Biological Control Agent: Eteobalea intermediella Riedl.
Invasive Plant Species Attacked: Dalmatian toadflax (Linaria dalmatica (L.) Miller), yellow toadflax (L. vulgaris) and narrow-leaved Dalmatian toadflax (L. genistifolia spp. dalmatica).
Type of agent: Root feeding moth
Description and Biology
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.
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 25oC, 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 20oC, 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.
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
Unsuccessful rearing attempts were made using propagation tents between 1991 and 1998. No further attempts have been made.
Collection and redistribution methods
Not available for general distribution at this time.
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.
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.