Posts Tagged: Euwallacea

Polyphagous and Kuroshio Shot Hole Borers

FUSARIUM DIEBACK AND POLYPHAGOUS SHOT HOLE BORER ON AVOCADO

Akif Eskalen¹, Richard Stouthamer²

¹Department of Plant Pathology and Microbiology, UC Riverside

²Department of Entomology, UC Riverside

 

BACKROUND

Polyphagous shot hole borer (PSHB), Euwallacea sp. (#1) (Fig.1) is an invasive beetle that carries three fungal symbionts in a special structure in their mouth called a mycangium.  These symbiotic fungi are Fusarium euwallaceae, Graphium euwallaceae and Acremonium pembeum (Freeman et al. 2013, Lynch et al. 2015). The adult female tunnels galleries into a wide variety of host trees, where it lays its eggs and grows the fungi (Fig.2, 3). The fungi cause the Fusarium Dieback (FD) disease, which interrupts the transport of water and nutrients in over 38 tree species that are suitable for beetle reproduction. A separate invasion was recently detected in San Diego county and is now being called Kuroshio shot hole borer (KSHB) and is another closely related species to PSHB (Euwallacea sp. (#5)) carrying two new fungal species - Fusarium and Graphium. Both species have been found causing damage on avocado in the los Angeles basin and San Diego County.

 

BEETLE BIOLOGY

Adult females of PSHB and KSHB (Fig. 1) are black in color and 1.8-2.5 mm long. Adult males (Fig. 4 ) are brown and smaller than females at 1.5 mm long. More females are produced than males, which are flightless and very rarely leave the galleries. Mature siblings mate with each other so that females are already pregnant when they leave to start their own galleries. Males do not fly, but stay in the host tree.

 

SYMPTOM AND SIGNS

External Symptoms: Attack symptoms, a host tree's visible response to stress, vary among host species. Staining (Fig. 5), sugary exudate ( also called a sugar volcano) (Fig. 6-7), gumming (Fig.8), and/or frass (Fig. 9) may be noticeable before seeing the tiny beetles. Beneath or near these symptoms, you may also see the beetle's entry/exit holes, which are ~0.85 mm in diameter Fig 10). The abdomen of the female beetle can sometimes be seen sticking out of the hole. Advanced fungal infections will eventually lead to branch dieback, as seen on this Avocado (Fig. 11).

 

Internal Symptoms: Fungal species associated with the beetle PSHB and KSHB cause brown to black discoloration in infected wood. Discolored wood can easily be seen when bark is scraped away around the entry/exit hole (Fig 10). Cross-sections of cut branches (Fig. 12) show the extent of infection.

 

KNOWN REPRODUCTIVE HOSTS OF PSHB and KSHB

PSHB attacks hundreds of tree species, but it can only successfully lay its eggs and/or grow the fungi in certain hosts.

Known Suitable Reproductive Host Trees of PSHB:             

1. Avocado (Persea americana)
2. Box elder (Acer negundo)
3. California Sycamore (Platanus racemosa) 
4. Big leaf maple (Acer macrophyllum)  
5. Evergreen Maple (Acer paxii)  
6. Trident maple (Acer buergerianum)
7. Japanese maple (Acer palmatum)  
8. Castor bean (Ricinus communis)  
9. Mexican sycamore (Platanus mexicana)
10. Red Willow (Salix laevigata)
11. Mimosa (Albizia julibrissin) 
12. English Oak (Quercus robur)
13. Coast live oak (Quercus agrifolia)
14. London plane (Platanus x acerifolia)
15. Cottonwood  (Populus fremontii)
16. Black cottonwood (Populus trichocarpa)
17. White Alder  (Alnus rhambifolia)
18. Titoki (Alectryon excelsus)
19. Engelmann Oak (Quercus engelmannii)
20. Cork Oak (Quercus suber)
21. Valley oak (Quercus lobata)
22. Coral tree (Erythrina corallodendon)
23. Blue palo verde (Cercidium floridum)
24. Palo verde (Parkinsonia aculeata)
25. Moreton Bay Chestnut  (Castanospermum australe)
26. Brea (Cercidium sonorae)
27. Mesquite (Prosopis articulata)
28. Weeping willow (Salix babylonica)
29. Chinese holly (Ilex cornuta) 
30. Camelia (Camellia semiserrata)
31. Acacia (Acacia spp.)
32. Liquidambar (Liquidambar styraciflua)
33. Red  Flowering Gum  (Eucalyptus ficifolia) 
34. Japanese wisteria (Wisteria floribunda)
35. Goodding's black willow (Salix gooddingii)
36. Tree of heaven (Alianthus altissima)
37. Kurrajong (Brachychiton populneus)
38. Black mission fig (Ficus carica)

 

Known Suitable Reproductive Host Trees of KSHB:

1. Avocado (Persea americana)
2. California Sycamore (Platanus racemosa) 
3. Big leaf maple (Acer macrophyllum)  
4. Coast live oak (Quercus agrifolia)
5. Cork oak (Quercus suber)
6. Coral tree (Erythrina humeana)

 

COMMENTS OF THE PEST AND DISEASE COMPLEX

Fusarium dieback (FD) is a new, invasive, beetle-vectored disease that has caused damage on avocado and other host trees in urban forests and wild lands in the Los Angeles basin since early 2012, and Orange and San Diego County since early 2013. This pest/disease complex has also impacted the avocado growing regions of Israel since 2009. DNA analyses of polyphagous shot hole borer (PSHB) beetles indicate that those from San Diego County are different from those in Los Angeles.and these beetles are now being called Kuroshio shot hole borer (KSHB) and are genetically similar to a beetle population in Taiwan. The beetles from Israel and the Los Angeles basin are genetically similar to those from Vietnam (Stouthamer unpublished data). Other studies have shown that species of Euwallacea, as well as thefusariumfungi they cultivate, are genetically distinct, including those from the Los Angeles basin (which are identical to those in Israel) and San Diego (O'Donnell 2014). These results indicate that at least two introductions into California have occurred. Each beetle carries its own novel pathogenic fungal species of Fusarium and Graphium, while the beetle from Los Angeles additionally carries a species of Acremonium (Lynch et al. in press).

Rapid spread of the beetle/fungi throughout various land use areas is attributed to the diverse range and quantity of suitable hosts in Southern California (Eskalen et al., 2013). Establishment of the beetle is a source of concern for the avocado industry, of which 90% of the United States crop is produced in California (California Avocado Commission). Several commercial avocado groves in Los Angeles County have been infested since 2012. The second invasion in San Diego County was not detected in commercial avocado groves until October 2014, one year after the initial finding on sycamore in El Cajon. Since then, 20 commercial avocado groves in San Diego County have been confirmed infested.

MANAGEMENT

Currently there are no control measures to control this pest. Early detection of infestation helps reduce the population of the beetle by removing infested branches where beetle can reproduce their offspring.

-If the infestation is on the branch collar, cut into branch collar and spray pruning wounds with a registered product of Bacillus subtilus.

-Chip infested wood on-site to a size of one inch or smaller. If the branch is too large to chip, solarize them under a clear tarp for several months

-Sterilize tools to prevent the spread of the disease with either 25% household bleach, Lysol^® cleaning solution, or 70% ethyl alcohol.

-Avoid movement of infested firewood and chipping material out of infested area.

-For more information visit http://eskalenlab.ucr.edu

 

The insect and the damage on avocado

PSHB damage

pshb insect

Polyphagous Shot Hole Borer: San Diego Population Now Known as Kuroshio Shot Hole Borer

Through DNA sequencing, UCR entomologist have determined that we have two separate invasions of the Polyphagous Shot Hole Borer (PSHB) here in southern California attacking avocados. One invasion in San Diego County and the second in Los Angeles County. UCR entomologist, Richard Stouthamer states the two are different species genetically, but morphologically they are indistinguishable, luckily they both respond to the same lure. They do however carry different fungal symbionts with them.

The species that has invaded San Diego, is now known as the Kuroshio shot hole borer, and is originally found only in two places in the presumed native range: highlands of Taiwan and in Okinawa. The species of beetle that has invaded Los Angeles County will now be known solely as the Polyphagous, its native range is in Vietnam, South China, North Thailand, low lands of Taiwan and Okinawa, this species has also invaded Israel and South Africa.

These Shot Hole Bores are Ambrosia beetles, a specialized group belonging to the family Scolytidae. The shot hole borer was first found in Whittier Narrows in Los Angeles County in 2003. From 2003-2010 the beetle was found on a few ornamental trees, then in 2010 it was the presumptive cause of the death of a large number of box elder street trees in Long Beach. In 2012 the beetle was collected from a backyard avocado tree in South Gate, and from several tree species at local botanical gardens, since then it has been causing havoc in the avocado industry. It now appears to be established in Los Angeles, Orange, San Bernardino and Riverside Counties, and is expanding its range in San Diego County. A single beetle was caught in Santa Cruz County in 2014 and has now been found less than 2 miles from Ventura County line.

 The beetle is dark brown to black and tiny, with females between 0.07 and 0.1 inches long, and males even smaller, usually about 0.05 inches long. They differ from the bark beetles in this family in several ways. While bark beetles burrow in the phloem layer or at the juncture of the bark and sapwood, ambrosia beetles bore through the bark and into the sapwood. The shot hole bores are highly specialized and feed on fungi that they cultivate on the walls of the tunnels. In the case of the shot hole bores, they transport the pathogenic fungus, Fusarium euwallacea and both the adults and larvae feed on the fungus.

Shot hole borers attacks hundreds of tree species, but it can only successfully lay its eggs and/or grow the fungi in certain hosts. These include: Avocado, Box elder, California sycamore, Coast live oak, White alder, Japanese maple, and Red willow. Visit http://eskalenlab.ucr.edu/ for the full list. Infection with the fungus can cause a dry or wet and oily dark stain surrounding the entry holes, discolored wood, leaf discoloration and wilting, and dieback of entire branches. In box elders and avocados, a while crusty ring of sugar, also called a “sugar volcano” can be produced. Frass (wood dust left behind from boring) may be produced, but because this can quickly dissolve if it rains it can be missed sometimes. If the barked is scraped away, dark dead tissue may be found around the galleries.

 

Currently there is no cure for the fungus once the tree has become infected. Chipping and solarizing/tarping infested wood can help to limit the spread of the beetle/fungus. Wood should be chipped to pieces smaller than 1". Don't forget to sterilize pruning tools between uses to avoid spreading the fungus.

 

If you suspect you may have the shot hole bore in your grove please feel free to contact your local CE Farm Advisor/Specialist.

Recent finding on Polyphagous Shot Hole Borer, Fusarium Dieback – A pest-disease complex on Avocado

The Polyphagous Shot Hole Borer (PSHB), Euwallacea sp. #1, is an invasive beetle that carries three fungi: Fusarium euwallaceae, Graphium sp. , and Acremonium sp. The adult female tunnels galleries into a wide variety of host trees, where it lays its eggs and grows the fungi. The fungi cause the Fusarium Dieback (FD) disease, which interrupts the transport of water and nutrients in over 35 tree species that are suitable for beetle reproduction.

Once the beetle/fungal complex has killed the host tree, pregnant females fly in search of a new host.

A separate invasion was recently detected in commercial avocado groves and landscape trees in San Diego county. It has been determined that the damage has been caused by another closely related species of PSHB (Euwallacea sp. #2), carrying a new species of Fusarium and Graphium. The beetle in LA, Orange, Riverside, and San Bernardino Counties are morphologically indistinguishable, but genetically distinct from the beetle found in San Diego County.

Signs and Symptoms

Attack symptoms, a host tree's visible response to stress, vary among host species. Staining, sugary exudate (B), gumming, and/or frass may be noticeable before the tiny beetles (females are typically 1.8-2.5 mm long). Beneath or near these symptoms, you may also see the beetle's entry/exit holes, which are ~0.85 mm in diameter. The abdomen of the female beetle can sometimes be seen sticking out of the hole.

Sugary exudate on trunks or branches may indicate a PSHB attack (photos A-E). Note that exudate may be washed off after rain events and therefore may not always be present on a

heavily infested branch. 

Hosts

PSHB attacks hundreds of tree species, but it can only successfully lay its eggs and/or grow the fungi in certain hosts. These include: Avocado, Box elder, California sycamore, Coast live oak, White alder, Japanese maple, and Red willow. Visit eskalenlab.ucr.edu for the full list.

Fusarium dieback pathogens cause brown to black discoloration in infected wood. Scraping away bark over the entry/exit hole reveals dark staining around the gallery, and cross sections of cut branches show the extent of infection. Advanced infections eventually lead to branch dieback and death of the tree 

How to report a suspect tree

Please report suspected tree infestations to UC Riverside (eskalenlab@gmail.com).

Submit the following information:

•Contact information (name, city, phone number, email)

•Suspect tree species

•Description of suspect tree's location (and/or GPS coordinates)

•Description of suspect tree's symptoms

•Photos of suspect tree and close-up photos of symptoms (see examples)

Take photos of suspect trees from several distances. Include photos of:

1. the trunk or symptomatic branches;

2. the symptoms (close-up); and

3. the entry/exit hole, if visible, with a ballpoint pen for scale (remove exudate if necessary). If dieback is observed, take a picture of the entire tree.

 

shothole 1

shothole 2

shothole 3

shothole 4

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