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Terellia virens
Diptera: Tephritidae
Terellia virens adult male. R.Richard
by R.F. Lang, USDA-APHIS-PPQ, Bozeman Biocontrol Facility, Forestry
Sciences Laboratory, Montana State University, Bozeman, MT 59717- 0278.
The seedhead fly, Terellia virens, a native of Europe, was approved
for release in 1992 and has been released in California, Colorado, Idaho,
Minnesota, Montana (recovered), Nebraska, Oregon (established), Washington,
and Wyoming (recovered).
Appearance
T. virens is a small (3-5 mm), clear winged, greenish-brown fly.
It has bright green eyes.
Habitat
Spotted knapweed ( Centaurea maculosa) is a weed species that
is found throughout the northern tier of states and as far south as Nebraska
and Virginia. This highly competitive weed favors and establishes quickly
on disturbed sites and overgrazed rangeland as well as established grassland
communities out competing the native vegetation. The release of T. virens
is part of a program to introduce a complex of spotted knapweed enemies
to help control this weed.
Pest Attacked
T. virens has been host tested against fifty-seven plant species.
The test results confirmed that T. virens has a limited host range
and a preference for species in the Centaurea subgenus Acrolophus.
Spotted knapweed ( C. maculosa ) is T. virens primary host.
There has been very limited attack on diffuse knapweed ( C. diffusa)
Life Cycle
The adult T. virens begin to emerge in late May. Weather conditions
determine if there will be two generations in a season. If so, most of
the second generation will overwinter in the seedheads of the mature plants
as prepupal larvae. Female T. virens lays her eggs in young, opening
flowers. Each female lays and average of 80 eggs which hatch within three
to five days after oviposition. The larval development to pupation takes
about fourteen days. The larvae spend their first two instars inside a
single seed. Later instars feed on mature and maturing seed. A seedhead
may be infested by one to seven T. virens larvae. The adult flies
are long lived and may live for forty-eight plus days.
Pesticide Susceptibility
Not yet known.
Commercial Availability
T. virens is not yet available from public or commercial sources.
Effectiveness
T. virens larvae cause considerable feeding damage on parts of
the seed. A test for germination viability of 500 seeds was conducted.
The control, no T. virens infestation, had 77.6% germination or
388 viable seeds compared to the T. virens infested seeds with 6.6%
germination or 33 viable seeds. T. virens is released as a part
of a complex of biocontrol agents for spotted knapweed will help control
the weed.
Conservation
Release sites should have the potential of being free from disturbance
such as development and pesticide use for at least ten years.
References
Groppe, K. and K. Marquardt. 1989. Terellia virens (Loew) (Diptera:
Tephritidae), a suitable candidate for the biological control of diffuse
and spotted knapweed in North America. Intl. Inst. of Biol. Control, DelÈmont,
Switzerland Final Report. 30 p.
MÅller-SchÑrer, H., C. Lehr, M. Klein, and K. Marquardt.
1991. Gel-electrophoretic description of European populations of Terellia
virens (Loew) (Diptera, Tephritidae): implications for its use as an
agent for the biological control of Centaurea spp. (Asteraceae)
in North America. Experientia 47: 859-864.
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editors of such use and cite the
author (if credited on the page you are using). A recommended form for citing this website is:
Weeden, C.R., A. M. Shelton, and M. P. Hoffman. Biological Control: A Guide to Natural Enemies in North America.
http://www.nysaes.cornell.edu/ent/biocontrol/ accessed (date).
Suggestions, corrections, and/or comments are appreciated: Contact
Tony Shelton (ams5@nysaes.cornell.edu).
http://www.nysaes.cornell.edu/ent/biocontrol/weedfeeders/terellia_virens.html
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