Biological Control Agent: Eteobalea serratella Treitschke
Invasive Plant Species Attacked: Yellow toadflax (Linaria vulgaris), Dalmatian toadflax (L. dalmatica) and narrow-leaved Dalmatian toadflax (L. genistifolia spp. dalmatica)
Type of agent: Root feeding moth
Description and Biology
The moths have sender bodies measuring 8 – 9 mm long. Adults are black with yellow heads. Their black wings are covered with golden metallic flecks. Their normal wingspan of 16 – 18 mm decreases in crowded larval development conditions. Adults begin to emerge in early summer and live for about two weeks in the field (survival in the lab is up to four weeks). During this lifespan, they do not feed. Adults are weak fliers. Females emerge with up to 60 developed eggs and begin oviposition immediately. They will lay up to 180 eggs close to the stem base. The moths possess a good host finding ability, seeking new sites within short flights.
The white, 0.3 x 0.5 mm eggs change to yellow as they mature. Eteobalea serratella eggs have parallel lines (striate), differing from E. intermediella eggs which have a network of irregular meshing lines (reticulate). Eggs hatch in 9 – 10 days at 25oC, most frequently during the night or early mornings. Just prior to hatching, red eye spots can be seen inside the egg. E. serratella eggs show less susceptibility to fungal attack than E. intermediella.
Larva and pupa:
The newly hatched larvae bore into the plant at leaf axils or other soft tissue points where entry is easiest. The larvae move downward to the root, feeding into the root crown and on small roots. They can mine all parts of the roots. The tunnels are lined with a silken substance. Multiple larvae can develop on a single plant, but, the number depends on the plant and root size. Complete larval development takes 11 months and when mature they will be a maximum of 12 mm long. There is no rest period required for E. serratella as the larvae will continue to feed throughout the winter if temperatures and humidity are optimal. The larvae pupate within the silk tube. Excess soil moisture has a negative impact during larval development.
E. serratella overwinters in the larval stage, and will continue as long as ideal conditions are present.
Location and effectiveness of attack
The larval stages, notably the later instars, cause destructive control. Overall plant production is reduced when plants have been attacked by E. serratella. Seed weight is most significantly reduced and the flowering and seed producing periods are shortened. Continued attack reduces the plants’ ability to develop normally and, therefore, decreases new seedlings. In dry conditions yellow toadflax can be killed.
Predicted and native habitat
Potential suitable areas are grasslands, pastures, cropland and road or utility right-of-ways. E. serratella shows a preference for yellow toadflax over narrow-leaved Dalmatian toadflax.
In its native habitat, E. serratella’s locations are restricted to dry terrestrial sites, favouring the northern Eurasiatic areas that coincide with their host plant distribution.
British Columbia Experiences
Two unsuccessful attempts to propagate E. serratella moths on Dalmatian toadflax were made in 1992 and 1995. In 2004, yellow toadflax plants with infested roots were transplanted into a rearing tent. The site is currently under observation. To date, a few moths have been observed in subsequent years, however, the population has not increased.
Collection for redistribution
Not available for general distribution at this time.
E. serratella can exist with seed feeders Brachypterolus pulicarius and Rhinusa antirrhini (there is an adventive variety found on yellow toadflax). Yellow toadflax sites in south central BC should be treated with E. serratella from Rome, Italy.
Hansen, Rich. 2006. Biological control: a guide to natural enemies in North America. Eteobalea serratella Treitschke (Lepidoptera: Cosmopterygidae). November 28, 2006. http://www.nyaes.cornell.edu/ent/biocontrol/weedfeeders/eteobalea_serratella.html
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.
Saner, M. 1990. Impact of the root miner, Eteobalea serratella Tr. (Lep., Cosmopterigidae), on reproduction of the weed, Linaria vulgaris (Scrophulariaceae). In Proc. Symnp. Biol. Hung. 39:531-532
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, Switzerland. Final Report. 41 p.