Hosts or Prey
Puncturevine (Tribulus terrestris)
Identification
An obvious indication that these weevils are present is a round hole about 1/16 inch (1.5 mm) in diameter in the seedpods or stems of puncturevine. Feeding by larvae of puncturevine stem weevil, M. lypriformis, causes premature death and drying up of stems. Feeding by larvae of puncturevine seed weevil, M. lareynii, causes death of the seeds and premature browning and drop of seedpods. Adults of both species cause brown to grayish, sunken feeding scars on almost any aboveground part of puncturevine.
The adults are mottled brown, gray, and whitish weevils with an elongated, snoutlike head and mouthparts. Adults are about 1/5 inch (5 mm) long and covered with fine, pale, hairs. The oval egg is pale brown to yellow and 1/50 inch (0.5 mm) long.
Larvae and pupae occur hidden inside of puncturevine. The elongate larvae are distinctly segmented and pale orange to whitish with a brown head. The last (fourth) instar is about 1/5 inch (5 mm) long.
The pale orange to whitish pupa is oblong with distinct segments and about 1/6 inch (4 mm) long. As the pupa ages it develops distinct appendages folded against the body.
Life Cycle
Puncturevine weevils develop though four life stages: egg, larva, pupa, and adult. After hatching from an egg, larvae develop through four increasingly larger instars.
Adult puncturevine seed weevils deposit an egg in a pit they chew in immature seedpods of puncturevine. The hatching larva chews and feeds inside the seedpods, destroying the seed and surrounding tissue. This causes seedpods to prematurely turn brown and sometimes drop prematurely. The larva pupates in a cell inside the seedpod then the adult chews a round emergence hole.
Puncturevine stem weevil chews a hole in the matlike stems and root crown of puncture and deposits an egg in the hollow. The hatching larva mines and feeds inside the stem. At maturity, the larva pupates inside the stem then the adult chews a round hole through which it emerges. This weevil's feeding causes some stems to die prematurely and reduces the weed's ability to produce seed.
Both weevils overwinter as adults in organic litter on the ground or in protected locations of plants near where they fed. During the growing season adult puncturevine stem weevils live an average of 4 months during which a female lays an average of 250 eggs. The puncturevine seed weevil during the growing season lives an average of 3 months and each female lays about 200 eggs.
During the summer, weevil development time from an egg to a reproductive adult is about 1 month. The weevils have several generations per year.
Habitat
To provide classical biological control of puncturevine, entomologists from the University of California and the U.S. Department of Agriculture searched for and collected natural enemies of puncture from France, India, and Italy. Two Microlarinus weevils were collected then studied under quarantine. After they were found able to reproduce only on Tribulus species, which includes puncturevine, and on certain herbaceous caltrops (Kallstroemia species), the weevils were introduced into California and five other western states in 1961.
The weevils now occur throughout California wherever puncturevine grows. Although the stem weevil is slightly more effective than the seed weevil when each is used alone, the weevils are most effective if used together and where the puncturevine is moisture-stressed.
Unfortunately, two native parasitoids of the weevil larvae, Neocatolaccus tylodermae and Pteromalus (=Habrocytus) piercei (Pteromalidae), and certain predators, such as bigeyed bugs reduce the abundance and effectiveness of the weevils. Conversely preventing irrigation and water runoff from reaching puncturevine reduces its seed production and weed growth and increases the weed's mortality from weevil feeding. Overall the weevils' feeding has significantly reduced the weed's production of spiny seedpods in comparison with prior to the establishment of these weevils. And the percentage of land area covered by puncturevine has decreased.
Species
More than 1,000 weevil species occur in California. Microlarinus lareynii and M. lypriformis are exotic species and the only 2 Microlarinus species reported in California.
More Information
- Biological Control of Puncturevine, Tribulus terrestris in California After Twenty Years of Activity of Introduced Weevils, UC Berkeley, Entomophaga
- Biological Control: Pitting Insects Against Insects, California Agriculture
- Biology of Microlarinus lareynii (Col.: Curculionidae) on Puncturevine in Southern California, UC Riverside, Annals of the Entomological Society of America
- Biology of Microlarinus lypriformis (Col.: Curculionidae) on Puncturevine in Southern California, UC Riverside, Annals of the Entomological Society of America
- Descriptions of the Immature Stages of Imported Puncturevine Weevils, Microlarinus lareynii and M. lypriformis, UC Riverside, Annals of the Entomological Society of America
- Pest Notes: Puncturevine, UC Statewide Integrated Pest Management Program
- Puncturevine, Biological Control in the Western United States, UC Agriculture and Natural Resources
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Coleoptera
- Family: Curculionidae
