Which plant-derived insecticide was used by the Romans to control lice?

The plant-derived insecticide used by the Romans to control lice is hellabore. Hellabore has a long history of use in traditional medicine and pest control. It is derived from plants in the genus Helleborus, which are known to contain compounds that can be toxic to various insects, including lice. The Romans utilized hellabore not only for its insecticidal properties but also for its purported medicinal benefits.

Sulfur was indeed used historically as a pesticide, but its primary application has been more for controlling fungal diseases rather than specific insect infestations like lice. Nicotine, while effective as an insecticide, was not as commonly documented in Roman times for this specific use against lice. Pyrethrum, sourced from chrysanthemum flowers, is a more modern insecticide that became widely used much later than the Roman period. Therefore, hellabore stands out as the specific choice associated with lice control during Roman times.