''Aphalara itadori'', the Japanese knotweed psyllid, is a species of

psyllid Psyllidae, the jumping plant lice or psyllids, are a family of small plant-feeding insects that tend to be very host-specific, i.e. each plant-louse species only feeds on one plant species (monophagous) or feeds on a few closely related plants ( ...

from

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

which feeds on

Japanese knotweed ''Reynoutria japonica'', synonyms ''Fallopia japonica'' and ''Polygonum cuspidatum'', is a species of herbaceous perennial plant in the knotweed and buckwheat family Polygonaceae. Common names include Japanese knotweed and Asian knotweed. It is ...

(''Reynoutria japonica''). It has been licensed by the

UK Government ga, Rialtas a Shoilse gd, Riaghaltas a Mhòrachd , image = HM Government logo.svg , image_size = 220px , image2 = Royal Coat of Arms of the United Kingdom (HM Government).svg , image_size2 = 180px , caption = Royal Arms , date_es ...

for the

biological control Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

of Japanese knotweed in

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

; this was the first time that biological control of a weed was sanctioned in the

European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...

. The specific name comes from , the

Japanese Japanese may refer to: * Something from or related to Japan, an island country in East Asia * Japanese language, spoken mainly in Japan * Japanese people, the ethnic group that identifies with Japan through ancestry or culture ** Japanese diaspor ...

name for Japanese knotweed.

Introduction

''Aphalara itadori'' Shinji, is a species of

that specializes in feeding on ''

Reynoutria japonica ''Reynoutria japonica'', synonyms ''Fallopia japonica'' and ''Polygonum cuspidatum'', is a species of herbaceous perennial plant in the knotweed and buckwheat family Polygonaceae. Common names include Japanese knotweed and Asian knotweed. It is ...

'' (Japanese knotweed), as well as other ''Fallopia spp.'' / ''Polygonum cuspidatum'', such as ''

Reynoutria sachalinensis ''Reynoutria sachalinensis'' (giant knotweed or Sakhalin knotweed Japanese オオイタドリ ''ooitadori'', Russian Горец сахалинский, Гречиха сахалинская; syns. ''Polygonum sachalinense'', ''Fallopia sachalinen ...

/ Polygonum sachalinense'' (Giant knotweed) and '' Reynoutria x bohemica / Polygonum x bohemicum'' (Himalayan knotweed - the hybrid of giant and Japanese knotweed). Knotweed species' native home range is Asia. They were introduced to North America and Europe in the 1800s. Knotweed was carried from Asia to be used as an ornamental. Since these introductions knotweed species have spread throughout North America, Canada and Europe to establish themselves as a

noxious weed A noxious weed, harmful weed or injurious weed is a weed that has been designated by an agricultural or other governing authority as a plant that is injurious to agricultural or horticultural crops, natural habitats or ecosystems, or humans or liv ...

. Presently, 180 species of

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

exist that exhibit a predatorial behavior to ''Fallopia spp.''. ''Fallopia spp.'' are species of concern due to their aggressive nature and destruction they cause to

natural environment The natural environment or natural world encompasses all life, living and non-living things occurring nature, naturally, meaning in this case not Artificiality, artificial. The term is most often applied to the Earth or some parts of Earth. Th ...

s. Specifically, knotweed species have been seen to disrupt

riparian A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks ar ...

habitats and lead to the

degradation Degradation may refer to: Science * Degradation (geology), lowering of a fluvial surface by erosion * Degradation (telecommunications), of an electronic signal * Biodegradation of organic substances by living organisms * Environmental degradation ...

waterway A waterway is any navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other languages. A first distinction is necessary b ...

s they invade. Currently, ''Aphalara itadori'' is the only arthropod that has been extensively studied and proven to possess qualities needed in an effective

agent for the control of invasive knotweed species. Which is why it has been approved for release in the

. A four-year study in England and Wales found that the insects limited the growth of knotweed and did not breed successfully on ninety nearby native species, including the related species rhubarb, although it wasn't clear whether the insect colonies would be able to survive over the winter.The Independent - Japanese knotweed: Tiny insect could finally tame Britain's most invasive plant.
/ref>

Southern strain

The southern strain of ''Aphalara itadori'' is from Kyushu and is the strain released in the UK. Its home range is the

Kumamoto prefecture is a Prefectures of Japan, prefecture of Japan located on the island of Kyūshū. Kumamoto Prefecture has a population of 1,748,134 () and has a geographic area of . Kumamoto Prefecture borders Fukuoka Prefecture to the north, Ōita Prefecture to ...

, of the

Kyushu Island is the third-largest island of Japan's five main islands and the most southerly of the four largest islands ( i.e. excluding Okinawa). In the past, it has been known as , and . The historical regional name referred to Kyushu and its surroun ...

, in Southern Japan. The southern strain attacks Japanese and Bohemian knotweed.

Northern strain

The northern strain of ''Aphalara itadori'' comes from the northern island of

Hokkaido is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...

in Japan. This Hokkaido strain targets giant knotweed which can be found almost exclusively on the island of

Crossed strains

When the strains are crossed the ''Aphalara itadori'' individuals target all three species of knotweed (Giant, Japanese, and Himalayan).

Morphology

''Aphalara itadori'' grows from egg to adult in 5

nymph A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are ty ...

phases over 33 days at 23 °C. Overwintering adults survive in conifer tree bark. Once females are fully grown they can produce a mean of 637 eggs ± 121.96(±1SE, n = 11) with a mean period of production at 37.5 days ± 5.85 days (±1SE, n = 11). Adult psyllids can live up to 67 days.

Effects on knotweed

After extensive research, ''Aphalara itadori'' has been shown to defoliate knotweed species substantially. The psyllid individuals feed on the knotweed's

meristem The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...

. As a result of this feeding the leaves are left twisted and bound together. The

deformity A deformity, dysmorphism, or dysmorphic feature is a major abnormality of an organism that makes a part of the body appear or function differently than how it is supposed to. Causes Deformity can be caused by a variety of factors: *Arthritis an ...

caused by ''Aphalara itadori'' feeding reduces the photosynthetic rate, competitive ability, growth, and total leaf area. They deplete the energy supply of knotweed reducing the growth and root storage. This damage prevents the knotweed from growing back. Studies have indicated that ''A.itadori'' release would result in extensive ''Fallopia spp.'' defoliation on above and below-ground biomass. Grevstad et al., 2013, showed more than a 50% reduction in biomass after 50 days on ''F. sachalinensis'' and ''F. x bohemica''. However, A release would not be entirely risk free. Some individuals of ''A. itadori'' displayed characteristics of an ability to adapt and grow on non-target plants. However, the fitness level of these individuals was near zero and may result in behavioral avoidance instead.

References

{{Taxonbar, from=Q4779463 Aphalaridae Insects of Japan Insects used for control of invasive plants Insects described in 1938