Mass multiplication and field release techniques of some important parasitoids

1. Trichogramma chilonis (Family – Trichogrammatidae, Order – Hymenoptera)

chilonis is one of the most potent egg parasitoids for various Lepidopteran pests, such as bollworms and stem borers.

Materials:

• Egg Cards (Trichocards): 17.5 x 14 cm with 17 x 10 cm space for gluing eggs, and 5 x 1.75 cm pre-punched segments.
• Host Eggs: Corcyra cephalonica eggs, gum Arabic, camel hair brush, cotton swab, cotton wool, test tubes, honey.
• Containers: Glass or plastic jars, polythene bags, muslin cloth, rubber bands, scissors, clips.
• UV Chamber: Fluorescent tube light (40W), working tables.

Mass Rearing Methods:

• Preparation of Host Eggs: Corcyra eggs are separated from dust and scales using sieves (15, 30, and 40 mesh). The eggs are measured with a cylinder to quantify them. Expose these eggs to UV light (30W UV tube) for 45 minutes at a 2-feet distance to prevent premature hatching.
• Setting Up Trichocards: Information like species name, release date, manufacturing institute, etc., is written on the backside of Trichocards. Smear the upper side (punched side) of the cards with a thin layer of gum Arabic using a camel hair brush. Host eggs (Corcyra) are sprinkled onto the gum-coated surface, allowing them to dry.
• Parasitoid Introduction: Place the egg cards in a container (plastic bowl, glass tube, or polythene bags) and expose them to female T. chilonis for 24 hours. Maintain a ratio of 1 parasitoid to 6 unparasitized eggs for optimal parasitization. After parasitization, larvae that hatch from non-parasitized eggs should be removed to prevent them from destroying parasitized eggs. Parasitized eggs change color from creamy white to black within 4 days due to the accumulation of urate granules.

Storage: Parasitized eggs can be stored for about 30–35 days at 10°C in a refrigerator.

Field Release: Release parasitoids in their pharate stage (when a few adults begin emerging) during the evening. Cut the Trichocard into pieces and staple them beneath foliage in the upper canopy. The parasitoid: host ratio should be about 1:6. To maximize effectiveness, release in as many locations as possible. For large-scale releases, 1 card per 5 meters of row length is recommended.

Precautions: Maintain quality by monitoring egg parasitization rates (95% ± 5%) and adult emergence (90% ± 5%). Genetic deterioration can occur with repeated mass rearing, so it’s essential to rejuvenate genetic stock periodically by introducing natural hosts.

2. Chelonus blackburni (Family – Braconidae, Hymenoptera) Chelonus blackburni is a parasitic wasp that is effective against pests like the cotton bollworm and potato tuber moth.

Materials:

• Rearing Units: Wooden boxes, crushed sorghum grains, egg cards, gum Arabic, Corcyra eggs.
• Breeding Units: Muslin cloth, rubber bands, scissors, wide-mouth plastic jars.
• Host: Rice moth (Corcyra cephalonica), Potato Tuber Moth (PTM).

Mass Rearing Methods:

1. Rearing on Corcyra Eggs: Use 100, 0-24 hour old Corcyra eggs (not exposed to UV) pasted onto a 5×5 cm card. Expose the cards to C. blackburni adults for 24 hours in a plastic container with aeration windows (plastic mesh). Place cotton swabs soaked in 10% honey solution for feeding.
2. Development: After exposure, the cards are removed and placed on a sterilized cumbu medium (500g). In about 30 days, adults emerge from the cocoons formed in the medium after completing development on the Corcyra larvae.
3. Rearing on Potato Tubers: Set 1500 eggs on a cloth and staple them onto a card. Expose this to C. blackburni adults. The card is then placed on punctured potatoes, which allow larvae entry points. Adults emerge after 25–27 days from cocoons formed inside the sand or potatoes.

Field Release:

• For cotton: Release 60,000 adults per hectare per week, over 4 releases, starting 60 days after planting.
• For stored potatoes: Release 2 adults per kg of tubers.

3. Cotesia / Bracon (Family – Braconidae, Hymenoptera)

brevicornis is a gregarious larval ecto-parasitoid, which targets various lepidopteran pests such as Helicoverpa armigera and Chilo partellus.

Production Procedure:

1. Host and Rearing: B. brevicornis is mass-reared on Corcyra cephalonica larvae. Set up a glass chimney with muslin sheets on both sides, providing aeration and a cotton swab soaked in a 50% honey solution for nutrition.
2. Parasitoid Life Cycle: Place 10 full-grown Corcyra larvae between two tissue sheets and place them inside the chimney. B. brevicornis females parasitize the larvae, laying about 25 eggs per day. After 24 hours, remove the tissue and place it in a flat container until parasitoid larvae hatch and pupate in cocoons.
3. Adult Collection: Adults emerge after 15-40 days and lay 150-200 eggs in their lifetime. For effective mass rearing, replace host larvae regularly.
4. Goniozus nephantidis (Family – Bethylidae, Hymenoptera)
5. Goniozus nephantidis is a parasitic wasp that targets the sugarcane borer pest Scirpophaga excerptalis.

Methods for Mass Rearing and Field Release:

1. Mass Rearing: Use Nephantis as the host for rearing. Eggs are glued onto a card and exposed to adult parasitoids. After parasitization, the parasitized larvae are placed in containers to allow the parasitoids to complete their development.
2. Field Release: Release the parasitoid in the field at the peak of pest infestation for best results. A release rate of 50,000 parasitoids per hectare is recommended.