Acyrthosiphon pisum

(Harris, 1776)

Pea aphid, green dolphin, pea louse, clover louse

, the , is a sap-sucking hemipteran and major agricultural pest of legume crops worldwide. It is notable as the first hemimetabolous insect with a fully sequenced and serves as a model organism for studying , endosymbiosis, , and . The exhibits complex polyphenism with multiple morphs including winged and wingless parthenogenetic females, sexual males and females, and green or red/pink color morphs. Its survival depends entirely on the obligate endosymbiont Buchnera aphidicola, which provides lacking in its phloem sap diet.

Acyrthosiphon pisum by (c) Mihajlo Tomić, some rights reserved (CC BY), uploaded by Mihajlo Tomić. Used under a CC-BY license.

HEMI Aphididae Acyrthosiphon pisum by Desmond W. Helmore
. Used under a CC BY 4.0 license.

Acyrthosiphon pisum 2200056 by Whitney Cranshaw, Colorado State University. Used under a CC BY 3.0 us license.

Pronunciation

How to pronounce Acyrthosiphon pisum: /əˌsɜːrθəˈsɪfɒn ˈpaɪsəm/

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Identification

Distinguished from the blue alfalfa (Acyrthosiphon kondoi) by: (1) bright green versus blue-green coloration, (2) larger body size, and (3) with dark bands at segment tips versus uniformly dark antennae. Distinguished from other alfalfa aphids by size (largest in alfalfa at up to 4 mm) and antennal banding pattern. Cowpea aphid (Aphis craccivora) is dark blue-black with off-white legs having black tips. Spotted alfalfa aphid (Therioaphis trifolii) is smaller (1/16 inch), grayish-yellow to yellow-green with four to six rows of raised dark spots on the back.

Images

Appearance

are relatively large aphids, reaching up to 4 mm in body length. Body color is variable, occurring as green or red/pink morphs with hereditary basis; green morphs predominate in natural . The body is soft-bodied and elongate. are long with dark bands at the tips of each segment, distinguishing it from the blue alfalfa (Acyrthosiphon kondoi) which has uniformly dark antennae. Cornicles (siphunculi), the paired abdominal tubes characteristic of aphids, are present. Winged morphs have fully developed wings; wingless morphs lack wings.

Habitat

Found on cultivated legume crops and wild legume in agricultural fields, meadows, and grasslands. Occurs on lower sides of leaves, buds, and pods of host plants. Does not form dense colonies where individuals remain sedentary throughout life; shows more dispersed distribution than many . Not known to be tended by ants. Temperature and day length influence morph production and .

Distribution

Native to the Palearctic region; now in temperate climates worldwide. Introduced to North America likely during the 1870s, established as a serious pest in mid-Atlantic states by 1900, and widespread throughout the United States and Canada by the 1950s. Present in Europe (including Scandinavia, Mediterranean, and Atlantic islands), Asia (Middle East, Central Asia, East Asia, South Asia), Africa (North, East, and South), Australasia (Australia, New Zealand, Hawaii), and South America (Argentina, Bolivia, Brazil, Chile, Peru, Uruguay, Venezuela). Distribution closely tied to and introduction of legume crops.

Seasonality

as fertilized laid by sexual females in autumn, hatching in spring. Parthenogenetic dominates spring through summer, with densities highest in early summer. Sexual morphs (males and females) produced in autumn triggered by lengthening nights and cooler temperatures. Winged females produced when colonies become overcrowded or quality declines, dispersing to new plants. Complete reproductive cycle can occur without .

Diet

Obligate phloem feeder, ingesting phloem sap through piercing-sucking stylets. Feeds on lower sides of leaves, buds, and pods. range encompasses more than 20 legume (Fabaceae), including: Pisum sativum (pea), Medicago sativa (alfalfa), Trifolium pratense (red clover), Trifolium spp. (clover), Vicia faba (broad bean), Lens culinaris (lentil), Cicer arietinum (chickpea), Lupinus spp. (lupin), Vigna spp., and other pulse crops. Phloem sap is nutritionally rich in but deficient in nitrogen and ; this deficiency is compensated by the obligate endosymbiont Buchnera aphidicola.

Host Associations

Pisum sativum - pea
Medicago sativa - alfalfa
Trifolium pratense - red clover
Trifolium spp. - clover
Vicia faba - broad bean, fava bean
Lens culinaris - lentil
Cicer arietinum - chickpea
Lupinus spp. - lupin
Buchnera aphidicola - obligate endosymbiontPrimary bacterial endosymbiont housed in specialized bacteriocytes; provides and is necessary for . Transmitted vertically from mother to offspring. Coevolved for 160-280 million years.
Hamiltonella defensa - facultative endosymbiontSecondary ; retards development of
Serratia symbiotica - facultative endosymbiontSecondary ; retards development of , provides heat stress
Regiella insecticola - facultative endosymbiontSecondary ; decreases mortality from fungal Pandora neoaphidis

Life Cycle

Hemimetabolous development with complex . : fertilized laid by sexual females in autumn, entering . Spring : nymphs hatch from eggs, all female, undergo four before sexual maturity. Summer : by unmated females, producing 4-12 female nymphs daily (~100 per lifetime); nymphs develop to mature females in 7-10 days; lifespan ~30 days. Autumn transition: shortened day length triggers production of sexual morphs (winged males and females) by parthenogenetic females; mating occurs, females lay overwintering eggs. Winged morphs: produced under crowding or poor food quality for . Multiple overlapping per year in favorable conditions.

Behavior

Exhibits , with first and second instar nymphs showing negative binomial distribution on feeding stations; aggregation more pronounced under light than darkness, not dependent on visual contact with other aphids. Displays escape behavior in response to and vibration stimuli. Avoids inbreeding through kin recognition; close-kin mating results in reduced hatching success and offspring survival. via winged females produced under crowded conditions. Does not form dense sedentary colonies; individuals move more than in many . Not -tended; does not produce abundant honeydew.

Ecological Role

Herbivore and agricultural pest; weakens plants through sap removal, causing leaf curling, wilting, and stunted growth. of over 30 plant viruses including cucumber mosaic virus and beet yellows virus, transmitting during feeding. Honeydew promotes growth, reducing . Serves as prey for diverse natural enemies including lady beetles (Coccinellidae), (Aphidius ervi, Aphidius smithi, Praon pequodorum), and fungi (Erynia neoaphidis, Pandora neoaphidis). Supports complex multitrophic interactions involving bacterial endosymbionts that mediate parasitoid resistance. As a model organism, contributes to fundamental understanding of insect-plant interactions, , and evolutionary .

Human Relevance

Major agricultural pest of legume crops worldwide, particularly damaging to peas, alfalfa, clover, lentils, chickpeas, and fava beans. Economic impact through direct feeding damage (yield reduction, quality loss), virus transmission, and honeydew/ . Management relies primarily on chemical (flonicamid, spirotetramat registered in North America); no documented insecticide resistance as of current sources. Cultural controls include cultivars, early seeding, with cereals or mustard, and manipulation. using lady beetles, , and fungi shows promise but requires further field evaluation. Model organism for genomic, developmental, and evolutionary research; first hemimetabolous insect sequenced (525 Mb, ~34,000 genes). Important for studying bacterial , , , and biosynthesis (one of few animals capable of synthesizing carotenoids via from fungi).

Similar Taxa

Acyrthosiphon kondoiBlue alfalfa ; distinguished by blue-green color, smaller size, and uniformly dark without segmental banding. range very similar in North America.
Aphis craccivoraCowpea aphid; distinguished by dark blue-black shiny color, off-white legs with black tips, and toxic saliva causing distinct plant .
Therioaphis trifoliiSpotted alfalfa aphid; distinguished by smaller size, grayish-yellow color, and four to six rows of raised dark spots on the back.

More Details

Model Organism Status

Premier model for biological research due to easily completed reproductive cycle under laboratory conditions, relatively large size facilitating physiological studies, and sequenced (2010, International Aphid Consortium). First genome of a hemimetabolous insect published. Enables research on , , , biosynthesis, and .

Species Complex

encompasses multiple described as cryptic , , or races specialized on different species. Host-associated differentiation drives ecological speciation within the complex.

Carotenoid Biosynthesis

One of few animals known to synthesize , producing torulene (3',4'-didehydro-β,γ-carotene) via of fungal carotenoid synthesis genes. Red coloration from torulene may aid in camouflage and avoidance.

Reduced Immune System

lacks key immune response genes including IMD components (IMS, dFADD, Dredd, Retish) and antimicrobial genes. Reduced may facilitate maintenance of Buchnera and reflects low microbial exposure in phloem sap diet.

Metabolic Complementarity with Buchnera

Joint metabolic between and endosymbiont complete biosynthesis of essential nutrients. A. pisum lacks urea cycle and purine salvage pathway genes; Buchnera compensates. Aphid contributes degradation genes while Buchnera retains biosynthesis genes. No lateral detected between partners.