Biological Control of Mealybug in Custard Apple Using Verticillium lecanii

The Mealybug Threat to Custard Apple Cultivation

Mealybugs (Planococcus spp., Phenacoccus spp.) have emerged as a severe pest in custard apple (sugar apple, Annona squamosa) orchards worldwide. These soft-bodied, sap-sucking insects cluster on tender shoots, leaves, flower buds, and developing fruits, causing:

• Direct damage: Stunted growth, leaf yellowing, sooty mold growth on honeydew, and fruit deformation.

• Economic loss: Reduced fruit quality, premature fruit drop, and yield losses of 30-50% in severe infestations.

• Management challenges: Their waxy coating and hidden habitats make chemical control difficult and environmentally hazardous.

Verticillium lecanii: The Fungal Biopesticide

Verticillium lecanii (now often classified under Lecanicillium lecanii) is an entomopathogenic fungus that offers a safe, effective, and eco-friendly solution. It acts as a parasitic fungus that specifically targets soft-bodied insects like mealybugs, aphids, and whiteflies.

Mode of Action

1. Contact and Infection: Fungal spores (conidia) come into contact with the mealybug's cuticle under favorable humidity.

2. Germination and Penetration: The spores germinate, and hyphae physically penetrate the insect's exoskeleton using enzymatic action.

3. Colonization: The fungus grows inside the host body, consuming its nutrients.

4. Symptom & Death: Infected mealybugs become lethargic, change color (often turning pink or brown), and become mummified. Within 3-7 days, white fungal mycelium emerges from the dead insect, producing new spores that spread the infection to other pests.

Advantages for Custard Apple Cultivation

• Target-Specific: Harmless to pollinators (bees), beneficial insects, birds, and mammals.

• No Residue: Ideal for organic production and export-quality fruit.

• Resistance Management: Does not contribute to pesticide resistance.

• Soil & Plant Health: No adverse impact on soil microbiota or plant physiology.

Practical Application Protocol

1. Product Selection

• Choose a commercial formulation of V. lecanii with a high spore count (minimum 1 x 10⁸ CFU/g).

• Available as Wettable Powder (WP) or Oil-based Suspension for better adhesion.

2. Optimal Conditions for Application

• Time: Apply during early morning or late afternoon for high humidity.

• Weather: Avoid application under strong sunlight or during heavy rain. Optimal temperature: 20-28°C.

• Stage: Initiate sprays at the first sign of mealybug colonies (usually on undersides of leaves or fruit pedicels).

3. Preparation of Spray Solution

• Dosage: Use 5-10 grams of V. lecanii WP per liter of water.

• Mixing: First, make a slurry with a small amount of water, then dilute to full volume.

• Additives: Add a sticker-spreader (e.g., mild soap, neem oil at 0.5%) to enhance adhesion on the waxy insect bodies.

• Water Quality: Use chlorine-free water at neutral pH.

4. Spray Method

• Use a fine mist sprayer for thorough coverage.

• Focus Areas: Drench undersides of leaves, leaf axils, tender shoots, flower buds, and fruit surfaces.

• Volume: Ensure complete canopy coverage (typically 500-800 liters per hectare).

5. Spray Schedule

• First Spray: At initial pest detection.

• Follow-up: Repeat at 7-10 day intervals for 2-3 cycles, or as needed.

• Preventive Spray: Can be included in regular integrated pest management (IPM) schedules during flowering and fruit-set stages.

Integrated Pest Management (IPM) Strategy

V. lecanii is most effective when combined with other biocontrol practices:

1. Cultural Controls:

   • Prune and destroy heavily infested shoots.

   • Maintain orchard sanitation to remove ant colonies (which protect mealybugs).

   • Use balanced fertilization to avoid excessive succulent growth that attracts pests.

2. Support with Other Biocontrol Agents:

   • Predators: Release Cryptolaemus montrouzieri (mealybug ladybird) larvae.

   • Parasitoids: Conserve native parasitoid wasps (Anagyrus spp.).

   • Combine with Beauveria bassiana (another entomopathogenic fungus) for broader spectrum control.

3. Botanical Support:

   • Alternate or tank-mix with neem-based insecticides (azadirachtin) which disrupt insect growth and synergize with fungal pathogens.

4. Monitoring:

   • Use yellow sticky traps to monitor flying adult males.

   • Conduct weekly orchard scouting, especially during flowering and fruit development.

Do's and Don'ts

✅ DO:

• Apply under high humidity conditions (>80% RH).

• Ensure thorough spray coverage on hidden pest niches.

• Store the product in a cool, dry place away from sunlight.

• Wear protective mask during spraying to avoid spore inhalation.

❌ DON'T:

• Do not mix with chemical fungicides or broad-spectrum insecticides.

• Do not apply under dry, hot conditions (temperature >35°C).

• Do not use chlorinated water for spore suspension.

• Do not combine with sulfur-based compounds.

Expected Results & Economic Benefit

With consistent application, farmers can expect:

• 70-80% reduction in mealybug population within 2-3 spray cycles.

• Healthier fruit set and reduced sooty mold incidence.

• Significant reduction in chemical pesticide costs.

• Compliance with organic certification standards and access to premium markets.

Conclusion

Verticillium lecanii represents a powerful, sustainable tool in the management of mealybugs in custard apple. By integrating this fungal biopesticide into a holistic IPM program, growers can protect their yields, enhance fruit quality, and promote long-term orchard health—aligning productivity with ecological responsibility. For region-specific advice, consult your local agricultural university or horticulture department. 

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