Girdler Bug Attack: No Treatment Necessary
Southwest Yard and Garden
By Dr. Marisa Thompson & Dr. Carol Sutherland
Reprint from November 2017
Our mesquite trees are experiencing what appears to be a girdler
bug attack. This is the first time we have experienced this. How harmful are
they, and what can be done to rid these pests?
-
Jack D., Doña
Ana County, NM
Answer:
In order to answer your question,
I enlisted the help of NMSU Extension Horticulture Specialist and NM State
Entomologist, Dr. Carol Sutherland. Here is her response:
Yep. The culprit here is a type of
long-horned beetle known as the “mesquite girdler” (Oncideres rhodosticta).
Adults are about a half-inch long
and are several shades of dark gray, with dots or patches of rusty brown,
especially on their forewings. Their most obvious feature is the very long pair
of antennae, which is characteristic of most beetles in the Cerambycidae family.
The mesquite girdler is generally
found from Baja California probably into southern California, and from Arizona
to West Texas and south into Mexico, wherever potential woody hosts occur,
including mesquite, acacia, mimosa, palo verde,
and ebony. Honey mesquite may be the beetle’s preferred host and is where I have
seen the most activity.
Many of the beetles I’ve seen have
been resting on utility poles where security lights are located. On that kind
of background, they are far easier to spot than on mesquite twigs, where they
blend in well.
In natural settings, males can be
actively patrolling mesquite twigs where females are located. Females girdle
the host twigs before laying their eggs. I would think it makes more sense to
lay eggs below the girdle than above; above the girdle, everything is drying
up, probably too soon for the egg to hatch and larva to develop. Incubation and
larval feeding should take several months, at least. New adults should appear
next year.
Females are the ones that girdle
host plant twigs. These twigs will usually be about the diameter of one of your
fingers. When the beetle is viewed from the side, the axis of the body is at
right angles to the beetle’s head. The jaws are perfectly in position to bite
the bark; with each bite the female side-steps, going all the way around the
twig of choice. This cuts the vascular system leading to the end of the twig, causing
the leaves to soon fade and dry. As that happens, the girdled twig dries such
that if you pull on it, the twig breaks off cleanly at the girdle mark. Broken
twigs become part of the ground litter.
You can see this type of damage on
road-side mesquites from Las Cruces to Deming and beyond as well as from Deming
almost to Silver City. I-25 has had a nice display again this year from Las
Cruces almost to Truth or Consequences. There are probably other areas where
damage is noticeable, too.
Like other native insects,
populations of this Oncideres go up and down from year to year. This
year seems to be one of the “showier” years for beetle activity. Next year, the
mesquites will grow again, putting on new twigs and foliage. Mesquites are very
tough desert survivors with a variety of insects that feed and/or reproduce on
and in them.
No treatments are recommended or
needed for Oncideres in New Mexico. The beetles do not stay in an area
very long; flights and infestations are “hit or miss” from one year to the
next. Land managers hoping for mesquite control by these beetles are
disappointed. People with ornamental mesquites see the damage and fear the
worst, but, again, this is hit or miss from one year to the next. Developing
larvae are well protected by wood and bark.
As for these twig girdlers
attacking orchard trees, other species of Oncideres do that in different
parts of the country. In the eastern US, another species of Oncideres
girdles various fruit and shade trees. In extreme south Texas, still another Oncideres,
the “huisache girdler,” is associated with native acacias, both wild and
landscape trees.
Special thanks to Dr. Sutherland for answering
the question for this week’s column. Check out submitted photos of mesquite
girdler damage at https://nmsudesertblooms.blogspot.com/.
For more gardening information, including decades of archived
Southwest Yard & Garden columns, visit the NMSU Extension Horticulture page
(http://desertblooms.nmsu.edu/), follow us on social media
(@NMDesertBlooms), or contact your County Extension office (https://aces.nmsu.edu/county).
Marisa Thompson, PhD, is the
Extension Horticulture Specialist for New Mexico State University and is based
at the Agricultural Science Center at Los Lunas.
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