Zotheca Tranquila: Cool Name for a Cute Caterpillar

Question:

What is a safe, non-chemical way of getting rid of this Zotheca tranquila caterpillar that infests my Mexican elder tree every spring?

- Ova L., Sierra County, NM

Answer:

John White, retired NMSU Extension Agent for Doña Ana County and the current garden curator at the UTEP Centennial Museum and Chihuahuan Desert Gardens in El Paso, TX, calls the Mexican elder (Sambucus mexicana) the “state tree of southern New Mexico.” This semi-evergreen is not as common in northern New Mexico, but it can be found in the Albuquerque area. The Mexican elder is native to the Southwest U.S. and Mexico, but more specifically to the regions’ arroyos, so they prefer more water in the home landscape and are not considered as xeric a plant species as, say, prickly pear or yucca.

Mexican elder tree (photo from www.desertblooms.nmsu.edu)

I reached out to NMSU Extension Entomology Specialist and NMDA State Entomologist, Dr. Carol Sutherland, for information on what she calls a “cute and unique” caterpillar:

Although rarely seen or “appreciated,” Zotheca tranquila is the only species in this unique genus in North America and the world. Apparently, there are numerous records of these insects from southern British Columbia, Canada, through California, with spotty (reported) records from farther east to the Texas Panhandle at least. The identification requests I have received through the years are primarily from southern New Mexico, where their host is a landscape tree/shrub.

Larvae are “hairless” yellow-, black-, and green-marked creatures with color patterns that vary among instars. Mature caterpillars can be just over an inch long. The pale gray-green moths with some “subtle patterns” on the wings are each about 3/4 inch long with a wing span of about 1 1/4 inches.

In our New Mexico communities, moths fly in early spring just as Mexican elder is leafing out. Moths fly and deposit eggs (singly) on new foliage at night, so you won’t see them or their minute eggs. How commonly they are sighted in New Mexico depends on tree owners’ observation skills.

Upon hatching, each larva starts rolling the leaf that will likely sustain their whole development. Probably they skeletonize that leaf in the beginning, but who’s looking that closely? With their host leaf still rolled and held in place with silk strands, really observant people might pick one of these leaves out of curiosity—it might be a little more dried-out looking or just curled up—and unroll it to find that “prize” inside. By this time, caterpillars should be at least half grown—or farther along.

You usually do not see them until they are mature and it is too late to control them with an insecticide or otherwise. Later treatments may kill the insects, but the damage is already done.

Damaged leaves on ornamental Mexican elders wither and fall, but the tree/shrub should replace them quickly. I don’t know of anyone that sprays for these insects. Getting an insecticide into the curled leaves would be a challenge. They are not responsible for chewing up the flowers—that’s another insect. And they aren’t responsible for the poor appearance—yellowish and frazzled—of Mexican elder in mid-summer. Mexican elder doesn’t tolerate high temperatures very well, but it can recover a bit later in fall.

There is only one generation per year in our lower elevations. I suspect that brand new adults emerge and fly at night—heading for the hills and mountains where they might find more native elderberry.

Thanks to Dr. Sutherland for all of that information, and thanks to you readers for sending in your gardening questions. Keep ‘em coming!

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

Links:

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!