Japanese Superweed Meets its Match in Plant Louse

Invasive species have long been heralded as one of the ‘Big 3’ threats to modern biodiversity just after climate change and habitat destruction. These species are increasingly invading new habitats and out-competing the native species pushing them to extinction. In some cases, such as the now widespread Japanese knotweed, they can damage architecture and flood defences. This has earned this fast spreading plant the title as a ‘concrete cracking superweed’; costing the UK alone as much as £165 million a year.

The weed has rapid growth and can grow more than one metre a month in suitable conditions. The plants range has spread across North America and Europe and is even starting to advance to Australia. Its success can be attributed to its ability to thrive in a wide variety of environments, from building foundations to volcanic rock the plant lives on.

However, an unlikely hero has now appeared to hold back the advance of this persistent plant. The psyllid, Aphalara itadori, better known as a jumping plant louse looks to become the very first biological control for use against a weed approved by the EU. Having already undergone four years of trials, it has so far had promising results. Exposure to as few as 16 psyllids has been enough to cause one in 10 plants to die and stunted growth of the others.

So just how does this little creature pose such a danger to the weed. The adult insects lay their eggs on the leaves of the plant and the nymphs that hatch feed on the sap secreted by the plants halting their growth. Although this doesn’t always kill the plant directly it gives native plants the upper hand allowing them to dominate.

Biocontrol of invasive species has many times ended in disaster the most infamous example of this being the deliberate introduction of the cane toad to Australia to try to control populations of sugarcane eating beetles. Nearly 70 years on the cane toads are now the pest trying to be controlled.  However, testing of the psyllid so far has shown its limited diet will mean it won’t pose a threat to the native species. As release moves forward it is looking like we may have the first EU approved biocontrol agent and a chance of taking our buildings back.

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Madeleine Berry

Wildlife enthusiast and recent Biology graduate of Queen Mary, University of London.

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