What eats Japanese knotweed?


Learn about the challenges of controlling the invasive plant species Japanese knotweed and the potential solutions such as insects like the Japanese knotweed leaf beetle and the Japanese knotweed psyllid that feed on the plant as a biological control agent

The sap is irresistible to beetles

Japanese knotweed (Fallopia japonica) is an invasive plant species that can be difficult to control due to its ability to regrow from small fragments of the root system. There are currently no known animals that eat Japanese knotweed, as the plant’s tough stems and leaves are not palatable to most herbivores. However, some insects, such as the Japanese knotweed leaf beetle (Glyphuroplatus sachalinensis) and the Japanese knotweed stem and leaf miner (Acentropus lacordairii) have been found to feed on the plant. Additionally, the Japanese knotweed psyllid (Aphalara itadori) is a psyllid insect that feeds on the sap of Japanese knotweed, and is being researched as a potential biological control agent for the plant.

Aphalara itadori

The Japanese knotweed leaf beetle, Aphalara itadori, is native to Japan. It naturally occurs in Japan, where Japanese knotweed (Fallopia japonica) is also native. The beetle has coevolved with the plant, and in its native range, it helps to keep the growth of Japanese knotweed in balance. However, due to the invasive nature of Japanese knotweed in other parts of the world, the beetle has been introduced to certain regions as a biological control agent to manage the plant’s spread.

The Japanese knotweed leaf beetle, also known as Aphalara itadori, is a small insect that feeds on the leaves of Japanese knotweed (Fallopia japonica). It is a herbivorous beetle native to Japan and was introduced to several countries as a biological control agent to manage the invasive Japanese knotweed.

The beetle is about 3-4 millimeters in length and has a metallic bronze or dark green coloration. It has a distinctive appearance with a broad, flattened body and prominent antennae. The larvae of the beetle are pale and grub-like.

Japanese knotweed is a highly invasive plant species that can rapidly spread and dominate ecosystems, displacing native vegetation. The introduction of the Japanese knotweed leaf beetle was an attempt to control its growth. The beetle feeds on the leaves of the plant, causing defoliation and weakening the knotweed’s ability to grow and reproduce.

The life cycle of the beetle

The life cycle of the Japanese knotweed leaf beetle consists of four stages: egg, larva, pupa, and adult. After mating, the female beetle lays her eggs on the leaves of Japanese knotweed. The eggs hatch into larvae, which then feed on the plant’s foliage. As they grow, the larvae go through several instars before pupating. The pupal stage lasts for a few weeks, after which adult beetles emerge.

The Japanese knotweed leaf beetle has been successful in controlling the growth of Japanese knotweed in some areas. However, its effectiveness can vary depending on environmental conditions and the density of the knotweed population. In some cases, additional control measures may be necessary to manage the invasive plant effectively.

It’s worth noting that the introduction of any non-native species for biological control purposes should be carefully evaluated to prevent unintended ecological consequences. It is important to conduct thorough research and risk assessments to ensure that the introduced species will not pose a threat to native plants, animals, or ecosystems.

Acentropus lacordairii

Acentropus lacordairii is a species of beetle belonging to the family Cerambycidae, commonly known as longhorn beetles or longicorns. This beetle species is native to Europe and is primarily found in countries such as France, Italy, Spain, and Portugal.

Acentropus lacordairii is known for its distinctive appearance and long antennae, which are characteristic of longhorn beetles. The adult beetles are relatively large, typically measuring around 15 to 30 millimeters in length. They have a cylindrical body shape, with the head and pronotum usually covered in dense hairs or scales.

These beetles are active during the summer months and can be found in various habitats, including forests, woodlands, and grasslands. They are primarily associated with deciduous trees, such as oak, beech, and chestnut, as they feed on the bark and wood of these trees during their larval stage.

The life cycle of Acentropus lacordairii begins when the female beetle lays her eggs on the bark of suitable host trees. The eggs hatch into larvae, commonly referred to as “grubs,” which bore into the wood to feed and develop. The larval stage can last for several years, depending on environmental conditions and the quality of the food source. Once fully developed, the larvae pupate inside the wood, and after a period of time, the adult beetles emerge from the pupal cases.

Acentropus lacordairii is not considered a major pest species and generally does not cause significant damage to healthy trees. However, it is worth noting that the larvae of some longhorn beetles, including Acentropus lacordairii, can infest weakened or stressed trees, contributing to their decline.

As with many other beetle species, Acentropus lacordairii plays a role in natural ecosystems by contributing to nutrient cycling and serving as a food source for other organisms. While these beetles may not be particularly well-known or extensively studied, they are part of the diverse world of insects, adding to the richness of our natural environment.

In the UK, the use of Japanese knotweed as fodder for livestock is not widely practiced or recommended, mainly because the plant is considered invasive and its control and eradication are prioritized. However, there have been discussions and some studies on the potential use of Japanese knotweed as animal feed in general terms, due to its high nutrient content and rapid growth rate.

Japanese knotweed contains resveratrol, a compound that has been shown to have various health benefits, and it is rich in vitamins and minerals. This could theoretically make it a nutritious feed for livestock. Nonetheless, practical use of Japanese knotweed as livestock feed in the UK or elsewhere is limited by several factors:

  1. Invasive Status: Given its status as an invasive species, efforts are generally focused on controlling or eradicating Japanese knotweed rather than harvesting it for any use. There are legal implications regarding the disposal and spreading of Japanese knotweed that might limit its use as feed.
  2. Palatability and Safety: While some animals might eat Japanese knotweed if offered, the palatability and safety of the plant for different types of livestock have not been widely studied. Animals might or might not find the plant palatable, and the potential effects of long-term consumption are not well understood.
  3. Regulations: There are strict regulations in the UK regarding the handling and disposal of Japanese knotweed due to its invasive nature. Any use of the plant, including as feed, would need to comply with these regulations to prevent its spread.
  4. Lack of Research: There is a lack of extensive research on the effects of feeding Japanese knotweed to livestock. Without significant evidence to suggest it is beneficial and safe, it is unlikely to be adopted widely.

While there might be isolated instances or experimental studies examining the potential for Japanese knotweed as livestock feed, it is not a common practice in the UK or elsewhere, primarily due to the plant’s invasive status and the associated legal and environmental concerns. Efforts in the UK are more focused on controlling the spread of Japanese knotweed rather than finding uses for it.