Report RM-GTR-286.
Keyes, C. Pinyon Engraver Beetle (Pinyon Ips Beetle. Utah Division of Forestry. Fire and State Lands, Forest Insect and Disease Leaflet. Salt Lake City, Ut. http://www.ffsl.utah.gov/foresthealth/insectdisease/pinyonengraverbeetle.pdf
Negrón, J.F., and J.L. Wilson. 2003. Attributes associated with probability of infestation by the piñon ips, Ips confusus (Coleoptera: Scolytidae), in piñon pine, Pinus edulis. Western North American Naturalist 63:440-451.
Schalau, J. 2003. Cypress bark beetles. University of Arizona, College of Agriculture and Life Sciences Bulletin, AZ1316. Tucson, Arizona. http://hdl.handle.net/10150/144794
Skelly, J. and J. Christopherson. 2003. Pinyon Pine Management Guide for Common Pests. University of Nevada, Cooperative Extension Bulletin EB03-02. Reno Nevada. http://www.unce.unr.edu/publications/files/nr/2003/EB0302.pdf
West, N.E., and J.A. Young. 2000. Intermountain valleys and lower mountain slopes. Pp. 255-284 in Barbour, M.A. and W.D. Billings (eds.). North American terrestrial vegetation, 2nd edition. Cambridge University Press. New York.