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Pelochrista medullana
Lepidoptera: Tortricidae

by L. Smith, USDA-ARS, Northern Plains Agricultural Research Laboratory, Sidney, MT 59270.

Pelochrista medullana (Stgr.) is a root-boring moth native to central Europe that was approved for release in the United States in 1984. European studies focused on eastern Austria and eastern Romania, but it is also thought to occur in Turkey and southern Russia. Limited numbers of P. inspersa have been released in Idaho, Montana, Oregon and British Columbia. There is no evidence of establishment in the United States.

Appearance

The adult is a tan to gray moth with mottled wings, measuring 8 mm in body length.

Habitat

Spotted and diffuse knapweed are invasive alien species that occur throughout the northern two-thirds of the contiguous United States. They are highly competitive weeds in semi-arid rangeland and Ponderosa Pine habitats, that establish quickly on disturbed sites and overgrazed rangeland. Both weeds can invade well-established grassland communities and displace the native vegetation. The release of P. medullana is part of a program to introduce a complex of natural enemies to help control these weeds.

Pests Attacked

P. medullana attacks spotted (Centaurea maculosa or C. biebersteinii) and diffuse knapweed (C. diffusa) in the rosette stage. Host specificity tests indicate that larvae can complete develop only on spotted and diffuse knapweed. They failed on other Centaurea species, including C. jacea, C. nigrescens, C. cyanus and C. macrocephala. The two native Centaurea spp., C. americana and C. rothrockii, are annuals which cannot support larvae, which must overwinter in the roots and complete development in the spring.

Life Cycle

P. medullana produces one generation per year. Adults emerge in July with a 1:1 sex ratio and live for about 2 weeks. Mating occurs within 24 hours of emergence, usually at dusk, and egg laying starts within 2-3 days. Eggs are laid primarily on the lower surface of rosette leaves. Females can lay up to 120 eggs in warm (18.4°C daily mean) dry weather, but this can be greatly reduced by cold (13.6°C) rainy weather. Release sites should have a mean temperature above 18°C for 3-4 weeks during the summer. Larvae hatch 7-9 days after oviposition and move to the center of the rosette and mine into the root crown. Larvae mine spiraling tunnels which are covered by a silk web in the root cortex, just under the epidermis, similar to Agapeta zoegana. Usually only one larva is found on an infested plant. P. medullana is known to coexist with A. zoegana, Cleonus piger and Apion spp. in Europe. Larvae overwinter in the roots and complete development in the spring.

Pesticide Susceptibility

Not known.

Commercial Availability

P. medullana is not yet available from public or commercial sources.

Effectiveness

Damage to the roots is similar to that caused by Agapeta zoegana. Only third- to sixth-instar larvae cause measurable damage, reducing root storage capacity and exposing the plant to pathogens. Small plants (< 5mm root diameter) are usually completely destroyed. Plants that survive insect attack are significantly smaller and produce fewer flower heads than uninfested plants.

Conservation

Sites that are chosen for P. medullana releases should not be disturbed for at least ten years by development or pesticide use.

For general information about conservation of natural enemies, see Conservation in the Tutorial section on this site, Feature Article on conservation in Volume II, No. 1 of Midwest Biological Control News.

References

Gassmann, A., D. Schroeder and H. Muller. 1982. Investigations on Pelochrista medullana (Stgr.) (Lep.: Tortricidae), a possible biocontrol agent of diffuse and spotted knapweed, Centaurea diffusa Lam., and C. maculosa Lam. (Compositae) in North America. Final Report, Commonw. Inst. Biol. Control, Delémont, Switzerland.

Müller, H. 1980. Annual project statement. Pelochrista medullana against diffuse knapweed. CIBC, Delémont, Switzerland.

Schroeder, D. 1981. Annual project statement. 2b. Pelochrista medullana. CIBC, Delémont, Switzerland.

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