Biological Control Agent: Eriophyes chondrillae Can.
Invasive Plant Species Attacked: Rush
skeletonweed (Chondrilla juncea)
Type of Agent: Gall forming mite
Status
Primary
Description and Biology
Adult:
Males are 0.16 to 0.18 mm long and females are 0.19 to 0.26 mm long. The yellow-orange,
soft bodied, worm-like adults have two pairs of legs. Full grown gall forming mites emerge
in the spring when the plant begins to bolt. Their feeding on the rapid spring growth
causes the plant cells to enlarge. Females begin oviposition when the plant buds begin
to swell, which usually occurs after five days. Each female will lay between 60 and 100
eggs into the gall they inhabit. Generally there are far more females than males.
To compensate for this disproportion, unfertilized females will go on to produce males, therefore,
increasing the opportunity for the females to encounter the males. As the galls dry,
the mites exit them and crawl to adjacent host plants or are wind blown to distant patches.
Multiple generations overlap, each completing every 10 days during the summer and continuing
until plant growth slows from declining moisture or fall frosts. Adults live 3 - 5 weeks.
Egg:
The eggs are spherical, 0.04 mm, and translucent when laid. During their short incubation
period the eggs change to pale orange.
Larva and pupa:
Eriophyes chondrillae develop through two nymph stages. The first stage measures
0.08 to 0.10 mm long, enlarging to 0.17 mm by the end of the second stage. Both nymph
stages are pale yellow-orange, have four legs, appear hump-backed and do not have genital openings.
Each gall can be infected with several hundred feeding mites in all stages.
Overwintering stage:
In its native distribution area in Europe, E. chondrillae overwinters as a non-feeding
adult. In Canada and the Pacific Northwest, they develop into a dark brown overwintering
stage (deutogyne), which results from early frost. The deutogynes travel downward on
the stem and remain in plant crevices or in the soil and are inactive until the following spring.
Location and effectiveness of attack
All stages of E. chondrillae attack axillary and terminal buds. Overwintering
adults attack spring bolting shoots and cause contorted leaf-like galls, which can expand to
5 cm. By the end of the growing season the galls will have generally destroyed the flower
buds, therefore, reducing seed production. Heavy attack creates deformed, stunted growth
and leaf yellowing. Eventually, the plant becomes a weak competitor. First year
rosettes and seedlings can be killed by E. chondrillae attack. Galls range from
1.5 - 2 cm diameter. On rare occasions, when conditions are ideal, galls have been known
to reach 3 - 5 cm diameter.
Predicted and native habitat
E. chondrillae accepts a wide variety of habitats wherever rush skeletonweed is found.
It readily establishes on south and west facing aspects where plants grow in undisturbed, well
drained soils.
E. chondrillae has an extensive native distribution in Europe. It occurs west
from Portugal, through central Mediterranean Europe, north to Germany, and east through the
most southerly portion of the former Soviet Union.
British Columbia Experiences
Origin:
The E. chondrillae released in BC is presumed to have evolved from a
variety found in south central Eurasia (South Caucasus also known as
Transcaucasus).
History:
In 1993, the first E. chondrillae treatments were made in the North
Okanagan. Releases continued until 1996 in the Okanagan and the central
Kootenays.
Habitat:
E. chondrillae releases are established and dispersed throughout the
north Okanangan and central Kootenays in the Interior Douglas-fir and Interior
cedar hemlock biogeoclimatic zones where
rush skeletonweed is found.
Field results:
A single release site near Passmore that was previously determined
established has not lately produced any galls. The plants growing here
exhibit a different growth habit and are being investigated to determine
if they are a different strain than the others found in the province.
With the exception of the site at Passmore, E. chondrillae has
self-dispersed and is widespread on the rush skeletonweed infestations growing
in BC. Puccinia chondrillina readily establishes to varying degrees
on the same plants with E. chondrillae. By late September, about 10% of the flowerheads
are distorted.
Not available for general distribution at this time.
Notes
E. chondrillae disperses freely within an infestation, but, usually requires distribution
assistance to become widely established.
References
Caresche, L. A. and A. J. Wapshere. No date. Biology and host specificity of
the Chondrilla gall mite Eriophyes chondrillae.
Harris, P. 2005. Classical biological control of weeds. Established biocontrol
agent Eriophyes chondrillae (G. Can). Bud gall mite. Gov. of Can. Agriculture
and Agri-Food Canada. July 19, 2007. http://res2.agr.ca/lethbridge/weedbio/agents/aeriocho_e.htm
MFR staff observations and comments.
Powell, G. W., A. Sturko, B. Wikeem and P. Harris. 1994. Field guide to the
biological control of weeds in British Columbia. B.C. Min. For. Res. Prog.
Rees, N. E., Quimbly, Jr., P. C., G. L. Piper, E. M. Coombs, C. E. Turner, N. R. Spencer,
L. V. Knutson (editors). 1996. Biological control of weeds in the west.
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