Bembecia chrysidiformis (Esper) [Lep.: Sesiidae] was examined for its natural history and specificity to Rumex spp. (Polygonaceae) which are weeds in Australia. Adults of this southern European insect appear in late spring to summer. Eggs are laid on the dried, seed bearing stems of perennial Rumex plants. The larvae tunnel inside the root during summer through to the next spring. In nature, the larvae are round in Rumex species of the subgenera Rumex and Acetosa. In host-specificity tests with 1st instar larvae, the roots of a number of genera within the Polygonaceae were attacked. Larvae died on a range of plants from other families except in Persea americana Miller (Lauraceae), Helianthemum nummularium (L.) Miller (Cistaceae) and Quercus ilex L. (Fagaceae) where larvae fed on the stems. The insect was judged safe for release in Australia by assessing aspects of its biology, its known host plants, and the lack of reported attack on other plants.