Klamath weed midge
biological control agent
originated in France. (1)
The Life Cycle:
As larva and pupa. (1)
Eggs are laid on the leaves or stems. A
will produce around 170 eggs, which are elongate, .33 mm (.012") long,
pale red. Eggs hatch in about 12 days. (2)
Newly emerged larvae enter the leaf bud and form
Their feeding causes the leaves to grow together creating a hollow
or bivalved gall in which the 2 mm (.08 in), red-orange larvae
Several larvae are often found within the gall.
Pupation occurs inside the gall.
on the temperature and time of year, pupation may last from 6-20
Pupae are yellow-red, but they may become darker as they mature. (2)
The adults only survive for a few days.
adults are very small and delicate. They are gray flies that
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
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
nutrition for the insect. (4,5)
Impact on the Host: The plant
loses vigor, foliage, and
development. Infected plants may die in the dry seasons due to
incapability to store and obtain moisture. This agent reduces
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
moderate to high relative humidity. It does not do well in dry
and windy areas. It does not live in areas of much
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
It is now established in California, Oregon, and Hawaii. Releasing
not take more than three days. You should keep the roots wrapped in a
paper towel. No storage is needed. (3)
is apparently a larval resting stage
summer and it is not known whether this is because of a type of
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
to form galls). A large number of larvae feeding along the stem
cause death of the stem and root system. In Hawaii, there has
a drastic decrease of the population of St. Johnswort in areas where
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.
(1) Wister, B. (1999, September). Klamath Weed Midge [on-line].
(2) Rees, Naman, et. al., Ed, Biological Control of Weeds in
, Western Society of Weed Science, in the cooperation with the
USDA ARS, Montana Dept. of Ag., and MT State University, Color World
Bozeman, MT, Feb. 1996.
(3) Withers, T. (1999 August). Zeuxidiplosis
(11 Novenber, 2004). Zeuxidiplosis Giardi [on-line].
(5) Los, W. (1999-2008). Zeuxidiplosis