WHITEGRUB IN GROUNDNUT: Pest Overview, Life cycle, Symptoms and Management

1. Pest Overview

Scientific Classification:

• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta
• Order: Coleoptera
• Family: Scarabaeidae
• Commonly Affected Species: Holotrichia consanguinea, Holotrichia serrata, Anomala dimidiata

Common Names: White grub, root grub, beetle larva.

Morphology and Identification:

• Larvae (Grubs): C-shaped, creamy-white body with a brown head capsule. They have three pairs of thoracic legs and a soft, fleshy abdomen. Larval length ranges from 1–4 cm depending on instar stage.
• Adults (Beetles): Robust, brownish to black beetles, 1–2 cm long. Active mainly at night; they feed on foliage lightly but their major damage is through oviposition in soil and root-feeding larvae.
• Life Cycle Stages: Egg → Larva (3–4 instars) → Pupa → Adult.

Biology and Life Cycle:

• Female beetles lay eggs 1–2 inches deep in soil, usually in loose, moist areas rich in organic matter.
• Larval Stage: Lasts 1–3 years depending on species and climate, during which grubs feed on roots, reducing water and nutrient uptake.
• Pupation: Occurs in earthen cells created in the soil. Duration varies with temperature and moisture.
• Adult Emergence: Adults typically emerge with the onset of monsoon rains, mate, and lay eggs, continuing the infestation cycle.
• Reproduction & Population Dynamics: One female can lay 40–60 eggs; populations build rapidly in monoculture fields with susceptible crops.

Seasonal Occurrence:

• Adults appear primarily during rainy season (June–September in India).
• Larval activity peaks during post-monsoon to pre-summer, causing maximum damage to roots of young seedlings.

2. Host Range

Primary Host:

• Groundnut (Arachis hypogaea)

Secondary Hosts:

• Cereals: Maize, sorghum, wheat, rice
• Sugarcane and other grasses
• Vegetables: Tomato, brinjal, potato (occasionally)

Crops Commonly Affected by Region:

• Southern India (Karnataka, Tamil Nadu, Andhra Pradesh) and central India (Madhya Pradesh, Maharashtra) report high infestations.
• Infestations are more severe in red and black cotton soils and in fields with heavy organic matter accumulation.

3. Symptoms & Identification

Visible Damage Symptoms:

• Seedlings may fail to emerge (pre-emergence damping-off).
• Young plants exhibit wilting, yellowing, and stunted growth.
• Mature plants have reduced pod formation and uneven maturation.
• Roots exhibit tunnels, gnaw marks, and decay.

Signs of Infestation:

• Uprooting reveals C-shaped creamy larvae.
• Presence of adults on field edges at night.
• Patchy wilting in irregular clusters.

Distinguishing White Grub Damage from Other Soil Pests:

• Unlike termites, which chew stems at soil surface, white grubs feed mainly on roots below ground.
• C-shaped, thick-bodied larvae distinguish them from straight-bodied root maggots or cutworms.
• Damage to taproot and lateral roots reduces water and nutrient uptake more severely than surface feeders.

4. Economic Impact

• Yield Loss: Heavy infestations can reduce yield by 20–50% depending on population density and crop stage.
• Quality Loss: Stunted plants produce fewer pods; roots may rot and predispose plants to secondary soil-borne pathogens.
• Financial Implications: Input costs (seed, fertilizer) are wasted in heavily infested fields. Untreated infestations may cause significant revenue loss for farmers.

Example: In Karnataka, surveys report 25–40% yield reduction in groundnut in heavily infested fields without timely intervention.

5. Integrated Pest Management (IPM) Practices

A. Cultural Practices

• Crop Rotation: Rotate groundnut with cereals or other non-host crops to reduce grub populations.
• Deep Plowing: Exposes grubs to sun and predators. Plow fields 3–4 weeks before sowing.
• Field Sanitation: Remove weeds, crop residues, and decaying roots that serve as larval food.
• Optimal Planting Time: Avoid sowing immediately after monsoon in fields known for adult beetle activity.

B. Biological Control

• Entomopathogenic Fungi: Beauveria bassiana, Metarhizium anisopliae effectively infect and kill grubs.
• Entomopathogenic Nematodes: Heterorhabditis and Steinernema spp.
• Predators: Encourage birds, ants, and predatory beetles.
• Application: Introduce bio-agents to moist soil during peak larval activity for maximum effect.

C. Chemical Control

• Granular Insecticides: Chlorantraniliprole 0.4–0.5 kg/ha, applied in furrows at sowing.
• Seed Treatment: Imidacloprid or thiamethoxam-treated seeds reduce early larval attack.
• Timing: Pre-sowing or early post-emergence for maximum efficiency.
• Spot Treatment: Targeted application in highly infested patches reduces chemical load and cost.

D. Preventive Measures & Monitoring

• Soil Inspection: Regularly inspect for larvae 10–15 days after sowing.
• Light Traps: Capture adults to monitor population build-up.
• Avoid Continuous Monocropping: Alternate with non-host crops to naturally reduce population.

6. Agribusiness Relevance

• Seed Companies: Promote resistant or tolerant varieties; provide treated seeds.
• Fertilizer Companies: Recommend balanced fertilization to enhance root growth, reducing susceptibility.
• Pesticide Companies: Introduce efficient, safe, and cost-effective bio-pesticides and chemical solutions.
• Farmer Advisory Services: Educate farmers on early detection, monitoring, and IPM adoption to maximize yields.