Dalmatian toadflax, Linaria dalmatica (L.) Mill. (Scrophulariaceae), a native to the eastern Mediterranean and Black Sea regions of Europe and Asia, has invaded over one million hectares in the western United States and Canada, in habitats similar to its native range. Once established, the aggressive vegetative growth of the plant allows it to invade undisturbed habitats where it can out-compete most other vegetation, placing native plant communities at risk.
Biological control of L. dalmatica with Mecinus janthinus Thomson (Coleoptera: Curculionidae) has shown promise in the field. In both studies reported in this paper, the presence of insect attack reduced L. dalmatica plant growth and reduced plant reproductive potential. In a field sleeve cage study, insect- attacked stems were significantly shorter (18 cm) and had 50-70% fewer fruits and flowers than the control stems at the end of the study period. M. janthinus attacked stems showed little apical growth, fewer fruits and flowers, and lower stem biomass relative to control stems. Similar results were observed in the potted plant study where the influence of the extensive root system of the plant was eliminated. This negative impact by the insect is caused both by adult feeding in the apical portion of the plant and the physical destruction of the plant stem from larvae feeding. The decrease in the insect-attacked stem heights may also have an impact on seed dispersal from the mature reproductive structures.
A combination of decreased seed production through M. janthinus biological control and poor seedling competition in the moisture limited sites common to north-central Washington State and other similarly dry habitats may negatively influence L. dalmatica populations more than general models predict.
Goulet, Elizabeth J.; Thaler, Jennifer; Ditommaso, Antonio; Schwarzländer, Mark; and Shields, Elson J.
"Impact of Mecinus Janthinus (Coleoptera: Curculionidae) on the Growth and Reproduction of Linaria Dalmatica (Scrophulariaceae),"
The Great Lakes Entomologist, vol 46
Available at: https://scholar.valpo.edu/tgle/vol46/iss1/5