Agelastica alni alni

 
IDENTITY
Name:   Agelastica alni alni
Pest Authorities:  Linneaus
Taxonomic Position:  Insecta: Coleoptera: Chrysomelidae
Sub-specific Taxon:  alni
Pest Type:   Insect
Common Name(s):
   Alder leaf beetle (English)
   Blauer Erlenblattkäfer (German)
   Galéruque de l’aulne (French)
   Idänlehtikouriainen (Finnish)
   La chrysomèle de l’aulne (French)
Synonym(s):
 
RISK RATING SUMMARY
Numerical Score:  4
Relative Risk Rating:  Moderate Risk
Uncertainty:   Very Uncertain
Uncertainty in this assessment results from: The ability of Agelastica alni to compete with indigenous Chrysomelidae or other broadleaf defoliators is not known.

RISK RATING DETAILS
Establishment Potential Is Moderate 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 high inoculum potential or high likelihood of reproducing after entry.
Justification: Suitable climatic conditions and host material (alder) coincide with many ports of entry in North America, especially in the more northerly locations. This insect has a high reproductive rate and is capable of multiplying into large numbers capable of causing severe defoliation to host plants in its native habitat.

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).
  • Organism has a high reproductive potential
  • 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: Agelastica alni adults are capable of short distance flights and can spread slowly through areas of suitable host type. This insect could be moved via international trade in plant materials such as nursery stock but the eggs, larvae and adults are fairly conspicuous and should be easily detected. It has a high reproductive potential and species of alder, the favorite host, are relatively abundant, especially in riparian areas in North America. Since this insect resembles the native alder flea beetle, Altica ambiens, established infestations might be difficult to detect and eradication would also be difficult. While this insect prefers alder, it is capable of feeding on a variety of broadleaf species.

Economic Potential Is Moderate 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.
Justification: Mortality of young trees and growth loss of older trees would be expected if Agelastica alni were to become established. Over most of North America, the primary damage would be defoliation of trees in parks, residential areas and forest recreation sites. Economic damage could occur in the Pacific Northwest, where red alder, Alnus rubra, is an important species for high quality veneer and cabinetry.

Environmental Potential Is Moderate Risk
The relevant criteria chosen for this organism are:  
  • Introduction of the organism would likely result in control/eradication programs that may have potential adverse environmental affects.
Justification: Since extensive mortality of mature trees is not expected to occur, ecological damage is expected to be minor. However, direct control of unsightly infestations in parks, residential areas and recreation sites with chemical or biological insecticides, if needed, could have a number of undesirable side effects.

 
HOSTS
The favorite host plants of Agelastica alni are various species of alder, Alnus spp. Other hosts include poplars, Populus spp., willows, Salix spp. and hazelnut, Corylus spp. (www.insektenbox.de/kaefer/erlebl.htm, (www.faunistik.net/DETINVERT/COLEOPTERA/CHRYSOMELIDAE/AGELAS, Zhuravlev and Osmolovskii 1964).

 
GEOGRAPHICAL DISTRIBUTION
Europe:
     This insect is widely distributed across Europe from the British Isles and France east to western Russia (Fennoscandia, Murmansk, Karelia and St. Petersburg) and north to Finland.
 
BIOLOGY
Agelastica alni has one generation a year. Both the larvae and adults feed on the foliage of host plants. This genus is not represented in North America. However, a related species, the alder flea beetle, Altica ambiens (Coleoptera: Chrysomelidae), has a transcontinental distribution in North America and causes damage similar to that caused by A. alni (Furniss and Carolin 1977).

Adults overwinter in the litter, become active in May, when they feed on foliage and mate. Females lay eggs in groups of 60-70 on the undersides of the foliage of host plants.

Larvae hatch after 5-14 days and feed on the epidermal tissue on the undersides of foliage. Duration of the larval stage is about three weeks, during which they pass through three instars. Mature larvae are capable of skeletonizing the foliage.

Pupation takes place in oval chambers in the soil under the litter during July and August. The duration of the pupal stage is about 10 days. Adults emerge and feed on foliage during August (www.insektenbox.de/kaefer/erlebl.htm, (www.faunistik.net/DETINVERT/COLEOPTERA/CHRYSOMELIDAE/AGELAS,)

The larvae of Agelastica alni discharge a fluid from openings located dorso- ventrally on paired tubercles of the first to eighth abdominal segments when disturbed. These are a chemical defense system that causes them to be avoided by many generalist predators (Baur and Rank 1996, Bünige and Hilker 1999).

 
PEST SIGNIFICANCE
Economic Impact:    Agelastica alni is capable of multiplying to great numbers and can devour almost all of the foliage of alder trees and shrubs. Affected plants appear from a distance as though they have been scorched by fire (Zhuravlev and Osmolovskii 1964). Resultant damage is unsightly and repeated heavy defoliation can cause growth loss in large trees and mortality of young plants. This insect can be a pest of ornamental trees in parks and residential areas but is not considered a major forest pest (www.faunistik.net/DETINVERT/COLEOPTERA/CHRYSOMELIDAE /AGELAS)

Environmental Impact:   Foliar injury can be unsightly in residential areas, parks and forest recreation sites. Overall ecological impact is not significant, however.

Control:    Infestations in parks and residential areas can be treated with insecticide applications. Direct control is not undertaken in forested areas.

 
DETECTION AND IDENTIFICATION
Symptoms:    The primary symptom is defoliation of alder. Heavy defoliation will give trees a scorched appearance. Examination of foliage during the growing season should reveal presence of eggs, larvae or adults.

Morphology:    Eggs are ovoid to cylindrical in shape and yellow ochre in color. Dimensions are ca 0.9x0.5 mm.

First instar larvae are olive green in color and later darken to a shiny blue-green to black color. Mature larvae are about 12 mm in length.

The adults are 6-7 mm in length, shiny, and blue black in color with greenish or violet highlights. The antennae are black and filiform and approximately half the body length. The elytra are wider in the posterior portion and contain dense, fine punctures (www.insektenbox.de/kaefer/erlebl.htm).

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

 
MEANS OF MOVEMENT AND DISPERSAL
Adults are capable of flying short distances and can spread slowly. Eggs, larvae and adults could be transported as hitchhikers on plant materials via international trade. However, they are fairly conspicuous and should be easily detected.

 
BIBLIOGRAPHY
Baur, R.; Rank, N.E. 1996. Influence of host quality and natural enemies on the life history of the alder leaf beetles, Agelastica alni and Linaedea aenea. In: Chrysomelidae Biology, V.2. Ecological Studies, Amsterdam: SPB Publishing, pp 173-194.
Bünnige, M; Hilker, M. 1999. Larval exocrine glands in the galerucine Agelastica alni L. (Coleoptera: Chrysomelidae): their morphology and possible functions. Chemoecology 9:55-62
Furniss, R.L.; Carolin, V.M. 1977. Western forest insects. USDA Forest Service, Miscellaneous Publication 273, 654 pp.
Zhuravlev, I.I.; Osomolovskii, G.E. 1964.. The principal pests and diseases of shade trees. Jerusalem, Israel: Israel Program for Scientific Translations, 185 pp. (Translated from the original Russian published in 1949).
 
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:        05/17/03
MODIFICATION DATE:        05/17/03