Agrilus biguttatus

 
IDENTITY
Name:   Agrilus biguttatus
Pest Authorities:  (Fabricius)
Taxonomic Position:  Insecta: Coleoptera: Buprestidae
Sub-specific Taxon:  
Pest Type:   Insect
Common Name(s):
   Oak splendour beetle (English)
   Pilkkujalosoukko (Finnish)
   Two-Spotted wood-borer (English)
   Zweipunktiger Eichenprachtkäfer (German)
Synonym(s):
   Agrilus pannonicus (Pillar and Mittlerpache)
 
RISK RATING SUMMARY
Numerical Score:  9
Relative Risk Rating:  Very High Risk
Uncertainty:   Very Uncertain
Uncertainty in this assessment results from: The ability of this insect to compete successfully with indigenous woodborers of oaks, especially the two-lined chestnut borer, Agrilus bilineatus, is not known.

RISK RATING DETAILS
Establishment Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Suitable climatic conditions and suitable host material coincide with ports of entry or major destinations.
  • Organism has active, directed host searching capability or is vectored by an organism with directed, host searching capability.
  • Organism has high inoculum potential or high likelihood of reproducing after entry.
Justification: Climatic conditions and suitable hosts for Agrilus biguttatus occur at many North American ports of entry. This insect has a directed host searching capability and would have a high likelihood of reproducing after entry, provided that it can compete successfully with North American oak borers such as A. bilineatus. A related species, the emerald ash borer, A. planipennis, native to Asia, has recently become established in North America.

Spread Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism is capable of dispersing more than several km per year through its own movement or by abiotic factors (such as wind, water or vectors).
  • Potential hosts have contiguous distribution.
  • Newly established populations may go undetected for many years due to cryptic nature, concealed activity, slow development of damage symptoms, or misdiagnosis.
  • Eradication techniques are unknown, infeasible, or expected to be ineffective.
  • Organism has broad host range.
Justification: Adults are relatively strong fliers, capable of flying several km in search of suitable hosts. This insect could also be spread via unprocessed oak logs or wood products containing strips of bark. Oaks, the primary host of Agrilus biguttatus are widely distributed in North America, especially in the eastern portions of the continent and have contiguous distributions. Newly established populations could go undetected for a number of years because of the insect’s cryptic nature and the fact that the genus Agrilus is well represented in North America.

Economic Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism attacks hosts or products with significant commercial value (such as for timber, pulp, or wood products.
  • Organism directly causes tree mortality or predisposes host to mortality by other organisms.
  • Organism may cause loss of markets (domestic or foreign) due to presence and quarantine significant status.
  • No effective control measure exists.
Justification: Oaks, the primary host of Agrilus biguttatus, are important trees for lumber, flooring and cooperage. They are also popular ornamental trees in urban settings. This insect is potentially capable of causing severe damage to oak forests. Moreover, quarantine measures designed to slow the rate of spread of this could have an adverse affect on the movement of oak logs, nursery stock and firewood. Eradication and control of this insect would be extremely difficult because of its cryptic nature and similarity in appearance to indigenous species.

Environmental Potential Is High Risk
The relevant criteria chosen for this organism are:  
  • Organism is expected to cause significant direct environmental effects, such as extensive ecological disruption or large scale reduction of biodiversity.
  • Introduction of the organism would likely result in control/eradication programs that may have potential adverse environmental affects.
Justification: This insect has the potential to cause extensive tree mortality in North American oak forests, especially forests defoliated by gypsy moth, Lymantria dispar, other defoliating insects or stressed by drought. This could alter the composition of many eastern oak-hickory forests in favor of non-host species.

 
HOSTS
The primary hosts of Agrilus biguttatus are oaks, Quercus spp., including Quercus robur, Quercus petraea, Quercus pubescens, Quercus ilex, Quercus suber and Quercus cerris. Infestations are found occassionally in European beech, Fagus sylvatica and chestnut, Castanea sativa. Several records exist of this insect attacking poplars, Populus spp. These are considered doubtful, however. Infestations in the North American red oak, Quercus rubra, planted within the geographic range of A. biguttatus, are rare (Moraal and Hilszanski 2000).

 
GEOGRAPHICAL DISTRIBUTION
Africa:
     Northern Africa (presumably Algeria, Morocco and Tunisia) (Moraal and Hilzczanski 2000).
Asia:
     Near East, Siberia (Moraal and Hilszczanski 2000).
Europe:
      Agrilus biguttatus is found throughout Europe except Finland (Azerbaijan, Belarus, Czech Republic, England, France, Germany, Hungary, the Netherlands, Poland, Russia, Ukraine) (Moraal and Hilszczanski 2000).
 
BIOLOGY
The genus Agrilus is a large genus of flatheaded woodborers with species found in Asia, Australia, Europe and North America (Browne 1968). The larvae typically feed in the cambium of trees or in the stems of small woody plants. The adults are colorful insects with striking metallic colors and are often referred to as jewel beetles. Several species are of economic importance in forestry, arborculture and agriculture. About 100 species are native to North America including A. angelicus, a pest of ornamental oaks in California (Furniss and Carolin 1977) and the bronze birch borer, A. anxius, a pest of birches and a contributing factor to birch dieback, a condition which occurred over eastern Canada and the northeastern U.S. between 1930 and 1950 (Ciesla and Donaubauer 1994). The two-lined chestnut borer, A. bilineatus , attacks oaks in eastern North America (Drooz 1985, Haack and Acciavatti 1992) and is a contributing factor to North American oak decline (Ciesla and Donaubauer 1994). A. bilineatus and A. biguttatus are probably ecological counterparts. A. hyperici bores in the roots of St. John’s wort, Hypericum peforatum, an invasive weed, and has been introduced into portions of the western U.S. as a biological control agent (Krueger and Sheley 2002).

Agrilus biguttatus may have one generation a year but a two-year cycle is more common. In northern Germany, the larvae hibernate over two winters. Adult flight occurs from May to July. After maturation feeding on foliage in the crowns of oaks, females deposits clusters of 5-6 eggs in bark crevasses. The south facing side of large oaks (DBH of 30-40 cm) is preferred for oviposition.

Larvae feed in the cambium layer in longitudinal, winding, “zig-zag” galleries and overwinter in side the bark. They undergo five instars. When feeding is completed, an individual larva may excavate a gallery up to 155 cm long. The pupae develop in the bark, in chambers 10.4-14.4 mm long and 3.0-4.5 mm wide. Adults remain under the bark for about two weeks in late spring-early summer and construct D-shaped exit holes through which they emerge (Moraal and Hilczczanski 2000) .

Several species of natural enemies of Agrilus biguttatus have been reoprted. Woodpeckers feed on the overwintering larvae. Parasitoids include Spathius curvicaudus, a gregarious species, S. ligiarus, S. radzayanus and Atanycolus neesi (Hymenoptera: Braconidae) (Moraal and Hilczczanski 2000).

Typically infestations are progressive and require two to three years to kill a tree. In heavily infested trees, the entire mainstem contains galleries and the trees are girdled and killed in a single season.

 
PEST SIGNIFICANCE
Economic Impact:    Young larvae construct longitudinal galleries. Older larvae produce galleries in irregular, twisting, transverse directions. This can lead to partial or complete girdling of trees. Larval activity can result in twig and branch dieback, thin crowns and epicormic branching. Heavily infested trees or trees attacked for several successive years will die (Moraal and Hilszczanski 2000).

In its native range, Agrilus biguttatus, has been regarded as a secondary invader of stressed and weakened trees. It is frequently found in trees that have been stressed by insect defoliation, frost damage or warm, dry summers (Anon 2002, Hiller 1998). This insect has recently been associated with a European oak decline throughout its natural range, as a contributing factor (Gibbs and Grieg 1997, Hartman and Blank 1992, Rohde 1999). Infestations can result in extensive tree mortality.

Recently, attacks by Agrilus biguttatus have increased in several European countries including England, France, Germany, Hungary, Poland and the Netherlands (Moraal and Hilszczanski 2000). In England, for example, this species was regarded as endangered as recently as 1987 but is now a common tree killer in oak woodlands and parks (Gibbs and Grieg 1997).

Environmental Impact:   Extensive mortality of oak forests due to a complex of factors including Agrilus biguttatus, known as oak decline, can alter the species composition of forests. As a secondary insect, A. bigutattus is one of a large group of insects instrumental in the decomposition of dead trees

Control:    Direct control of this insect has not been considered practical. Pest management involves maintenance of healthy oak forests through forest management including thinning of oak forests and timely harvesting of mature trees (Anon 2002, Hiller 1998). Similar pest management recommendations are in place for the indigenous two-lined chestnut borer (Haack and Acciatvatti 1992). With the recent increase in tree mortality attributed to this insect, removal of infested stems has been suggested as a possible means to reduce losses (Moraal and Hilszczanski 2000).

 
DETECTION AND IDENTIFICATION
Symptoms:    Symptoms of attack include dieback, development of epicormic branches, thin crown, tree mortality, frass-filled transverse, winding larval galleries in the cambium layer, D-shaped adult exit holes and the presence of insect life stages (Moraal and Hilszczanski 2000).

Morphology:    Adults are attractive, slender, subcylindrical insects, 9-12 mm long. They are metallic green in color. The posterior third of the elytra have two distinct white marks on their interior edge.

The mature larvae are legless grubs, 25-43 mm long when mature and creamy white in color. The first thoracic segment is wider than the other body segments. Two hornlike projections are found on the last abdominal segment (Anon 2002, Moraal and Hilszczanski, 2000).

Testing Methods for Identification:    Examination of adults by a taxonomist with expertise in the family Buprestidae is required for positive identification.

 
MEANS OF MOVEMENT AND DISPERSAL
Adults are strong fliers on warm, sunny days and could travel several km. in search of suitable host material. This insect could be transported in wood products moving via international trade. To date, at least six exotic species of Agrilus have become established in the U.S. Between 1985 and 2000, 38 confirmed interceptions of Agrilus spp. were made at U.S. ports of entry. Twenty-eight of these interceptions were from dunnage, 4 from crating, 4 from grape leaves, 1 from a cutting and one was at large in a ship’s hold. A related species, the emerald ash borer, Agrilus planipennis, has recently become established in southern Michigan, U.S. and neighboring portions of Canada, where it has become a serious pest of ash trees in both urban and forest ecosystems (Haack et al. 2002).

 
BIBLIOGRAPHY
Anonymous 2002 . Agrilus biguttatus, Zweipunktiger Eichenprachtkäfer (Coleoptera Buprestidae). On line: http://faunistik.net/detinvert/coleoptera/buprestidae/agrilus/agri, 3 pp. (In German)
Browne, F.G. 1968. Pest and diseases of forest plantation trees. Oxford: Clarendon Press, 1330 pp.
Ciesla, W.M.; Donaubauer, E. 1994 . Decline and dieback of trees and forests: A global overview. Rome, Italy: Food and Agriculture Organization of the United Nations, Forestry Paper 120, 90 pp.
Drooz, A.T., 1985. Insects of eastern forests. USDA Forest Service, Miscellaneous Publication 1426, 608 pp.
Furniss, R.L.; Carolin, V.M. 1977. Western forest insects. USDA Forest Service, Miscellaneous Publication 273, 654 pp.
Gibbs, J.N.; Grieg, B.J.W. 1997. Biotic and abiotic factors affecting the dying back of penunculate oak, Quercus robur L. Forestry 70 (4): 399-406.
Haack, R. A.; Jendek, E.; Houping Liu; Marchant, K.R.; Petrice, T.R; Poland, T.M.; Hui Ye 2002. The emerald ash borer: A new exotic pest in North America. Newsletter of the Michigan Entomological Society 47 (3-4): 1-5
Haack, R.A.; Acciavatti, R.E. 1992. Twolined chestnut borer. USDA Forest Service, Forest Insect and Disease Leaflet 168, 10 pp.
Hartmann G.; Blank, R. 1992. Winterfrost, Kahlfrass und Prachtkäferbefall als Faktoren im Uraschencomplex des Eichensterbens in Norddeutschland. Forst und Holz 47: 443-452 (In German)
Hiller. E. 1998. Schäden und biologie des Eichenprachtkäfers. On line: http://www:lwf.bayern.de/veroef/veroef98/lwfakt15/lwfak15f.htm (In German).
Krueger, J.; Sheley, R. 2002. St Johnswort (Hypericum perforatum). Montana State University, Extension Service, MT 199810AG, 4 pp.
Moraal, L.G.; Hilszczanski, J. 2000. The oak buprestid beetle, Agrilus biguttaus (F.) (Col., Buprestidae), a recent factor in oak decline in Europe. Anz. Schädlingskunde/ Journal of Pest Science 73: 134-138
 
AUTHOR(s)
Name(s):
William M. Ciesla
 
 
Name and Address of the First Author:
William M. Ciesla
Forest Health Management International
2248 Shawnee Court
Fort Collins, CO
USA 80525
 
CREATION DATE:        06/23/03
MODIFICATION DATE:        06/23/03

    
Selected images from Forestry Images (www.forestryimages.org)
View all images

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1231055

Adult(s)
Photo by Gyorgy Csoka,
Hungary Forest Research Institute

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2515032

Larva(e)
larva (final stage)
Photo by Louis-Michel Nageleisen,
Département de la Santé des Forêts - France


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2515037

Pupa(e)
in the bark
Photo by Louis-Michel Nageleisen,
Département de la Santé des Forêts - France

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2515039

Galleries
in the shape of stairs (first stage)
Photo by Louis-Michel Nageleisen,
Département de la Santé des Forêts - France


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2515035

Galleries
gallery in shape of zig-zag (final stage) and cambium necrosis
Photo by Louis-Michel Nageleisen,
Département de la Santé des Forêts - France

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2515036

Damage
dead tree infested by agrilus
Photo by Louis-Michel Nageleisen,
Département de la Santé des Forêts - France