|Adult cypress bark beetles are small, reddish brown to black, often shiny, and about 2-3 mm long (Figure 1). In weakened or stressed trees, adult beetles colonize the bole (trunk) and larger branches of the tree where they mate and lay eggs. Here, significant damage to the tree is caused by a 25-75 mm long, linear gallery (tunnel) with closely spaced niches at either side where eggs are laid.|
Figure 1. Close-up of a cypress bark beetle.
After the eggs hatch, the larvae (grubs) create new galleries which radiate outward from the central gallery (Figure 2). As they consume the inner bark (phloem), cambium, and outer sap-wood, the tree is girdled cutting off the flow of nutrients to the lower portion of the tree. Beetle colonization often causes top-kill and branch mortality, but can lead to tree mortality. Trees are colonized in the spring and summer. One generation per year is common, although more generations are possible during extended drought periods.
Newly emerged adults fly to a new host tree where they bore into small twigs a few inches from the branch tips. This kills the branch tip causing it to fade in color. The dead branch tip remains hanging on the tree (called "flagging") for a short period before breaking off. Upon close inspection of the branch tips, a hollow area can be seen where the beetle mined the twig (Figure 3). When beetle populations are high, hundreds of branch tips may accumulate on the ground.
Figure 2. Cypress bark beetle gallery in Arizona cypress trunk.
Figure 3. Arizona cypress twig mined by a cypress bark beetle.
Cultural practices can significantly reduce potential beetle colonization.
Dead and dying material should be pruned out of individual trees during
winter. Cut, dead, or down material should be promptly removed from the
area. Maintaining tree health and vigor will reduce the risk of beetle
colonization. This is accomplished in residential landscapes by slow,
deep, infrequent irrigation of susceptible trees species during extended
drought periods (April-June or longer) using a drip irrigation system
or a soaker hose placed at the drip line of the tree. Supplemental fertilization
is not generally recommended. New trees should be planted in the fall
if cypress bark beetles have
recently been active in the area.
Control is not practical once the bole of the tree is colonized. Some pesticides are labeled for prevention of bark beetles, but they are not recommended for use against cypress bark beetles. Healthy, vigorous trees can tolerate high levels of twig colonization and beetles will usually be unsuccessful in entering the trunk and limbs due to the tree's innate ability to exude pitch.
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Document located http://cals.arizona.edu/pubs/insects/az1316/
Published June 2003, Revised December 2011
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