Zeuxidiplosis giardi
Klamath weed midge
(Diptera: Cecidomyiidae)

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zeuxidiposis giardi

Origin: This biological control agent originated in France. (1)

The Life Cycle:
Overwintering stages: As larva and pupa. (1)

Egg Stage: Eggs are laid on the leaves or stems.  A female will produce around 170 eggs, which are elongate, .33 mm (.012") long, and pale red.  Eggs hatch in about 12 days. (2)

Larval Stage: Newly emerged larvae enter the leaf bud and form galls.  Their feeding causes the leaves to grow together creating a hollow chamber or bivalved gall in which the 2 mm (.08 in), red-orange larvae develop.  Several larvae are often found within the gall.

Pupal Stage: Pupation occurs inside the gall.  Depending on the temperature and time of year, pupation may last from 6-20 days.  Pupae are yellow-red, but they may become darker as they mature. (2)

Adult Stage: The adults only survive for a few days.  The adults are very small and delicate.  They are gray flies that slightly resemble fungus gnats. (3)

Type of Damage to Host: The agent becomes destructive during the larval and pupal stage.  It produces leaf bud galls and leaf galls.  The feeding inside of the gall sometimes causes the weed to die.  The feeding causes the leaves to grow together.  The insect causes harm to a weed called St. Johnswort  (Hypericum perforatum).  Galls are formed on the leaves of the weed to create both protection and nutrition for the insect. (4,5)

Impact on the Host: The plant loses vigor, foliage, and root development.  Infected plants may die in the dry seasons due to their incapability to store and obtain moisture.  This agent reduces growth and seedling survival.  It has been successful only in Hawaii for controlling the weed, St. Johnswort.  (5)

Releasing of the Insect: The midge prefers damp locations with moderate to high relative humidity.  It does not do well in dry summers and windy areas.  It does not live in areas of much livestock.  You should transfer the midge in the larval stage when it is galled in the plants.  It was first introduced to the U.S. in 1951 in California.  It is now established in California, Oregon, and Hawaii. Releasing should not take more than three days. You should keep the roots wrapped in a moist paper towel. No storage is needed. (3)

Comments: There is apparently a larval resting stage during the summer and it is not known whether this is because of a type of dormancy or is heat related. It has been suggested that as the larvae feed, they inject a chemical substance into the sap of a plant (which causes the plant to form galls).  A large number of larvae feeding along the stem may cause death of the stem and root system.  In Hawaii, there has been a drastic decrease of the population of St. Johnswort in areas where the insect is established. (3)   Therefore, way to go gall midge! Keep up the good work!   It may be too cold and windy in most areas of Montana for this insect to do well but, that is not yet known. [Mr. Breitenfeldt]

(1) Wister, B. (1999, September). Klamath Weed Midge [on-line]. Available: <http://www.mcn.net/`rosebudweed/Klamath2.htm>.

(2) Rees, Naman, et. al., Ed, Biological Control of Weeds in the West, Western Society of Weed Science, in the cooperation with the USDA ARS, Montana Dept. of Ag., and MT State University, Color World Printers, Bozeman, MT, Feb. 1996. 

(3) Withers, T. (1999 August). Zeuxidiplosis Giardi [on-line]. Available: <http://www.bishop.hawaii.org/bishop/ento/Aocat/cecido.html>.

(4) Adam, Liberman. (11 Novenber, 2004). Zeuxidiplosis Giardi [on-line]. Available: <http://www.ento.csiro.au/aicn/system/c_1149.htm>.

(5) Los, W. (1999-2008). Zeuxidiplosis Giardi [on-line]. Available: <http://www.biolib.cz/en/taxon/id117067/>.

By: Justin Wehner.  3-2008. 

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