Europe
Common St. Johnswort (Hypericum perforatum)
Larvae are white with brown mouthparts, have inflated segments, and reach 11 mm in length. Adults are a metallic bronze color. Females are all one color while males’ heads are slighter greener than the rest of their bodies. Adults are flattened and tapered toward the rear and up to 5 mm long.
Larvae overwinter within common St. Johnswort roots and continue to feed within roots the following spring as plants bolt. Pupation occurs in the roots after the fourth instar. Adults emerge throughout summer as common St. Johnswort flowers, and they are most active in the heat of the day. Oviposition occurs near the base of common St. Johnswort plants in late summer. Newly emerging larvae burrow into the roots to feed and then overwinter. There is one generation per year.
When larvae feed within roots of common St. Johnswort, root tissue can be completely consumed. Stems arising from attacked roots and root crowns are stunted and produce fewer flowers; the attacked plant dies outright in some instances.
Randall, C.B., J.E. Andreas, J. Milan, and C.E. Moffat. 2024. Common St. Johnswort 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-2024-18-COMMON ST JOHNSWORT-A. https://bugwoodcloud.org/resource/files/33586.pdf