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Comprehensive Overview of Major Onion Pests Worldwide and Characteristic Damage Symptoms ​

Overview ​

Onion (Allium cepa) is an important vegetable crop grown worldwide, but damage from diverse pests seriously affects yield and quality. This overview details major onion pests recognized internationally regardless of region or cultivation environment, including scientific and common names, distribution and occurrence, characteristic damage symptoms for identification, and distinctive biological aspects. Regional differences and unresolved points are also noted, based on reliable international and academic sources.

Major Onion Pests and Their Characteristics ​

1. Onion Thrips (Thrips tabaci) ​

  • Scientific and common names: Thrips tabaci (onion thrips)
  • Distribution and occurrence: One of the most important onion pests worldwide. Mediterranean origin but now distributed in nearly all onion production regions including North America, Europe, Asia, Africa, South America, and Australia. Increasing importance with insecticide resistance and range expansion [1][2][3][4][5][6][7].
  • Damage symptoms:
    • Sap feeding causes white to silver spots and streaks, black fecal spots, leaf tip death, poor growth, and bulb enlargement inhibition
    • Under outbreak conditions, heart death and whole-plant death may occur
    • With virus transmission (IYSV: Iris yellow spot virus): straw to brown spindle or diamond-shaped lesions, yellowing spots
  • Biological characteristics:
    • Explosive increase under drought and high temperature; 6–10 generations per year; mainly parthenogenetic
    • Eggs laid inside leaf tissue; short life cycle (3–4 weeks); multiple generations and high reproductive capacity
    • Problematic due to pesticide resistance development and IYSV vector capability
    • May reduce total crop yield by more than 50%; damage can be severe [3][4][5][7][9].

2. Onion Maggot and Seedcorn Maggot ​

  • Scientific and common names:
    • Onion maggot: Delia antiqua
    • Seedcorn maggot: Delia platura
  • Distribution and occurrence:
    • Major pests in temperate North America and Europe. Distributed worldwide; also reported in Far East including Japan, Central Asia, and Oceania.
    • Seedcorn maggot is polyphagous and widely distributed [13][14].
  • Damage symptoms:
    • Larvae bore into roots and bulbs; stem base feeding causes wilting, collapse, and plant death
    • Devastating stand loss and damping-off soon after germination; boring and feeding inside bulbs in soil causes rot and softening
  • Biological characteristics:
    • Onion maggot: pupates in soil and overwinters; three generations per year; prefers cool, moist conditions
    • Seedcorn maggot: frequent in fields with abundant organic matter residues
    • Control basics include rotation and integrated management including nematicides [13][14].

3. Cutworms (Agrotis ipsilon, Peridroma saucia) ​

  • Scientific and common names: Agrotis ipsilon (black cutworm), Peridroma saucia (variegated cutworm)
  • Distribution and occurrence: Distributed in vegetable fields and turf worldwide. Recognized in onion production regions in North America, Europe, Asia, Africa, and Oceania [15][16][17].
  • Damage symptoms:
    • Nocturnal activity; cut seedling stems at ground level (stand loss, sudden plant death)
    • Mature larvae may bore into bulb portions; feeding marks and holes near soil surface
  • Biological characteristics:
    • Adults are nocturnal flying moths
    • Pupate in soil or crop debris and overwinter; 2–4 generations per year
    • Increased occurrence in weedy fields and rotation with cereals
    • Control includes tillage, weed removal, and insecticides [15][16][17].

4. Armyworms (Spodoptera exigua, S. litura, etc.) ​

  • Scientific and common names: Spodoptera exigua (beet armyworm), Spodoptera litura (common cutworm), Mamestra configurata, etc.
  • Distribution and occurrence: S. exigua and S. litura are widely distributed in Asia, North America, Europe, and Oceania. Occurrence varies greatly by year and region; severe onion damage in outbreak years [18][19][20][21].
  • Damage symptoms:
    • Group leaf feeding creates large holes and leaf death; "skeletonized" leaf midribs
    • Under major outbreaks, all green foliage may disappear; bulbs also damaged
  • Biological characteristics:
    • Nocturnal egg laying and feeding; eggs in masses on leaf undersides
    • Pupate in soil; egg to adult in 3.5–4 weeks
    • Increased occurrence with organic inputs, lush growth, and weedy areas. Physical management including natural enemies, microbial insecticides, tillage, and residue removal is important [18][19][21].

5. Leek Moth (Acrolepiopsis assectella) ​

  • Scientific and common names: Acrolepiopsis assectella (leek moth)
  • Distribution and occurrence: European origin. Recently established in eastern North America and northern Canada. Expanding in temperate zones; detailed global distribution not fully clarified [23].
  • Damage symptoms:
    • Larvae bore into leaves and bulbs; frass trails, windowpane feeding marks
    • Under heavy infestation, entire bulbs may be damaged or destroyed
  • Biological characteristics:
    • Nocturnal moth; multiple generations per year
    • Re-invasion from weeds and field margin vegetation requires attention [23].

6. Allium Leafminer (Phytomyza gymnostoma) ​

  • Scientific and common names: Phytomyza gymnostoma (allium leafminer)
  • Distribution and occurrence: Expanded in Europe and the UK; invaded northeastern North America after 2015. Emerging pest with future expansion concern [23].
  • Damage symptoms:
    • Larvae create curved mines in leaves and bulb leaf sheaths
    • Abnormal leaf twisting and shrinkage; bulb rot from secondary pathogens
  • Biological characteristics:
    • Female flies lay eggs inside leaves. 1–2 generations
    • Difficult to manage after establishment; control is challenging in invaded regions [23].

7. Bulb Mites and Storage Pests (Rhizoglyphus spp., Carpophilus, Lasioderma, etc.) ​

  • Scientific and common names: Rhizoglyphus spp. (bulb mites), Carpophilus spp. (sap beetles), Lasioderma serricorne (cigarette beetle), etc.
  • Distribution and occurrence: Distributed in fields and storage facilities worldwide. Bulb mites frequent in poorly managed fields rich in organic matter. Includes post-harvest storage pests [24].
  • Damage symptoms:
    • During storage: bulb depressions, soft rot, dry rot, appearance quality decline
    • Multi-pore marks from mites and beetles; increased cold rot
  • Biological characteristics:
    • Reproduce under humid, high-temperature conditions; removal, cleaning, and pre-harvest sanitation are essential [24].

Regional Differences and Data Limitations ​

  • Leek moth and allium leafminer are still emerging pests in limited regions but may become major pests with expansion.
  • Cutworms and armyworms are often recognized as major pests only in certain years or outbreak years; regional variation in occurrence is large.
  • Notable international lists cite 149 insect species in 11 orders damaging onion; leaf feeding predominates (69.1%) while root and bulb feeding also causes economic loss [24][25].
  • Accurate grasp of occurrence and regional comparison of economic damage remain unclear in many areas due to differences in survey systems and records.

Conclusion ​

Major pests in onion cultivation are broadly classified as thrips, onion maggot flies, cutworms, armyworms, leafminers and leek moth, and bulb mites/storage pests. All are distributed globally or expanding, and can have devastating effects in fields and storage when they occur. Damage symptoms are characteristic: early stand loss and damping-off, leaf spots/necrosis/boring, and bulb soft rot/dry rot. Early field identification is important for building appropriate control and management. Flexible integrated management is increasingly needed amid pesticide resistance and invasion/expansion of new pests.

Sources ​

[1] Utah State University Extension - Onion Thrips: https://extension.usu.edu/pests/research/onion-thrips.php
[2] Koppert Canada - Onion Thrips: https://www.koppert.ca/plant-pests/thrips/onion-thrips/
[3] Journal of Economic Entomology - Onion Thrips: A Global Pest of Increasing Concern in Onion: https://pubmed.ncbi.nlm.nih.gov/21404832/
[4] Journal of Integrated Pest Management - Onion Thrips Biology, Ecology, and Management: https://academic.oup.com/jipm/article/6/1/6/2936974
[5] Minnesota University Extension - Onion Thrips: https://ncipmhort.cfans.umn.edu/sites/ncipmhort.cfans.umn.edu/files/2022-03/Onion_Thrips.pdf
[6] University of Florida - Onion Thrips: https://mrec.ifas.ufl.edu/lso/entomol/NCSTATE/thrips9.htm
[7] PDF - Onion Thrips: A Global Pest (ResearchGate): https://real.mtak.hu/20171/1/2011_JEE.pdf
[8] Washington State University - Onion/Allium Problem Gallery: https://mtvernon.wsu.edu/path_team/photo-gallery-of-vegetable-problems/onion-allium/
[9] NIH - Managing insect and plant pathogen pests organically: https://pmc.ncbi.nlm.nih.gov/articles/PMC10711546/
[10] NC State Extension - Pests of Onion: https://content.ces.ncsu.edu/insect-and-related-pests-of-vegetables/pests-of-onion
[11] ResearchGate - Onion Thrips: A Global Pest: https://www.researchgate.net/publication/50396900_Onion_Thrips_Thysanoptera_Thripidae_A_Global_Pest_of_Increasing_Concern_in_Onion
[12] Bohrium - Onion Thrips: https://www.bohrium.com/paper-details/onion-thrips-thysanoptera-thripidae-a-global-pest-of-increasing-concern-in-onion/811678295903961088-1481
[13] Cornell University - Onion maggot and seedcorn maggot: https://cals.cornell.edu/integrated-pest-management/outreach-education/fact-sheets/onion-maggot-and-seedcorn-maggot-delia-antiqua-and-delia-platura
[14] UMass Extension - Major Insect Pests of Onion (PDF): https://www.umass.edu/agriculture-food-environment/sites/ag.umass.edu/files/pdf-doc-ppt/allium_insect_disease_5.25.2021.pdf
[15] Lucidcentral - Armyworms & Cutworms: https://keys.lucidcentral.org/keys/sweetpotato/key/Sweetpotato Diagnotes/Media/Html/TheProblems/Pest-LeafChewingInsects/ArmyWorms/Armyworms.htm
[16] PNW Handbooks - Onion Armyworm & Cutworm: https://pnwhandbooks.org/insect/vegetable/vegetable-pests/hosts-pests/onion-armyworm-cutworm
[17] Colorado State University - Armyworm and Cutworms: https://agsci.colostate.edu/agbio/ipm-pests/armyworm-and-cutworms/
[18] Kyushu University - Insect Pests Attacking Green Bunching Onion: https://api.lib.kyushu-u.ac.jp/opac_download_md/9242/p275.pdf
[19] ResearchGate - Beet Armyworm Emerging Threat: https://www.researchgate.net/publication/342097368_Beet_Armyworm_Spodoptera_exigua_Emerging_Threat_to_Onion_Production
[20] Academia.edu - Checklist of Insect Pests of Onion: https://www.academia.edu/85320055/A_checklist_of_insect_pests_of_onion
[21] Utah State University - Armyworm and Cutworms in Turfgrass: https://extension.usu.edu/pests/ipm/notes_orn/list-turf/armyworm-cutworm
[22] Noble Research Institute - Fall Armyworms (YouTube): https://www.youtube.com/watch?v=TjrdnEJQlwA
[23] UMass Extension - Major Insect Pests of Onion (PDF): https://www.umass.edu/agriculture-food-environment/sites/ag.umass.edu/files/pdf-doc-ppt/allium_insect_disease_5.25.2021.pdf
[24] ResearchGate - A Checklist of Insect Pests of Onion: https://www.researchgate.net/publication/359502526_A_Checklist_of_Insect_Pests_of_Onion
[25] Wikifarmer - Major Onion Pests and Sustainable Management: https://wikifarmer.com/library/en/article/major-onion-pests-and-diseases-and-sustainable-management-practices

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