Amsterdam Takes a Punt on an Alien

There are many examples (e.g. the Cane toad, the Indian mongoose) of alien introductions, intended as agents of biocontrol, going wrong. So, it is with some trepidation that I read that Amsterdam is trying to 'cure' its problem with Japanese knotweed (Fallopia japonica) by changing the regulations to allow a mass release of alien Japanese knotweed psyllids (Aphalara itadori). Japanese knotweed, itself, was originally introduced by gardeners but now runs riot in many parts of Europe, where it cracks foundations and roads, as it grows. It also overshadows and kills natural vegetation, has no local herbivores and can rapidly invade new areas by sections of root or rhisomes left in the soil. The hope is that the sap-sucking 'fleas' will reduce the growth of Japanese knotweed and might even kill some young shoots (https://www.theguardian.com/world/2020/oct/23/amsterdam-releases-leaf-fleas-halt-japanese-knotweed-growth). All this sounds a bit optimistic (knotweed is very resistant) to me and the possibility remains that the psyllids will, in time, turn their attentions to other plants (I'm sure that tests have been carried out but the Dutch have a very wide array of crops and the psyllids might well be here for the long term).