Insect and Disease Associates of the
Piiion-Juniper Woodlands
Terrence J. ~ o g e r s '
In order to successfully manage piflon-juniper ecosystems for
sustainability and social needs we must also look at and
understand the role of insects and diseases associated with this
ecosystem. At the present time, however, little is known about
the role of insects and diseases in the piilon-juniper ecosystem
This is not really surprising s h until just recently, last ten
years or so, the piilon-juniper type was managed primarily for
forage production with some considerations also being made for
fbelwood and piilon nut production With the advent of the
Forest Health Initiative and the Piilon-Juniper Initiative,
however, a more indepth understandq of the role insects and
diseases play in the piilon-juniper woodlands and their potential
impacts on management objectives is n e c e s q if we are to
manage this system for sustainability and desired social needs.
Insect activity in the piilon-juniper forest cover type appears
to be correlated with extended periods of drought which
predisposes large areas of host type to attack. During periods of
average Mall, insect activity in the piilon-juniper type is
usually undetectable. Drought acts as a "trigger" triggering
ecological processes which eventually leads to insect outbreaks
that often extend over thousands of acres of susceptible host
type.
Probably the most important group of insects associated with
the piiion-juniper ecosystem are the Ips bark beetles belonging
to the family Scolytidae. During extended periods of drought
Ips bark beetles (Ips mn@sus) often increase to outbreak levels
causing w i d e s p d tree mortality on thousands of acres of host
type.Mortality is often patchy consisting of small groups of five
to ten fading trees. In some cases, errtire viewsheds and
landscapes may be affected. Other Scolytidbark beetles affecting
piiton are the twig beetles. Twig beetles, Pityophthorus spp. and
Pityogenes spp., are frequent pests of piiion pines. Normally
they attack shaded-out and stormdamages twigs and b m h e s .
Occasionally, however, twig beetle populations locally build-up
in drought-stressed injured trees. When at out break levels, entire
viewsheds and landscapes can be affected.
'
Forest Pest Management, New Mexico Zone, USDA Forest
Se~dce,Southwestern Reg'on, Albuqueque, NM.
Outbreaks of the piiion needle miner, Coleotechnites
edulicola, and the piiion pine needle scale, Matsuwccus
acalyptus, also occur during periods of below average
precipitation levels and can cause widespread defoliation
damages to viewsheds and landscapes. Several years of heavy
defoliation damages can predispose infested trees to Ips bark
beetle attack and subsequent mortality.
Other incidental insects found associated with piilon include
the tiger moth, Halisidota ingens, the piflon sawfly, Zadigrion
spp., piilon spindle gall midge, Pifionia edulicola, bark moths,
Diorytria spp., and Vespamima spp., and the piiion pitch n d d e
moth, Petmva arizonensis.
Insects of note associated with junipers include the western
cedar borer, Trachykele blondeli, and the juniper twig pruner,
Styloms bicolor. The western cedar borer is an aggressive pest
of junipers and Arizona cyprus in New Mexico. It belongs to
the buprestid beetle group also known as metallic or flatheaded
wood borers. Unlike most other buprestids, the western cedar
borer will attack and seriously injure or kill seemingly healthy
trees. Considerable damage is found in some juniper stands;
older, larger trees appear to be favored by these beetles. The
juniper twig beetle, also found attacking junipers and Arizona
Cyprus causes twig dieback. This beetle belongs to the
cemmbycid beetle group also known as roundheaded wood
borers.
Unlike insect outbreaks which are generally cyclical and at
times cause seemu& spectacular damages and mortality across
viewsheds and landscapes, diseases are more insidious. That is
once a tree is infected with a disease pathogen, it may take years
before the symptoms appear and several r n m years before the
disease infected ttce dies. Mortality resulting from disease
infections is usually highest in young, immature trees.
Some diseases occurring in the piiion-juniper woodlands
include the mistletoes and mot rots. Mistletoes, Arceuthobiurn
divaricatum on piiion and Phoradenbon juniperinun on juniper,
are parasitic plants that injure and eventually kill their woody
hosts by stealing water and essential nutrients. Mistletoe plants
v q in color from yellow to green to red-green PiiIon pine
dwarf mistletoe plants consist of small conspicuous male and
female shoots approximately two to three inches in length
protrudrng through the bark of the infected branches. True
mistletoe plants very in length from a few inches to several feet.
Symptoms of infection include swelhg at infection sites, branch
dieback, and formation of witches' brooms. Dwarf mistletoes
spread by shooting seeds from explosive berries. True
mistletoes are spread by birds that eat the mistletoe berries.
Seeds pass through the birds unharmed and are spread in their
feces.
Root disease infected trees are mcult to diagnose since
symptoms above ground can resemble symptoms caused by
other insect and disease agents. Futhermore, little is known
about their affects within the pinon-juniper ecosystem. Only
recently have we observed and documented arnalleria root rot
killing pinon pines in northern New Mexico. Armillaria root
rot occurs in expanding pockets, often with mortality at the
center. The entire crowns of infected pifion saplings usually
turns reddish-brown all at once. Dieback, thinning foliage, or
yellowing of the crown is characteristicof older, infected pifion
trees. This disease spreads by means of spores and rhizomorphs.
When the fungus contacts the tree's root or root collar, it
penetrates the bark and enters the living tissue. Cellulose is
consumed leaving the root light-colored and causing the tree's
butt to rot.
In summary, there many insects and diseases associated
with the piflon-juniper woodlands. Their presence does not
mean they are a forest pest. As we intense our management
activities within the piiion-juniper woodlands, we will have
to monitor the impacts of resident insects and diseases to
determine (1) What kinds of damages are occurring, (2)
whether or not they are simcant, and (3) their impacts on
management objectives.