Puncturevine / Weed Control User Tool (WeedCUT) / Methods for Managing Weeds in Wildlands

Overview

Two insects, the seed weevil (Microlarinus lareynii, Coleoptera: Curculionidae) and the stem weevil (M. lypriformis), have been introduced as biological control agents in California and are highly effective in reducing puncturevine.

These two weevils look very similar but attack different parts of the weed. Both species have multiple generations during the summer. Adults hibernate during the winter, hiding in surface vegetation and leaf litter. The seed weevil has a shorter proboscis (Figs. 1 & 2).

The seed weevil deposits eggs in holes chewed in the sides of immature fruits and covers them with a black secretion. Larvae feed on developing seeds and pupate inside the fruit (Fig. 3). Adults emerge through an exit hole and feed on stems, leaves, flowers, buds and fruits.

The stem weevil deposits eggs in the root crown or in the underside of stems. Larvae feed inside the stems and roots (Fig. 4), where they pupate. Emerging adults leave exit holes in the stems (Fig. 5).

Adults of both species cause minor defoliation, but larval damage to seeds and stems can be significant. For example, seed production decreased by 46% within 5 years after the first release in southern CA, and puncturevine coverage decreased by 70% to 100% in 5 of 6 regions studied during 15 years (Huffaker et al. 1983). Impact appears to be higher at non-irrigated sites, or when there is less precipitation. These weevils have substantially reduced the weed population in many areas of California and have been highly effective in Hawaii. However, it has been difficult to establish them at higher elevations and latitudes, presumably because of the negative effect of cold winter temperatures on adult survival. For example, the seed weevil established at only 1 of 5 sites where it was released in Lassen county, and the stem weevil failed to establish at any of these sites (Villegas and Gibbs 2010).

Larvae of the seed and stem weevils have been observed on Arizona poppy (Kallstroemia grandiflora) in Arizona, but no substantial non-target damage in the field has been reported.

Biological Control Agents

Species	Common name	Distribution	Impact	Notes
Microlarinus lareynii	seed weevil	moderate	high	First released in 1961 in CA
Microlarinus lypriformis	stem weevil	moderate	high	First released in 1961 in CA

How the Technique Is Employed

Some biological control agents are likely to be present at your site. Look for signs of weevils: adult feeding holes on leaves, stems and fruits. Presence of larvae and feeding damage inside fruits and stems. If they are present then there is no need to release additional insects.

Collect adult weevils in the field by vacuuming or hand collecting them from underneath plants. Infested plants and associated litter can be put in a paper bag and held to allow adults to emerge. Placing the bag in the sun for a short time to heat up stimulates adults to climb up the sides, making it easy to collect them.

Note that parasitic and predatory insects attack both species of weevils, so be carefult to collect only the adult weevils to release at another location to avoid spreading their natural enemies.

Special Tips

Weevils overwinter in leaf litter and other vegetation or debris, and under tree bark. Adults can live for long periods feeding on other plant species to survive, but they can only lay eggs after feeding on puncturevine and its close relatives, such as Kallstroemia species.

Biological control is probably most effective at areas that are dry and undisturbed (e.g., too difficult to access or too environmentally sensitive to treat with herbicides).

The adult weevils appear in the early summer on young puncturevine plants and they stop reproducing in late summer and fall. Try to apply alternate control methods, if desired, at times of the year when insects are not on the plants.

Caveats

The seed and stem weevils do not successfully overwinter north of Sacramento, so other methods should be applied there. Good level of control by these weevils occurs south of Sacramento.

Herbicides or other methods that kill puncturevine during summer will reduce the weevil population and disrupt biological control, but adults should be able to disperse and search for nearby plants that have not been treated.

Where Can I Get These?

Insects may be available from your county Agricultural Commissioner or CDFA.

References

Andres, L.A. and G.W. Angalet. 1963. Notes on the ecology and host specificity of Microlarinus lareynii and M. lypriformis (Coleoptera: Curculionidae) and the biological control of puncture vine, Tribulus terrestris. Journal of Economic Entomology 56: 333-340.

Huffaker, C.B., J. Hamai, and R.M. Nowierski. 1983. Biological control of puncturevine, Tribulus terrestris in California after twenty years of activity of introduced weevils. Entomophaga 28: 387-400.

Villegas, B. and C. Gibbs. 2010. Puncturevine, Tribulus terrestrisL. (Zygophyllaceae). In: D.M. Woods (ed.), Biological Control Program 2009 Annual Summary. California Department of Food and Agriculture, Plant Health and Pest Prevention Services, Sacramento, California. pp. 54-55.