Europe, Asia
Dalmatian toadflax (Linaria dalmatica), yellow toadflax (L. vulgaris)
Eggs are pale yellow, strongly ribbed, and slightly conical. Larvae (caterpillars) are gray initially, but by the final instar, they are pale gray with vivid yellow stripes and black spots. Final instar larvae reach a maximum length of 4.6 cm. Pupae are reddish-brown within green cocoons made of silk and chewed leaves. Adults are a mottled gray-brown with light and dark markings on the wings and are 1–1½ cm long with a wingspan of 2½–3 cm.
Adult moths emerge in late spring and feed on the nectar of toadflaxes and other plant species. Females lay an average of 100 eggs singly on toadflax foliage and, less frequently, on toadflax flowers. Larvae feed on young, tender leaves but will consume older and tougher lower stem leaves as plants become increasingly defoliated. Larvae nearing the end of the fifth instar move to the base of toadflax plants and spin cocoons of silk, chewed leaves, and soil that they attach to stem bases, plant litter, or soil. There are 1–3 generations per year, depending on weather conditions and the length of the growing season. At northern latitudes and high elevations, 1–2 generations are most common; three may occur in warmer locales, at lower elevations, and in regions with longer growing seasons. The moth overwinters as a pupa within the cocoon.
Calophasia lunula caterpillars are known to feed and develop on plants related to toadflaxes, including nonnative ornamentals and one native North American species, Sairocarpus virga. Because C. lunula poses a risk to nontarget plant species in the USA, some land managers have ceased collection. Caution should be taken during its redistribution, especially in areas with desirable snapdragon species present.
Severe defoliation of seedlings and one-year-old plants can be fatal. Older, larger plants can usually rebound from defoliation, although defoliated plants are less vigorous and may produce fewer flowers. Complete defoliation of an entire patch of toadflax by this moth has not been documented.
Sing, S.E., R.A. De Clerck-Floate, C.B. Randall, and I. Toševski. 2022. Toadflax Biocontrol Agents: History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2022-29-TOADFLAXES-A. https://bugwoodcloud.org/resource/files/27419.pdf