Meet the Weevil that can Help Control Puncturevine

Pages 28 & 29

Meet the Weevil that can Help Control Puncturevine

By: Karen Fisher

Roak TenEyck hates goatheads. He hates pulling them out of his shoes, pulling them out of his kids' bicycle tires, and finding them tracked into his house.

When he heard about a weevil that eats nothing but puncturevine, the plant that produces goatheads, he wanted some for his yard. But when he called to make his order, he learned that the weevils, which were a success in California, Arizona and other southwestern states, weren't over-wintering in Oregon. He took a chance and ordered some anyway.

A few days later a package arrived with a mix of seed-eating and stem-eating puncturevine weevils. He turned them loose in his yard and hoped for the best.

TenEyck, who has always been fascinated with bugs, learned that the female seed-eating weevils lay their eggs in holes that they dig in the nutlike fruits of the puncturevines then cover them over with fecal matter.

When the eggs hatch, the larvae eat their way into the heart of the fruit where tow ot four seeds are stored in each of five sections. After feeding on the seeds, larvae pupate into adult weevils and eat their way out of the fruit to mate and produce more eggs -
up to 300 per female. The journey from egg to adult takes 25 days.

Puncturevine flowers turn into nutlike fruits with many sharp spikes.

Stem-eating weevils have a similar life cycle, but they lay their eggs in the stem, weakening the plant.

Every year Tribulus terestris, better know as "puncturevine," spreads its lush green tendrils and bright yellow blossoms over roadsides, fields, and public lands of our nation. They grow where nothing else will.

At first the plant may seem an attractive cover for unsightly land, but when you step on one of their skin-piercing, spiked fruits or flatten your bicycle tires repeatedly, you know they are not a welcome addition to the landscape.

All of those flowers turn into spiny burs that cause injury to the mouths and digestive tracts of livestock, are a nuisance to people, and diminish the value of hay and wool.

Puncturevines have not always grown in America. Legend says they traveled from the Mediterranean in the wool of sheep. Unfortunately, their natural enemies, Puncturevine weevils, didn't travel with them. In their natural habitat, Puncturevines and weevils have coexisted in manageable numbers for eons.

If the vines spread out of control, the population of weevils increase. When the weevils can't find enough plants to eat, their numbers diminish.

The spiny fruits of the puncturevine are painful to the skin, cause injury to the mouths of animals and cane even puncture auto tires.

The transplanted vines spread quickly throughout their adopted land, find a suitable habitat in the warmer winter areas of the southwestern states.

In 1961, puncturevine weevils from Italy were released in Clark County, Nevada, and Stanislaus County, California. Later releases followed throughout the western states.

According to Pam Geisel, Environmental Horticulture Farm

Puncturevine fruits separate into five segments. Each can carry two to four seeds. Their two prominent spikes give them the appearance of a goat's head, thus the name goatheads. They attach themselves to shoes, animal fur, or tires scattering seeds to distant places. Seeds can lie dormant in the soil for five years or more.

Advisor at the University of California, Davis:

The problem is that the introduced weevils did such a good job that they ate themselves out of house and home. As the population of puncturevine dropped off, so did the weevil population. Over time the seeds of puncturevine were able to accumulate and spread about without being controlled by the weevil, leading to another large-scale infestation.

"The good news," she continues, "is that the weevil population is beginning to catch up to the puncturevine. I've noticed that many of the seeds are heavily infested with weevils and the stems are also heavily infested in some areas. While that doesn't control this year's plant population, it will prevent or reduce the number of plants growing next year and in following years. Over time the number of plants will drop even further.

"However," she warns, "so will the weevil population and we will likely see the same roller coaster effect of up and down numbers of plants and weevils."

Ms. Geisel suggests maintaining a small planting of puncturevine as host for the weevils. Or you can introduce a new shipment of weevils when you notice the Puncturevine population spreading.
So what happened to the weevils. Roak TenEyck introduced into his yard seven years ago? Did they survive the Oregon Winters?

When an employee of the City of Umatilla came to order weevils for the city's streets and parks, TenEyck suggested they take a walk to inspect the city's puncturevines. They could hardly find a plant that didn't have a larva eating its seeds

Of the two types of weevils introduced to TenEyck's yard seven years ago, the seed-eating weevils have spread all over town. It appears that the stem-eating weevils haven't fared so well.

TenEyck is so excited about the possibility of controlling this hated plant the he makes a business of marketing weevils under the company name, I.R.V. Goatheads. He ships them out every Monday from he 1st of July to the end of September.

When an infested seed is opened, larvae begin to dance to avoid the sudden exporsure to sunlight. See for some awesome photos.

One of my biggest goals," say TenEyck, "is to make people aware of the problem so that even if they don't buy the weevils they will pull, spray, or do whatever it takes to get rid of that stuff"

"Gaining control of Puncturevine is a several year process," he warns. "Seeds can idle dormant in the earth for five years or more until favorable conditions cause them to sprout."

If you hate Goatheads as much as Roak TenEyck does, you may wish to add an order of weevils to your bag of tricks.

Roak TenEyck shows a puncturevine that is infested with Puncturevine Seed Weevils, Microlarinus Lareynii. They are so well controlled in Umatilla that we had to hunt awhile to find some plants.


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