Rhagoletis completa (walnut husk fly)
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- Risk of Introduction
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Vectors
- Plant Trade
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Rhagoletis completa Cresson
Preferred Common Name
- walnut husk fly
Other Scientific Names
- Rhagoletis suavis completa Cresson
- Rhagoletis suavis var. completa Cresson
International Common Names
- English: husk maggot
- French: mouche des brous du noyer
Local Common Names
- : husk maggot
- Germany: Amerikanische Walnussschalen-Fliege; Fliege, Amerikanische Walnussschalen
- RHAGCO (Rhagoletis completa)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Diptera
- Family: Tephritidae
- Genus: Rhagoletis
- Species: Rhagoletis completa
Notes on Taxonomy and NomenclatureTop of page R. completa was originally described as a subspecies of R. suavis but these have been recognized as separate species since the 1930s (see Foote et al., 1993).
DescriptionTop of page Adult
Diagnostic features of the genus are as follows (characters extracted from key to North American genera of Tephritidae by Foote et al., 1993): Head with two pairs orbital setae; posterior pair reclinate. Gena with only short anterior setae. First flagellomere (third antennal segment) at least slightly pointed at the apex. Thorax with dorsocentral setae closer to level of anterior supra-alar setae than transverse suture. Scutellum not swollen or shiny. Wing with cells bm and bcu of similar depth; bcu with a short acute extension. Crossvein R-M near middle of cell dm.
This species may be identified using the Diptera key in the Crop Protection Compendium taxonomic identification aid. For full details of its separation from other North American species, see Foote et al. (1993).
The main features of R. completa are as follows: thorax and abdomen predominantly pale yellow to orange. Wing with a distinct subbasal crossband; discal and preapical crossbands usually separate. Mediotergite dark marked (either entirely dark brown or with a pair of brown stripes). For more comprehensive details see Foote et al. (1993).
Diagnosis of genus by Elson-Harris (White and Elson-Harris, 1994): Antennal sensory organ with a short basal segment and cone-shaped distal segment; maxillary sensory organ flat, with well defined sensilla surrounded by small cuticular folds; stomal sensory organ rounded, with a peg-like sensilla; large, preoral teeth near base of stomal sensory organ; no preoral lobes; oral ridges in 5-13 short, unserrated rows; no accessory plates. Stout spinules forming discontinuous rows on almost all segments. Anterior spiracles with 7-35 stout tubules. Posterior spiracular slits 3-8 times as long as broad, with 3-16 short, branched spiracular hairs. Anal lobes large, protuberant with well defined tubercles and sensilla.
There is no modern description of the larva of this species (in the sense of SEM studies being applied). However, Steyskal (1973) provided a key for the separation of the larvae of three species found in walnut. Any Rhagoletis larvae found in walnuts and having the following features is likely to be this species: 16-21 tubules, in each anterior spiracle; upper and lower slits of the posterior spiracles at about 60 degrees to each other. See key to larvae in White and Elson-Harris (1994), which used a combination of host and fragmentary morphological data.
DistributionTop of page R. completa is native to southern and central USA; adventive in western USA since the 1920s (Bush, 1966). Also adventive in southern Europe since the early 1990s (Ciampolini and Trematerra, 1992; Merz, 1994; Seljak and Zezlina, 1999).
Harris (1989), Foote et al. (1993) and CABI (1997) all provide distribution maps.
Distribution TableTop of page
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 IntroductionTop of page R. completa poses a small quarantine risk for temperate regions. However, now that it is established in Switzerland and Italy, this species has been removed from the European and Mediterranean Plant Protection Organization (EPPO) A1 list. However, there are no practical measures to prevent its spread and it is not considered to be a very important pest, so EPPO recently decided not to add it to its A2 list. It has not been individually considered to be a quarantine pest by any other Regional Plant Protection Organization.
HabitatTop of page Areas with suitable hosts and climate.
Hosts/Species AffectedTop of page R. completa is mainly associated with Juglans species. It is also known to attack Prunus persica (peach) (Bush, 1966).
Host Plants and Other Plants AffectedTop of page
Growth StagesTop of page Fruiting stage
SymptomsTop of page Attacked fruit will be pitted by oviposition punctures, around which some discoloration usually occurs.
List of Symptoms/SignsTop of page
|Fruit / discoloration|
|Fruit / extensive mould|
|Fruit / gummosis|
|Fruit / internal feeding|
|Fruit / lesions: black or brown|
|Fruit / lesions: scab or pitting|
|Fruit / obvious exit hole|
|Fruit / odour|
|Fruit / ooze|
Biology and EcologyTop of page Most Rhagoletis species have a similar biology as detailed by Christenson and Foote (1960): eggs are laid below the skin of the host fruit and hatch after 3-7 days; the larvae usually feed for 2-5 weeks; pupariation is in the soil under the host plant and this is the normal overwintering stage; adults may live for up to 40 days under field conditions. In Oregon, adults emerge from late June to mid-August or sometimes early September; peak oviposition is in late August (Kasana and Aliniazee, 1996).
For development rates at various temperatures see Kasana and AliNiazee (1994).
Natural enemiesTop of page
Notes on Natural EnemiesTop of page The braconid, Biosteres sublaevis, and a eucoilid of the genus Trybliographa, were found to cause varying degrees of natural parasitism in New Mexico (Legner and Goeden, 1987).
Means of Movement and DispersalTop of page Adult flight and the transport of infected fruit are the major means of movement and dispersal to previously uninfected areas. However, Rhagoletis species are not known to fly more than a short distance (Fletcher, 1989). In international trade, the major means of dispersal to previously uninfested areas is the transport of fruit containing live larvae. There is also a risk from the transport of puparia in soil or packaging with plants which have already fruited.
Pathway VectorsTop of page
|Clothing, footwear and possessions||Fruit in case or handbag.||Yes|
|Containers and packaging - wood||Of fruit cargo.||Yes|
|Land vehicles||Lorries, aeroplanes and perhaps ships, with fruit cargo.||Yes|
|Fruit in post.||Yes|
|Soil, sand and gravel||Risk of puparia in soil.||Yes|
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Fruits (inc. pods)||eggs; larvae||Yes||Pest or symptoms usually visible to the naked eye|
|Growing medium accompanying plants||pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Plant parts not known to carry the pest in trade/transport|
|Stems (above ground)/Shoots/Trunks/Branches|
|True seeds (inc. grain)|
ImpactTop of page In North America, R. completa is a pest of various Juglans species but it has rarely been recorded on European walnut (J. regia). In Switzerland, it attacks the mesocarp of J. regia, and in the case of severe infestation may also damage the pericarp and the nut itself (R. Mani, Switzerland [address available from CABI], personal communication, 2001). It therefore becomes a problem for walnut fruit production. In 1991, 50% of harvested walnuts in some Italian orchards were infested by R. completa (Ciampolini and Trematerra, 1992). In Oregon, Kasana and Aliniazee (1996) recorded up to 95% infestation on untreated trees.
In California it causes two types of damage. In populations causing normal or late-season infestations, larval feeding causes the whole husk or large portions of it to turn black, seriously reducing the value of nuts sold in the shell although the kernel is undamaged. Attack by populations involved in early infestations impedes the maturation of the kernel and results in shrivelled nuts or empty shells (Hislop et al., 1981).
DiagnosisTop of page
EPPO (2011) describes a diagnostic protocol for R. completa infesting walnuts.
Detection and InspectionTop of page Traps have been developed which capture both sexes, based on visual, or visual plus odour, attraction. They are coated in sticky material and are usually either flat-surfaced and coloured fluorescent yellow to elicit a supernormal foliage response (see Riedl et al., 1989), or spherical and dark-coloured to represent a fruit (green spheres are best, see Riedl and Hislop, 1985); traps which combine both foliage and fruit attraction can also be used. The odour comes from protein hydrolysate or other substances emitting ammonia, such as ammonium acetate. See Boller and Prokopy (1976) and Economopoulos (1989) for a discussion of these traps.
Similarities to Other Species/ConditionsTop of page This species should not be mistaken for any other provided the diagnostic notes (see Morphology) are applied carefully. If in doubt consult Foote et al. (1993). R. suavis is an eastern USA species which is also associated with Juglans species, and in the past has been confused with R. completa (see Distribution Section).
Prevention and ControlTop of page
Upon detection, fallen and infected fruit must be removed and destroyed. If possible, wild and abandoned host trees should also be destroyed. Boller and Prokopy (1976) note that systemic organophosphates, such as dimethoate, are highly effective against most species, killing eggs, larvae and adults. Belanger et al. (1985) discussed the use of pyrethroids, but these were only of use when pest activity was low. More environmentally acceptable techniques have been tried; namely bait sprays (insecticide plus ammonia source) which can be applied as a spot treatment; soil application of insecticide to destroy pupae; and juvenile hormone analogues which can be applied to the soil (Boller and Prokopy, 1976). The IPM of walnut pests, including R. completa, was discussed by Haley and Baker (1982). Early harvest can be used to avoid attack (Yokoyama and Miller, 1996). Some varieties may be more susceptible to attack than others. Shelton and Anderson (1990) compared four varieties and found that Hartley suffered less damage than early leafing varieties.
Consignments of fruits from countries where these pests occur should be inspected for symptoms of infestation and those suspected should be cut open in order to look for larvae. European and Mediterranean Plant Protection Organization (EPPO) recommended (OEPP/EPPO, 1990), when only the North American origin was under consideration, that such fruits should come from an area where R. completa does not occur or from a place of production subject to growing season inspection. Fruits may also be treated in transit by cold treatment (for example, 40-42 days at -0.6°C) (FAO, 1983); however, Yokoyama and Miller (1996) found that low temperature storage could not be used as a quarantine treatment alone for some crops (e.g. walnuts) because the fly tolerated the treatment better than the host. Ethylene dibromide was previously widely used as a fumigant but is now generally withdrawn because of its carcinogenicity. Treatment methods against fruit flies are currently under review within EPPO and as part of an inter-RPPO programme.
Plants of host species transported with roots from countries where these pests occur should be free from soil, or the soil should be treated against puparia. The plants should not carry fruits. Such plants may indeed be prohibited from importation.
ReferencesTop of page
Armstrong JW; Couey HM, 1989. Control; fruit disinfestation; fumigation, heat and cold. In: Robinson AS, Hooper G, eds. Fruit Flies; their Biology, Natural Enemies and Control. World Crop Pests. Amsterdam, Netherlands: Elsevier, 3(B):411-424.
Boller EF; Prokopy RJ, 1976. Bionomics and management of Rhagoletis. In: Smith RF, Mittler TE, Smith CN, ed. Annual review of entomology. Volume 21. Annual Reviews Inc. Palo Alto, California, USA, 223-246.
Bush GL, 1966. The taxonomy, cytology and evolution of the genus Rhagoletis in North America (Diptera: Tephritidae). Bulletin of the Museum of Comparative Zoology, 134:431-526.
Christenson LD; Foote RH, 1960. Biology of fruit flies. Annual Review of Entomology, 5:171-192.
Economopoulos AP, 1989. Control; use of traps based on color and/or shape. In: Robinson AS, Hooper G, eds. Fruit Flies; Their Biology, Natural Enemies and Control. World Crop Pests 3(B): 315-327. Amsterdam, Netherlands: Elsevier.
EPPO, 1990. Specific quarantine requirements. EPPO Technical Documents, No. 1008. Paris, France: European and Mediterranean Plant Protection Organization.
EPPO, 2011. EPPO Reporting Service. EPPO Reporting Service. Paris, France: EPPO. http://archives.eppo.org/EPPOReporting/Reporting_Archives.htm
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
EPPO, 2016. EPPO Global database (available online). Paris, France: EPPO. https://gd.eppo.int/
European and Mediterranean Plant Protection Organization, 2011. Diagnostics: Rhagoletis completa. Bulletin OEPP/EPPO Bulletin, 41(3):357-362. http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2338
FAO, 1983. International plant quarantine treatment manual. FAO Plant Production and Protection Paper No. 50. Rome, Italy: FAO.
Fletcher BS, 1989. Ecology; movements of tephritid fruit flies. In: Robinson AS, Hooper G, eds. Fruit Flies; Their Biology, Natural Enemies and Control. World Crop Pests, 3(B). Amsterdam, Netherlands: Elsevier, 209-219.
Foote RH, 1981. The genus Rhagoletis Loew south of the United States (Diptera: Tephritidae). Technical Bulletin, Science and Education Administration, United States Department of Agriculture, No. 1607:iv + 75 pp.
Foote RH; Blanc FL; Norrbom AL, 1993. Handbook of the Fruit Flies (Diptera: Tephritidae) of America North of Mexico. Ithaca, USA: Comstock.
Haley MJ; Baker L, ed. , 1982. Integrated pest management for walnuts. Integrated pest management for walnuts. University of California Statewide Integrated Pest Management Project Berkeley USA, 96 pp.
Harris EJ, 1989. Pest status; Hawaiian Islands and North America, In: Robinson AS, Hooper G, eds. Fruit Flies; their Biology, Natural Enemies and Control. World Crop Pests. Amsterdam, Holland: Elsevier, 3(A):73-81.
IPPC, 2013. First report of Rhagoletis completa. IPPC Official Pest Report, No. HUN-02/1. Rome, Italy: FAO. https://www.ippc.int/
IPPC, 2016. First suspicion of Rhagoletis completa on Juglans regia in a private garden. IPPC Official Pest Report, No. NLD-46/1. https://www.ippc.int/en/
Legner EF; Goeden RD, 1987. Larval parasitism of Rhagoletis completa (Diptera: Tephritidae) on Juglans microcarpa (Juglandaceae) in western Texas and southeastern New Mexico. Proceedings of the Entomological Society of Washington, 89(4):739-743
Ostojic I; Zovko M; Petrovic D, 2014. First record of walnut husk fly Rhagoletis completa (Cresson, 1929) in Bosnia and Herzegovina. (Prvi nalaz orahove muhe Rhagoletis completa (Cresson, 1929) u Bosni i Hercegovini.) Radovi Poljoprivrednog Fakulteta Univerziteta u Sarajevu (Works of the Faculty of Agriculture University of Sarajevo), 59(64(1)):121-126.
Riedl H; Barnett WW; Coates WW; Coviello R; Joos J; Olson WH, 1989. Walnut husk fly (Diptera: Tephritidae): evaluation of traps for timing of control measures and for damage predictions. Journal of Economic Entomology, 82(4):1191-1196
Rull J; Tadeo E; Aluja M; Guillen L; Egan SP; Feder JL, 2012. Hybridization and sequential components of reproductive isolation between parapatric walnut-infesting sister species Rhagoletis completa and Rhagoletis zoqui. Biological Journal of the Linnean Society, 107(4):886-898. http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1095-8312
Seljak G; Zezlina I, 1999. Appearance and distribution of walnut husk fly (Rhagoletis completa Cresson) in Slovenia. Zbornik predavanj in referatov 4. Slovenskega Posvetovanja o Varstvu Rastlin v Portoroz^hacek~u od 3. do 4. Marca 1999., 231-238; 7 ref.
Steyskal GC, 1973. Distinguishing characters of the walnut husk maggots of the genus Rhagoletis (Diptera, Tephritidae). Cooperative Economic Insect Report, 23: 522.
Tuba K; Schuler H; Stauffer C; Lakatos F, 2012. First record of the walnut husk fly (Rhagoletis completa Cresson 1929) (Diptera: Tephritidae) in Hungary. (A nyugati dióburok-fúrólégy (Rhagoletis completa Cresson 1929 - Diptera: Tephritidae) megjelenése magyarországon.) Növényvédelem, 48(9):419-424.
Yokoyama VY; Miller GT, 1996. Response of walnut husk fly (Diptera: Tephritidae) to low temperature, irrigation, and pest-free period for exported stone fruits. Journal of Economic Entomology, 89(5):1186-1191; 7 ref.
Distribution MapsTop of page
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