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ODA works with USDA and other scientists who visit the original location of the weed to find natural enemies that can be tested as candidates for introduction as biocontrol agents in the US.
Before release in Oregon, agents are rigorously tested to ensure they are the following:
St. Johnswort Root Borer
Agrilus hyperici
Target Weed(s): St Johnswort
Toadflax Defoliating Moth
Calophasia lunula
Target Weed(s): Dalmatian and Yellow Toadflax
Tansy Ragwort Seed Head Fly
Botanophila seneciella
Target Weed(s): Tansy Ragwort
Toadflax Seed Capsule Beetle
Brachypterolus pulicarius
Spotted Knapweed Seed Head Fly
Chaetorellia acrolophi
Target Weed(s): Spotted knapweed
Field Bindweed Gall Mite
Aceria malherbae
Target Weed(s): Field Bindweed
Thistle Stem Mining Fly
Cheilosia grossa ( = corydon)
Target Weed(s): Musk, Italian and Slender Flower Thistles
Scotch Broom Seed Beetle
Bruchidius villosus
Target Weed(s): Scotch Broom
Russian Knapweed Gall Wasp
Aulacidea acroptilonica
Target Weed(s): Russian knapweed
Yellow Starthistle Peacock Fly
Chaetorellia australis
Target Weed(s): Yellow Starthistle
Knapweed Root Sulfur Moth
Agapeta zoegana
Target Weed(s): Spotted Knapweed and Diffuse Knapweed
Leafy Spurge Black Dot Flea Beetle
Aphthona nigriscutis
Target Weed(s): Leafy spurge
Russian Thistle Leaf Mining Moth
Coleophora klimeschiella
Target Weed(s): Russian Thistle
Leafy Spurge Brown Dot Flea Beetle
Aphthona cyparissiae
Russian Thistle Stem Mining Moth
Coleophora parthenica
Yellow Starthistle Bud Weevil
Bangasternus orientalis
Leafy Spurge Black Flea Beetle
Aphthona czwalinae
Rush Skeletonweed Gall Midge
Cystiphora schmidti
Target Weed(s): Rush skeletonweed
Knapweed Root Boring Weevil
Cyphocleonus achates
Target Weed(s): Spotted knapweed and Diffuse knapweed
Leafy Spurge Brown-Legged Flea Beetle
Aphthona lacertosa
Saltcedar Leaf Beetle
Diorhabda carinulata ( = elongata)
Target Weed(s): Saltcedar - Tamarisk
Leafy Spurge Copper Flea Beetle
Aphthona flava
Knapweed Broad-Nosed Seed Head Weevil
Bangasternus fausti
Target Weed(s): Diffuse, Spotted and Squarrose Knapweed
St. Johnswort Large Klamathweed Beetle
Chrysolina quadrigemina
St. Johnswort Small Klamathweed Beetle
Chrysolina hyperici
Yellow Starthistle Hairy Weevil
Eustenopus villosus
Rush Skeletonweed Root Boring Moth
Bradyrrhoa gilveolella
Gorse Seed Weevil
Exapion ulicis ( = Apion)
Target Weed(s): Gorse
Rush Skeletonweed Gall Mite
Aceria chondrillae ( = Eriophyes)
Scotch Broom Seed Weevil
Exapion fuscirostre ( = Apion)
Eurasian Watermilfoil Stem Mining Weevil
Euhrychiopsis lecontei
Target Weed(s): Eurasian Watermilfoil
Purple Loosestrife Golden Leaf Beetle
Galerucella pusilla
Target Weed(s): Purple Loosestrife
Purple Loosestrife Root Boring Weevil
Hylobius transversovittatus
Purple Loosestrife Black-Margined Leaf Beetle
Galerucella calmariensis
Knapweed Lesser Flower Weevil
Larinus minutus
Target Weed(s): Diffuse, Meadow, Spotted and Squarrose Knapweeds
Knapweed Blunt Flower Weevil
Larinus obtusus
Target Weed(s): Spotted and Meadow Knapweed
Tansy Ragwort Flea Beetle
Longitarsus jacobaeae
Yellow Starthistle Flower Weevil
Larinus curtis
Scotch Broom Twig Mining Moth
Leucoptera spartifoliella
Knapweed Sead Head Moth
Metzneria paucipunctella
Target Weed(s): Diffuse, Meadow, Spotted and Knapweeds
Dalmatian Toadflax Stem Boring Beetle
Mecinus janthiniformis
Target Weed(s): Dalmatian Toadflax
Puncturevine Seed Weevil
Microlarinus lareynii
Target Weed(s): Puncturevine
Puncturevine Stem Weevil
Microlarinus lypriformis
Purple Loosestrife Seed Capsule Weevil
Nanophyes marmoratus
Mediterranean Sage Crown Root Weevil
Phrydiuchus tau
Target Weed(s): Mediterranean Sage
Rush Skeletonweed Rust Fungus
Puccinia chondrillina
Knapweed Root Boring Grey-Winged Moth
Pterolonche inspersa
Target Weed(s): Diffuse and Spotted Knapweed
Dalmatian and Yellow Toadflax Seed Capsule Weevil
Rhinusa antirrhini ( = Gymnetron)
Knapweed Root Bronze Borer
Sphenoptera jugoslavica
Russian Knapweed Gall Nematode
Subanguina picridis
Gorse Spider Mite
Tetranychus lintearius
Thistle Crown-Root Weevil
Trichosirocalus horridus
Knapweed Green Clearwing Fly
Terellia virens
Target Weed(s): Spotted and Diffuse knapweed
Tansy Ragwort Cinnabar Moth
Tyria jacobaeae
Field Bindweed Defoliating Moth
Tyta luctuosa
Knapweed Banded Gall Fly
Urophora affinis
Target Weed(s): Diffuse, meadow, spotted and squarrose knapweeds
Canada Thistle Gall Fly
Urophora cardui
Target Weed(s): Canada Thistle
Knapweed UV Seed Head Fly
Urophora quadrifasciata
Target Weed(s): Diffuse, Meadow, Spotted, and Squarrose Knapweeds and Bachelors Button
Yellow Starthistle Seed Head Gall Fly
Urophora sirunaseva
Bull Thistle Seed Head Gall Fly
Urophora stylata
Target Weed(s): Bull Thistle
St. Johnswort Defoliating Moth
Aplocera plagiata
Canada Thistle Crown-Stem Weevil
Hadroplontus litura ( = Ceutorhynchus)
Leafy Spurge Defoliating Hawk Moth
Hyles euphorbiae
Russian Knapweed Gall Midge
Jaapiella ivannikovi
Yellow Starthistle Rust Fungus
Puccinia jaceae var. solstitialis
Leafy Spurge Stem Borer
Oberea erythrocephala
Canada Thistle Rust Fungus
Puccinia punctiformis
Target Weed(s): Canada thistle
Yellow Toadflax Stem Weevil
Mecinus janthinus
Target Weed(s): Yellow Toadflax
Whitetop gall mite
Aceria drabae
Target Weed(s): Whitetop Lepidium draba
Several hundred to a few thousand mites are found per infested plant. Mites feed on developing plant tissue that induces bud galls, fuzzy leaves, and thick curled leaves/stems. Damage results in stunting of the plant and reduces seed production. Infestation rates are variable from 1-3% in park settings to 60-95% in cultivated/disturbed sites.
Collect infested stems with galls late spring and place in direct contact with uninfested stems at new sites. Be careful not to move seed on gathered plants to new sites. As the old galls dry out, mites will migrate to fresh material. A softball sized clump of galled tissue is enough for a release.
Currently waiting on collectible Montana populations for first Oregon release. First field release was in Montana, 2019.
Petitioned for release in 2013 and permitted for release in 2018. Mites are tubular, white to orange, and microscopic. Mites are wind dispersed and sometimes carried on insects. Mites are widespread across Europe and Eurasia. Life cycle is 10 to 14 days. Mites goes through several generations per year. Mites migrate down to the roots as plants senesce during summer. Mites overwinter on root buds.
yellow starthistle root-crown weevil
Ceratapion basicorne
Target Weed(s): Yellow starthistle
Adults feed on and lay in leaves. Larvae mine down the leaf and feed in root crown. In lab setting, feeding could decrease plant size by 23%. Impact may be greater once introduced in the field where plants experience environmental stressors. 3-4 agents per plant on average. In the field, agents reduced seed fertility by 15%.
Overwintering adults emerge early spring and are collectable April-May. Adults can be aspirated from rosettes. Releases of 50 adults minimum. Current year adults emerge in June and spend mid-summer through winter in dormant state hiding in secluded places.
Native to Europe and SW Asia. Releases expecting in California in 2020 and Oregon in 2021.
Petitioned for release in 2006 and approved for release in 2019. Wide tolerance to climate. Spring adults lay a few eggs per day for 1-2 months before dying.
yellow toadflax shoot-galling weevil
Rhinusa pilosa
Target Weed(s): yellow toadflax
In experimental tests, galled plants produced 16% less above-ground biomass, 41% less below-ground biomass, 39% less flowering stems, and 58% fewer new stems, compared to control plants. Field observations concur on stunted shoots and flower prevention. Impacts in Oregon are not known.
Collecting adult weevils can be conducted in April-May when they can be sweep netted or aspirated from stems. Move in groups of 100 adults-200 adults.
Currently waiting on collectable Montana populations for first Oregon release.
Agents were first petitioned for release in 2013 and approved in 2018. The weevil is becoming rare in its native range (Serbia, Hungary, Romania) due to parasitism, lacking here in Oregon, so biocontrol releases may be important for the preservation of the species globally. Galls average 1x2 cm in size, 2.4 adults per gall and occur between middle and tip of stems. Adults overwinter in soil with one generation per year.
Gorse thrip
Sericothrips staphylinus
Thrips puncture plant cells and suck up contents. Feeding results in mottled white leaf spots. Thrips target new growth and can reduce flowering. In lab settings, thrips could stop seedling growth and kill it within 65 days, even at low thrip density. Small gorse bushes (1 ft) attacked were 25% smaller than healthy plants. Does not attack broom species.
Collectable year-round but best when warm weather brings fresh gorse growth and moved thrips will have time to recover before winter. Adult thrips can be knocked off branches and onto beating sheets with a stick, then aspirated into vials. Thrip covered branches can also be clipped, paper bagged sealed during transport, and infested branches tucked securely into new gorse site bushes. Be careful not to move predatory arthropods or seeds when collecting thrips. 300 thrips is the minimum release size.
Established as a biocontrol in New Zealand, Australia, and Hawaii. Native range throughout NW Europe. First releases in Oregon in 2020.
Adults are 1-2 mm long. Easily confused with flower thrips. Eggs laid in tender new stem growth. 76 eggs per female with 32-day life span as adults. Two generations per year are expected with peaks in June and August. Slow to spread, as winged forms are only produced at high thrip density and typically spread by walking or being blown onto neighboring plants.
Knotweed sap-sucking psyllid
Aphalara itadori
Target Weed(s): Knotweeds
Larvae and adults suck sap from phloem cells of leaves and stems. In lab settings, psyllids reduced attacked plant and root biomass by 50%. Feeding damages meristems and causes leaf curl where psyllids hide from predation. This depletes plant energy supply and reduces leaf area for photosynthesis.
Agents can be released in mid-April.
Petitioned for release in 2013 and permitted for release expected in 2020. One agent biotype from N. Japan prefers giant knotweed and another biotype from S. Japan prefers Japanese knotweed. 700 eggs per female laid on leaf surface. 33-day life cycle. One to three generations per year. Adults can fly and likely overwinter by seeking shelter in coniferous tree bark.
Biological control agent guide to common biological control agents found in Oregon.
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