weed control efforts. By dissecting the stems Lance was able to find 30 – 100 adult weevils, Mecinus janthinus, in each stem! These 3mm long weevils are part of an old and oft-repeated story where an introduced pest species is reunited with the species that control it in its’ homeland – this is one form of what is called biocontrol. In this instance it will be a successful story from the initial release of 200 insects five years ago to the build up of a robust insect population – that actually kept the toadflax plants in the area of interest from flowering!
The toadflax plant population in the area may crash (good riddance to a noxious weed – but the weevils will have to seek new toadflax patches) or weevil and toadflax will persist at some low level. Either way control of an exploding non-native plant was achieved with a little help from the old country. This isn’t to say you should fear no weevil, Rhinocyllus conicus, a weevil introduced to control Carduus nutans is also a weevil with a taste for native thistles also and may have implications in restoration of Calephelis mutica, the swamp metalmark, as it reduces populations of this butterfly’s larval food plant.
In this instance, the weevil is hard working, hasn’t strayed from the task, and is capable of going places difficult to get to with a backpack sprayer of herbicide. It will be interesting to see what the future holds.