Bark Beetles
FIELD GUIDE TO INSECTS AND DISEASES OF ARIZONA AND NEW MEXICO FORESTS
Pine Engravers
Ips spp.

Hosts:  Ponderosa pine and piñon

Figure 90. Egg galleries of Ips pini on fire-damaged ponderosa pine. Note egg galleries radiate outward from centralized nuptial chamber.Symptoms/Signs:  In standing trees, fading tops of large trees or whole crowns in small trees can be indicators of Ips infestation. Other external evidence consists of accumulations of boring dust in bark crevices and at the base of the tree. Occasionally pitch tubes can be found on the trunk. Characteristic egg galleries may be found under the bark, slightly engraving the sapwood, hence the common name engraver beetle. In slash, look for boring dust and galleries.

Adults are small cylindrically shaped brown beetles a few millimeters in length. They possess a pronounced concavity at the rear end of the elytra that is bordered on either side by three to six tooth-like spines. Larvae are white, legless grubs.

Figure 91. Overwintering adult feeding galleries of Arizona fivespined ips on ponderosa pine log.Biology:  Beetles produce 2 to 4 generations per year, depending on climate, species, and elevation. In spring, adult beetles emerge from material infested the previous fall and fly to attack new hosts. Beetles prefer fresh debris from logging, construction activity or natural events, but during outbreaks living trees may be attacked.

Effects:  Bark beetles in this genus have the potential to kill thousands of pine trees during short-lived outbreaks in Arizona and New Mexico. Pine mortality is frequently noticed in drought years. Pinyon ips (I. confusus) killed millions of drought-stressed piñon across the Southwest from 2002 to 2004. Similarly, the pine engraver beetle (I. pini) and the Arizona five-spined ips (I. lecontei) killed millions of ponderosa pine during the same time span throughout Arizona. Some outbreaks are associated with human activities that create large amounts of fresh pine debris or that weaken trees. These insects are also beneficial, creating snags and providing a food source for other animals.

Figure 92. Adult Arizona fivespined ips beetle. Note spines along posterior edge of the elytral declivity.Similar Insects and Diseases:  Other bark beetles may be found in southwestern pines. They may be distinguished by egg gallery characteristics and adult appearance. Ips egg galleries possess a nuptial chamber—an enlarged excavated area—with one to many galleries radiating from it. The egg galleries are free of frass. Dendroctonus galleries vary by species in shape but lack the nuptial chamber and are packed with frass. Ips adults display a pronounced concavity at the rear end of the elytra, which contains three to six spines on either side. Dendroctonus adults on the other hand have a rounded declivity with no spines. Frequently, both Dendroctonus and Ips species occur within the same tree with Ips species typically located in the top half of the bole and Dendroctonus in the bottom half.

References:  24, 48, 52, 61, 75

Figure 93. Frass piles indicating Ips attacks on fresh ponderosa pine slash.
Figure 94. Ips species typically initiate attacks near the top of ponderosa pine causing a characteristic top-down fading pattern.
Figure 95. Stand level ponderosa pine mortality caused by Arizona fivespined ips on Prescott NF, Arizona.
Figure 96. Initial construction of egg galleries by pinyon ips on piñon.
Figure 97. Adult pinyon ips feeding colonies are frequently found near the base of piñon during the fall through early spring.
Figure 98. Pitch tubes caused by pinyon ips attacks.
Figure 99. Boring dust in bark crevices near base of pinyon ips attacked piñon.
Figure 100. Landscape level piñon mortality caused by pinyon ips in New Mexico.