Eulachnus rileyi
(pine needle aphid)

Pictures

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Identity

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Preferred Scientific Name

• Eulachnus rileyi (Williams)

Preferred Common Name

• pine needle aphid

Other Scientific Names

• Lachnus rileyi Williams

Local Common Names

• Italy: afido del pino

EPPO code

• EULARI (Eulachnus rileyi)

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Arthropoda
•             Subphylum: Uniramia
•                 Class: Insecta
•                     Order: Hemiptera
•                         Suborder: Sternorrhyncha
•                             Unknown: Aphidoidea
•                                 Family: Aphididae
•                                     Genus: Eulachnus
•                                         Species: Eulachnus rileyi

Notes on Taxonomy and Nomenclature

Top of page This aphid was originally described as Lachnus rileyi by Williams in 1910 and later placed in the genus Eulachnus. This species is closely related to Eulachnus agilis. Forms with apparently intermediate or combined characters of the two species occur in southern and Central Europe. Several subspecies and intermediate species have been described. However, without further biological information, Blackman and Eastop (1994) suggested that these forms were best regarded as geographic or environmentally determined variants of E. rileyi.

Description

Top of page All life stages of E. rileyi are olive-brown and powdery. Detailed descriptions of the life stages, as described by Palmer (1952), are given in the following sections.
Apterous Vivipara

The wingless parthenogenetic form has black legs and a dark body. It is 2 to 2.6 mm long and 0.6 mm wide. The cornicle consists of a ring without a conical base. The cauda is usually rounded but with an upturned tip, which, when extended, appears pointed.

Alate Vivipara

This form is the same size and colour as the apterous vivipara. The secondary sensoria are absent on segment three and there is one on segment four. The hairs are heavy, 0.1 mm long, spike-like on the vertex, sparse and inconspicuous on the body, and moderately numerous on the appendages. The lengths of the hairs on the hind tibia are at least twice the diameter of the tibia. The rostrum is broad and obtuse. The forewing has a faint media that is usually forked once.

Apterous Ovipara

The apterous ovipara is similar in appearance to the apterous vivipara except that the hind tibia is 1.3 to 1.65 mm long with the proximal half moderately swollen and rather thickly covered with flat sensoria.

Alate Male

This stage is similar in appearance to the alate vivipara except for the antennae, which are much longer (approximately 1.75 mm). In addition, the sensoria are numerous on segments three and four.

Distribution

Top of page Blackman and Eastop (1994) reported the distribution of E. rileyi as "Europe, Mediterranean area, southwest Asia and introduced into Africa, south of the equator, North, South and Central America".

The distribution map includes records based on specimens of E. rileyi from the collection in the Natural History Museum (London, UK): dates of collection are noted in the List of countries (NHM, various dates).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Risk of Introduction

Top of page The recent introduction and establishment of E. rileyi in Africa and South America, and its historic establishment in North America, suggest that this insect can be easily moved via human actions. Moreover, Eulachnus thunbergerii, native to Asia, has become established in Australia (CSIRO, 2002) and a European species, Eulachnus brevipilosus, has become established in New Zealand (Zondag, 1983).

Habitat

Top of page E. rileyi occurs in natural pine forests and plantations. It is reported as rare to uncommon over its native geographic range (Europe). It has been introduced into Africa and North America.

Hosts/Species Affected

Top of page E. rileyi feeds on the needles of many pine species. In places where it has been introduced, it has readily adapted to indigenous or introduced species. In Europe, it is more commonly found on Pinus nigra (black pine) and Pinus mugo (mountain pine) than on Pinus sylvestris (Scots pine) (Blackman and Eastop, 1994).

Host Plants and Other Plants Affected

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Growth Stages

Top of page Vegetative growing stage

Symptoms

Top of page Feeding by E. rileyi causes a characteristic mottling and yellowing of the crowns of infested trees. Other symptoms of infestation include the presence of insect life stages, copious amounts of honeydew, the presence of black sooty mould, which forms on the needles and branches, and the presence of ants of the genus Camponotus, which tend the aphid colonies.

List of Symptoms/Signs

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Biology and Ecology

Top of page Life History and Habits

The genus, Eulachnus, consists of approximately 20 species distributed across the Holarctic conifer forests. They have sucking mouthparts and feed on the sap of host trees. Some species only feed on the needles and others (e.g. Eulachnus brevipilosus) suck the sap from twigs, shoots and needles. Like many aphids, the life history and habits of members of the genus Eulachnus are complex and there are a number of life stages. In addition, the life cycle and occurrence of certain life forms is determined by local climatic conditions.

In northern temperate climates, E. rileyi exhibits heterogamy or cyclic reproduction. This consists of an alternation of asexual and sexual generations. The egg stage is the overwintering stage. The eggs hatch in the spring to produce a fundatrix or stem mother. The stem mothers reproduce parthenogenetically and viviparously (bringing forth live young). Generations subsequent to the fundatrix are known as the summer viviparae. They consist of apterous (wingless) and alate (winged) viviparous summer females known as viviparae. The summer viviparae reproduce in the same manner as the fundatrices for several generations during the summer. The sexuales typically appear at the end of the summer and consist of a true apterous female and males that can be either apterous or alate. This final generation of females is oviparous and lays eggs, which remain dormant until the following spring. Observations in the Rocky Mountain region of the USA indicate that apterous and alate viviparae are present from 20 June to 5 September and sexuales are present from 24 September to 7 October (Palmer, 1952).

Studies on the biology of E. rileyi in Africa, where this insect has been introduced and established, indicate that this species has a reduced life cycle and reproduces throughout the year without the sexual forms. All stages (nymphs and adults) feed on the undersides of pine needles of trees of all ages. The females are normally apterous, although alatae are sometimes produced (Murphy et al., 1991).

In Africa, the abundance of E. rileyi is regulated to some degree by the cycle of alternating dry and rainy seasons. In Zambia, in 1978 and 1979, the build-up of pine needle aphid populations was rapid in May to June after the rains had ceased, and the onset of the rains caused a drastic decrease in the population density from November to December (Loyttyniemi, 1979). In Iraq, populations of E. rileyi seem to be adversely affected by hot, dry weather. In a life history study, Abdullah and Mohammad (1991) reported that in Iraq, small numbers of E. rileyi were first seen at the end of March. Numbers peaked during the fourth week of April and disappeared during the third week of June, with the onset of hot summer weather.

E. rileyi feeds on mature or senescing needles throughout the crowns of host trees (Chilima, 1991). Infestations cause needles of host pines to turn yellow and the aphids produce copious amounts of honeydew. The honeydew provides a medium for the development of sooty moulds on heavily infested trees (Murphy et al., 1991).

Natural enemies

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Notes on Natural Enemies

Top of page In Zimbabwe, eight species of insect predators of E. rileyi have been identified. Coccinellids and Syrphidae larvae are the most important. The fungus Entomophthora planchoniana maintained effective control of the aphid in two separate areas. The fungus Stilbella burmensis infects ants of the genus, Camponotus, which tend colonies of E. rileyi. This fungus has a beneficial effect because the aphid colonies have less protection from predators due to the fewer numbers of ants (Katerere, 1984). At least two species of parasitoids are known to attack E. rileyi.

The parasitoid, Diaeretus leucopterus, has been studied as a potential classical biological control agent for both Eulachnus agilis and E. rileyi. Levels of parasitism by D. leucopterus are consistently low and the insect is subjected to high levels of hyperparasitism. These studies suggest that this parasitoid is not an effective biological control agent unless it is used in combination with other complementary natural enemies (Murphy and Völkl, 1996).

Means of Movement and Dispersal

Top of page The natural dispersal of aphids, including E. rileyi, is via the winged life stages and air currents. However, these dispersal mechanisms are inefficient because the probability of an aphid locating a suitable host plant is low, resulting in high rates of mortality. If a single summer viviparous parthenogenetic female succeeded in landing on a suitable host, she could establish a new population without mating.

The most likely pathway for movement of these aphids around the world is via infested pine nursery stock in international trade. The nymphs and adults on leaves are visible to the naked eye but the eggs are not.

Plant Trade

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Plant parts not known to carry the pest in trade/transport
Bark
Flowers/Inflorescences/Cones/Calyx
Fruits (inc. pods)
Growing medium accompanying plants
Roots
Seedlings/Micropropagated plants
Stems (above ground)/Shoots/Trunks/Branches
True seeds (inc. grain)
Wood

Wood Packaging

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Impact

Top of page E. rileyi is relatively uncommon within its native geographic range and is not considered to be a pest. In areas where it has been introduced, it has caused varying degrees of damage. For example, in Venezuela, Rosales and Cermeli (1995) reported that E. rileyi poses a threat to 500,000 ha of pine plantations. During the dry season, moderate to severe damage has been observed in the small plots of pine that have been designated for seed production but not in the large commercial plantations. In eastern and southern Africa, E. rileyi is considered to be the least damaging of three conifer aphids that have been introduced into the region; the other two are Cinara cupressivora [Cinara cupressi] and Pineus borneri. However, since their introduction and establishment in eastern and southern Africa, E. rileyi and P. borneri have collectively caused a loss of approximately £1.5 million per year to the annual growth increment in pine plantations (Murphy, 1996).

This aphid has recently been implicated as a vector of mycoplasma-like organisms (MLOs) that cause yellows diseases of pines. In a study in Zimbabwe, both light and electron microscopic examinations showed tissue colonization with MLOs when the salivary glands and mid-gut tissues from E. rileyi, which were actively feeding on infected pines, were examined (Gopo et al., 2002).

Environmental Impact

Top of page Since this insect is relatively uncommon within its native geographic range, and causes little or no damage to its hosts, there are no known adverse environmental impacts. In places where E. rileyi has been introduced (Africa, South America), host pines are also introduced. Therefore, there are no environmental impacts on the indigenous ecosystems.

Detection and Inspection

Top of page Pines should be inspected for yellow mottling or necrotic needles and insect life stages.

Similarities to Other Species/Conditions

Top of page E. rileyi is similar in overall appearance to Eulachnus agilis, which also has an Holarctic distribution. However, E. agilis has a green body and E. rileyi has a brown body, with slightly larger antennae and hind tibiae.

Prevention and Control

Top of page Since E. rileyi is relatively uncommon within its native geographic range and causes little or no damage, control has not been necessary. Varying degrees of damage have been reported in areas where it has been introduced. However, the development of pest management tactics has, thus far, been limited to classical biological control.
Biological Control

Classical biological control programmes for E. rileyi could be developed in areas where this insect has become established and is causing severe damage to pine plantations. However, in eastern and southern Africa, where E. rileyi was one of three conifer aphids included in such a programme, it received a low priority because it was the least damaging of the three. The braconid parasitoid, Diaeretus leucopterus, has been studied as a potential biological control agent for Eulachnus sp. (Murphy and Völkl, 1996).

Field Monitoring

Field monitoring for the detection of infestations involves the examination of pine forests for the presence of damage and insect life stages. In Venezuela, the life stages of E. rileyi have been captured on impact- and intercept-traps but not in yellow water traps (Rosales and Cermeli, 1995).

Integrated Pest Management

The integrated pest management (IPM) of E. rileyi is presently limited to monitoring for the insect in areas where it has become established and the development of classical biological control programmes.

References

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Abdullah IN; Mohammad MA, 1991. Seasonal abundance and population density of pine aphid, Eulachnus rileyi W. (Homoptera, Aphididae) in Hammam Al-Alil region. Arab Journal of Plant Protection, 9(1):19-22

Blackman RL; Eastop VF, 1994. Aphids on the world's trees: an identification and information guide. Wallingford, UK: CAB International.

Chilima CZ, 1991. The status and development of conifer aphid damage in Malawi. Workshop Proceedings. Exotic aphid pests of conifers: a crisis in African forestry, Muguga, Kenya: Kenya Forest Research Institute and Food and Agriculture Organization of the United Nations, 64-67.

CSIRO, 2002. 2. Scientific names: Eulachnus thunbergii Wilson. CSIRO Australia & AFFA. http://www.ento.csiro.au/aicn/name_s/b_1282.htm.

Delfino MA; Eastop VF, 1980. Contribution to the knowledge of the pine aphids (Homoptera, Aphidoidea: Lachnidae) in Argentina. Revista de la Sociedad Entomologica Argentina, 39(3/4):143-148

Fuentes-Contreras E; Muñoz R; Niemeyer HH, 1997. Diversidad de Aphidoidea en Chile (Hemiptera: Aphidoidea) (Diversity of Aphidoidea in Chile). Revista Chilena de Historia Natural, 70:531-542.

Gopo JM; Mutika G; Wessels DCJ, 2002. Mycoplasma-like-organisms (MLOs): as causal agents for the yellow type of plant disease in pine and cyprus trees in Zimbabwe. Discovery and Innovation, No.Special Edition:106-114; 7 ref.

Halperin J, 1986. Eulachnus rileyi - a new pine aphid in Israel. Phytoparasitica, 14(4):319

Jaskiewicz B; Sawinska A, 2005. Aphids (Homoptera, Aphidodea) inhabiting the shrubs of Pinus mugo Turra in the green areas of Lublin. Part I. The population dynamics. Acta Agrobotanica, 58(1):153-164.

Katerere Y, 1983. The fungus Entomophthora planchoniana Cornu (non Thaxter). The pine needle aphid Eulachnus rileyi (Williams) Zimbabwe. Commonwealth Forestry Review, 62(4):271-273

Katerere Y, 1984. Biology and population dynamics of the pine needle aphid, Eulachnus rileyi (Williams) in Zimbabwe. South African Forestry Journal, No. 129:40-49

Kiwuso P, 1995. The current conifer aphid situation in Uganda. In: Proceedings, Biological control of conifer aphids in Africa, Country updates and progress reports, 1991-1993, Muguga, Kenya, 6 December 1993. International Institute of Biological Control, Kenya Station, CABI, 61-62.

Loyttyniemi K, 1979. Eulachnus rileyi (Williams) (Homoptera, Lachnidae) infesting pines in Zambia. Annales Entomologici Fennici, 45(4):116

Massawe A; Kisaka EZ, 1995. Current status of conifer aphids in Tanzania. In: International Institute of Biological Control, eds. Proceedings of biological control of conifer aphids in Africa, Country updates and progress reports, 1991-1993, Kenya Station CABI, Muguga, Kenya: International Institute of Biological Control, 55-59.

Murphy ST, 1996. Status and impact of invasive conifer aphid pests in Africa. Impact of diseases and insect pests in tropical forests. Proceedings of the IUFRO Symposium, Peechi, India, 23-26 November 1993., 289-297; 16 ref.

Murphy ST; Abraham YJ; Cross AE, 1991. Ecology and economic importance of the aphid pests, Pineus sp. and Eulachnus rileyi on exotic pine plantations in southern and eastern Africa. In: Ciesla WM, Odera J, Cock MJW, eds. Workshop Proceedings, Exotic aphid pests of conifers: A crisis in African forestry. Mugaga, Kenya: Kenya Forest Research Institute and Food and Agriculture Organization of the United Nations, 48-53.

Murphy ST; Völkl W, 1996. Population dynamics and foraging behaviour of Diaeretus leucopterus (Hymenoptera: Braconidae), and its potential for the biological control of pine damaging Eulachnus spp. (Homoptera: Aphididae). Bulletin of Entomological Research, 86(4):397-405; 50 ref.

Owour AL, 1991. Exotic conifer aphids in Kenya, their current status and options for management. In: Ciesla WM, Odera J, Cock MJW, eds. Workshop Proceedings, Exotic aphid pests of conifers: A crisis in African forestry. Mugaga, Kenya: Kenya Forest Research Institute and Food and Agriculture Organization of the United Nations, 58-63.

Palmer MA, 1952. Aphids of the Rocky Mountain Region. Colorado, USA: The Thomas Say Foundation.

Rosales CJ; Cermeli M, 1995. Observations on the aphid Eulachnus rileyi Williams (Homoptera: Aphididae) on Pinus caribaea var. hondurensis Barret and Golfari in Venezuela. Agronomiá Tropical (Maracay), 45(4):473-481; 9 ref.

Selander J; Bubala M, 1983. A survey of pest insects in forest plantations in Zambia. Kitwe, Zambia: Division of Forest Research, 33 pp.

South Africa; Institute for Commercial Forestry Research, 1987. Forest protection. Annual Report, Institute for Commercial Forestry Research, University of Natal, 25-33, s. 2-3

Tremblay E, 1975. The parasites of the aphids of Pinus nigra Arn. (Hymenoptera Ichneumonoidea). Bollettino del Laboratorio di Entomologia Agraria 'Filippo Silvestri', Portici, 32:91-110

Tremblay E; DeBiase LM, 1970. Notulae aphidologicae II. - Notizie sugli afidi del Pinus nigra Arn. (Aphidological notes II. - Notes on the aphids of Pinus nigra Arn.). Bollettino del Laboratorio di Entomologia Agraria Filippo Silvestri Portici, 28: 204-223.

Zondag R, 1983. Eulachnus brevipilosus Borner (Hemiptera: Aphididae). Pine aphid. Forest and Timber Insects in New Zealand, No. 55:4 pp.

Distribution Maps

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