Europe, Asia
Prefers yellow toadflax (Linaria vulgaris) but has also been found attacking Dalmatian toadflax (L. dalmatica)
Rhinusa antirrhini and R. dieckmanni are morphologically very similar. The eggs are oval and flattened. Larvae are C-shaped, creamy yellow with dark brown head capsules, and are up to 4 mm long. Pupae are dark gray, typically 2½ mm long, and have two tiny ‘horns’ protruding from the top of the thorax. Adults are gray to black and covered in dense, short hairs. They have a long, distinctly curved, and pointed snout and a wide body. Adults collected from yellow toadflax, likely Rhinusa antirrhini, are typically 2½–3 mm long, while those developing on Dalmatian toadflax, likely R. dieckmanni, are up to 5 mm long.
Overwintering adults emerge in late spring and feed on toadflax shoot tips, leaf buds, and young leaves. As toadflax flowers open, adults feed on pollen and flower tissue. Females lay 40–50 eggs singly inside flower ovaries; this oviposition triggers the development of galls of enlarged seed tissue. Larvae feed on the modified seed tissue through three instars. Pupation occurs within seed capsules, with adults emerging in late summer or early fall to overwinter in plant litter. There is one generation per year.
Adult feeding on toadflax foliage and flowers is typically insignificant. Female’s egg deposition triggers the development of a spur (bump) on the seed capsule. The growing spur pushes the egg into the developing toadflax seeds, triggering the formation of a gall. The gall causes the 8–17 seeds closest to the egg to grow up to 10 times their normal size and turn a watery, pale yellow color. As a result, attacked capsules can be easily identified. Abnormal seeds are not viable, and larval feeding destroys additional seeds within attacked capsules. Decreasing seed output does not kill existing plants but can help reduce the rate of spread and genetic diversity of toadflax populations.
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