Lucerne Aphid
Acyrthosiphon pisum
📖 Description
Acyrthosiphon pisum, the Pea Aphid or Lucerne Aphid, is a large polyphagous aphid pest of leguminous crops worldwide. The species is holocyclic (sexual reproduction in autumn) in temperate regions but anholocyclic (parthenogenetic year-round) in tropical India, allowing rapid population build-up without the constraint of egg over-wintering. A single foundress can produce 80–120 nymphs in her 30-day lifespan, and each nymph reaches reproductive maturity in just 8–10 days — under favourable conditions, an aphid population can increase 10-fold per week. This biological capacity means that aphid outbreaks can develop within days of initial colonisation, making preventive conservation of natural enemies the foundation of sustainable management. India’s lucerne (alfalfa) cultivation is concentrated in the north-western plains (Punjab, Haryana, western Uttar Pradesh) where the crop is grown as a perennial fodder for dairy animals, with smaller plantations in Maharashtra, Tamil Nadu, and the hill states. Lucerne is unusual among Indian fodders in being a perennial — a stand can remain productive for 4–6 years, providing 6–8 cuttings per year. This permanence makes lucerne fields ideal reservoirs for aphid populations, which can build up over multiple seasons if natural enemies are suppressed by insecticide use. The pest is particularly damaging in spring (March–May) when temperatures rise to the aphid’s optimum range (20–25 °C) and the lucerne crop is at peak vegetative growth. IPM packages developed by IGFRI Jhansi emphasise natural-enemy conservation, early cutting at the economic threshold, and balanced nutrition as the core management tactics.
⚠️ Symptoms to watch for
- Curling and yellowing of leaves — the early symptom
- stunting of new shoots
- reduced flowering and seed set
- sooty mould growth on honeydew excreted on lower leaves
- plant decline under heavy infestation.
- In lucerne fodder crops in Punjab, Haryana, Uttar Pradesh, and Maharashtra, heavy infestation can reduce green-fodder yield by 20–35 % and reduce the protein content of the forage by 10–15 %, directly affecting milk production in dairy animals fed the infested fodder.
🩹 Treatment
- Cultural: cut the lucerne crop early when aphid populations exceed the economic threshold (10 aphids per stem)
- conserve natural enemies by avoiding broad-spectrum insecticides.
- Biological: release Chrysoperla zastrowi (green lacewing) larvae at 5,000/ha
- apply Beauveria bassiana at 5 g/L.
- Chemical: spray imidacloprid 17.8 SL @ 0.3 ml/L or dimethoate 30 EC @ 1.5 ml/L — both effective systemic insecticides
- pymetrozine 50 WG @ 0.5 g/L is a selective aphicide that conserves natural enemies.
🌿 Organic treatments
- Spray neem oil (Azadirachta indica) at 3 % emulsion at 7-day intervals
- apply Beauveria bassiana at 5 g/L
- release green lacewing larvae (Chrysoperla zastrowi) at 5,000/ha
- spray garlic-chilli-soap repellent (crushed garlic 100 g + chilli 50 g + soap 30 g in 10 L water)
- cut the crop early to disrupt the aphid population.
🧪 Chemical treatments
- Imidacloprid 17.8 SL @ 0.3 ml/L, Dimethoate 30 EC @ 1.5 ml/L, Pymetrozine 50 WG @ 0.5 g/L, Thiamethoxam 25 WG @ 0.4 g/L.
- Pre-harvest interval 7 days for imidacloprid, 14 days for dimethoate
- observe grazing interval — do not graze or cut for 14 days after dimethoate application.
🛡️ Prevention
- Conserve natural enemies — the single most important preventive measure, as the aphid's rapid reproduction is normally held in check by ladybirds, lacewings, and parasitic wasps
- cut the crop early when aphid populations exceed the economic threshold
- maintain balanced nitrogen nutrition — excessive nitrogen promotes soft, succulent growth highly attractive to aphids
- adopt a 2-year rotation with non-legume cereals
- plant resistant or tolerant lucerne varieties where available
- remove wild legume hosts around field margins.
🪴 Affected plants
- Lucerne (Medicago sativa, also called alfalfa) — primary host
- also infests pea (Pisum sativum), broad bean (Vicia faba), chickpea (Cicer arietinum), lentil (Lens culinaris), and many other legumes — over 200 recorded hosts across Fabaceae.
🦋 Natural predators
- Ladybirds (Coccinellidae — Coccinella septempunctata, Menochilus sexmaculatus, the most important aphid predators in lucerne)
- green lacewing larvae (Chrysoperla zastrowi)
- hoverfly larvae (Syrphidae)
- predatory midge larvae (Aphidoletes aphidimyza)
- aphid parasitoids (Aphidius ervi, A. smithi, Lysiphlebus — parasitise 20–40 % of aphids in unsprayed fields)
- and predatory bugs (Geocoris, Nabis).
🌱 Host plants
- Medicago sativa (lucerne/alfalfa — focus here)
- Pisum sativum (pea)
- Vicia faba (broad bean)
- Cicer arietinum (chickpea)
- Lens culinaris (lentil)
- and over 200 other legumes across Fabaceae.
🔄 Lifecycle
- In tropical India, reproduction is entirely parthenogenetic (anholocyclic) — females give birth to live female nymphs without mating.
- Each female produces 80–120 nymphs in her 25–30 day lifespan.
- Nymph passes through four instars over 8–10 days.
- Adult longevity 25–30 days.
- Total lifecycle (birth to reproduction) 8–10 days in summer, 14–18 days in winter.
- Winged forms (alatae) produced under crowding or host-quality decline.
- Twenty to thirty overlapping generations per year in tropical India.
📅 Season
- Active year-round in tropical India; peak populations during the cool season (November–March) and again in early spring (March–May) when temperatures are 20–25 °C.
- Population crashes during the hot dry summer (May–June) above 35 °C and during the heavy monsoon (July–September).
🔎 Appearance
- Adult is a medium-sized pear-shaped aphid (Aphididae) — colour variable from pale green to pinkish; legs and antennae are long relative to body size, distinguishing it from most other crop aphids; cornicles (siphunculi) are long and slender, about 1/3 the body length, slightly flared at the tip; cauda is long and finger-like.
- Nymphs are smaller versions of adults without wings.
- Winged forms (alatae) are produced when overcrowding or host-quality decline triggers dispersal.
💥 Damage level
- Moderate
🔁 Reproduction rate
- Fast
🗺️ Geographic regions
- Cosmopolitan in temperate
- subtropical
- and tropical regions worldwide — one of the most widely distributed agricultural aphids.
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