Biological Control Agent: Eteobalea intermediella Riedl.
Type of agent: Root feeding moth
Status
Primary
Description and Biology
Adult:
Adults have yellow heads and black wings marked with gold metallic flecks. Their
normal wingspan is 16 to 18 mm, but, decreases when the plant roots become crowded during larval
development. The first adults emerge in the spring. Mating begins immediately after
adults appear. The females emerge with 60 developed eggs and may produce up to 180.
The eggs are oviposited in loose strings of three to eight into axils or on rough surfaces
on the soil within 10 cm of the plant. They remain non-feeding during their entire adult
life, which normally lasts two weeks in the field (up to 4 weeks in the lab). Adults
are weak fliers, taking short flights to seek host plants. In their native range, Eteobalea
intermediella are capable of two or more generations. When two generations occur,
the adults emerge in late spring. When multiple generations occur, the adults flight
period will overlap.
Egg:
The 0.3 x 0.5 mm white eggs have a network of irregular meshing lines (reticulate), differing
from E. serratella eggs which have parallel lines (striate). Incubation lasts 9
- 10 days at 25°C, changing from white to yellow. Most eggs hatch during the
night and early morning. Just prior to hatching, two red eye spots can be seen inside
the egg. E. intermediella eggs require high humidity and are more prone to fungal
attack than E. serratella.
Larva and pupa:
The newly hatched larvae move to leaf axils or other soft tissue points where entry is
easy. They can mine all parts of the roots. The feeding tunnels are lined with
a silken tube. Multiple larvae can develop on a single plant, but the number depends
on the plant and root size. In studies, up to 28 (19 larvae, three pupae and six pupae
casings) were present on narrow-leaved Dalmatian toadflax, whereas, only one or two were common
on yellow toadflax (this test plant study did not include Dalmatian toadflax). Pupation
occurs within the silk tunnel. When temperatures remain at 20°C, the new adults
emerge in 20 days. These will go on to produce a second generation of larvae which will
then overwinter. Excess soil moisture negatively impacts larval development.
Overwintering stage:
Second (or later) generation larvae overwinter in roots.
Location and effectiveness of attack
The feeding larvae, notably the later instars, consume and destroy a significant amount
of nutrient reserves, which reduce the upper vegetative and reproductive parts. Attacked
plants will produce fewer stalks, leading to decreased seedling production.
Predicted and native habitat
The distribution of Dalmatian toadflax growing in BC is beyond the native range for E.
intermediela and its most northern latitude limits, however, the climates are equivalent.
It is probable that E. intermediella will colonize Dalmatian toadflax in BC, however,
it is not expected to survive elsewhere in Canada. Preferred plants have a 4 mm diameter
root. Moist soils are not suitable.
In Europe, E. intermediella has a wide geographic range, is common within the Dalmatian
toadflax distribution and is frequently found throughout the western Mediterranean countries,
east to Iran, into southern Russia and central northern France.
British Columbia Experiences
Origin:
E. intermediella populations in BC originate from Serbia
(Yugoslavia).
History:
Unsuccessful rearing attempts were made using propagation tents between 1991
and 1998.
Habitat:
E. intermediella were released only into rearing tents in the
Bunchgrass biogeoclimatic zone. Long term populations did not develop and
no field releases have been made, therefore, habitat preferences cannot be
clearly defined at this time.
Propagation results:
In rearing tents, small populations persisted from 1999 until 2002. In
2004 the tents were dismantled after not seeing any further evidence of
survival.
Not available for general distribution at this time.
Notes
E. intermediella is proposed for Dalmatian toadflax sites in British Columbia and
south west Alberta.
It can exist with seed feeders Brachypterolus pulicarius and Rhinusa species.
E. intermediella populations from Novi Beograd, Yugoslavia may be best suited for
south central British Columbia.
References
MFR 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.
Saner, M., K. Groppe and P. Harris. 1990. Eteobalea intermediella Riedl
and E. serratella Treitschke (Lep., Cosmopterigidae), two suitable agents for the biological
control of yellow and Dalmatian toadflax in North America. Internat. Institute of Biolog.
Cont. European Station, Delemont, Switerland. Final Report. 41 p.
Saner, M. and D. Schroeder. 1988. Study and screening of Eteobalea serratella and E.intermediella ,
two candidate biological control agents of Dalmatian toadflax, Linaria dalmatica in British
Columbia. CAB Internat. Institute of Biolog. Cont. European Station Report.
Project Proposal. 12 p.
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