Hosts: Ponderosa pine and piñon
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.
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.
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