Diadegma (Eriborus) trochanteratus (Morley)

Diadegma (Eriborus) trochanteratus is a solitary, larval endoparasitoid attacking 4-7th instar larvae of the coconut caterpillar.

Mass culturing of the parasitoid is done by two methods, namely individual exposure method and mass exposure method, using Opisina larvae and for the alternative host, Corcyra cephalonica.

Fifth instar (30 day old) larvae of Corcyra or 4-7th instar larvae of Opisina are exposed individually to a mated female parasitoid held in a glass specimen tube (7.5 cm x 2.5 cm) inverted over a sheet of white paper. The parasitoid crawls over the larvae and quickly injects an egg into the body of the host with its ovipositor. Immediately after parasitisation regurgitation of a fluid sometimes follows. The larva is then removed and transferred into vials with appropriate food i.e., broken sorghum or pearl millet in the case of Corcyra and coconut leaf bits or artificial diet in the case of Opisina for further development. This method yields only 200-250 parasitised larvae per day by utilizing 6 hrs per man day.

In this method, host larvae of the same size or age as mentioned above are exposed "enmasse" at the rate of 10 larvae per mated female parasitoid for 3 hrs in a pneumatic glass trough of size 10x20 cm and covered with muslin cloth. The trough is kept on a sheet of paper in an inverted position to prevent the parasitoid from getting entangled in the webbing by the caterpillar. After a 3 hours exposure, the larvae are transferred to vials with food for development of the parasitoid.

After completing its development inside the host larva, the parasitoid larva transforms into a pupa constructing its cocoon inside the webbing already made by host larva (pre- pupal stage) before its death. The cocoons are found attached to the inner surface of the rearing containers or on the leaf or attached to the inner surface of the lid as the case may be. The cocoons are carefully removed on 10th day after parasitisation along with the webbing in the case of Opisina or separated from the grain in the case of Corcyra and kept in plastic or glass containers for emergence. (In any case no attempt should be made to remove the webbing which covers the cocoon).

Starting from 15th day after parasitisation the emerging adult parasitoids are collected daily normally in evening hrs. Equal numbers of males and females are held in glass vials or wooden cages 30 cm3. Next morning the females are separated for egg laying. Adult female live for about a week (2-15 days) and can parasitize about 120 larvae; the life cycle on Opisina takes about 16 days, egg 24-32 hrs, larva 5-8 days, pre-pupal 2-3 days and pupa 6- 8 days. But on Corcyra it is completed in 14-28 days. This method is five times more efficient and productive then individual exposure method.

The parasitoid can be multiplied on several hosts including Phthorimaea operculella Zeller, Dichocrocis punctiferalis (Guenee) and Helicoverpa armigera (Hübner).