Bracon kirkpatricki Wilkinson

Bracon kirkpatricki has been introduced from North Africa for evaluation against cotton bollworms. It has a wide host-range but it prefers larvae of pink bollworm Pectinophora gossypiella.

In the laboratory it can be bred on full grown larvae of Corcyra cephalonica (as in the case of Bracon breoicornis, with slight variations). In order to provide healthy host culture, 2 gm of yeast powder (5 tablets) and 0.5 gm of streptomycin sulphate are added for every 2.5 kg of ground sorghum or pearl millet on which the C. cephalonica larvae are fed. The yeast and streptomycin are thoroughly mixed with the crushed grains.

Twenty mated females are confined in a glass chimney by covering both the openings with square pieces of muslin held in place by rubber bands. A cotton swab soaked in a solution of l gm 'protinex' in 20 ml distilled water with the contents of one vitamin E capsule (Viteolin) is stuck to the inside of the chimney to serve as food. No honey is necessary, because substituting honey with 'protinex' and vitamin E provides a better sex ratio. Ten full grown C.cephalonica larvae are placed between two sheets of facial tissue and placed over the muslin sheet covering the wider end of the chimney. The tissue is again covered by a piece of muslin held in place by rubber bands.

One day old adults are be allowed to mate by keeping males and females together for 24 hrs. After mating the females are kept separately and held for 24 hours before being exposed to host larvae.

The female parasitoids can sense the movement of C. cephalonica larvae beneath them as they tap the muslin cloth with their antennae. As soon as a suitable host is located the female probes through the muslin cloth and facial tissue paper with the ovipositor, injects an immobilizing venom and begins to lay eggs on the host larva. The hosts are exposed for 24 hrs daily. Approximately 60 to 90 eggs are laid on ten larvae every day. These hatch within 48 hours and begin to feed externally. Total developmental period is about 10 to 11 days. The adults can survive up to 25 days, but progeny production declines after 10 days.

After exposure to female parasitoids, the parasitized larvae are held in the same tissue paper, until the fully fed parasitoid larvae drop off from the host, spin silken cocoons, pupate, and finally emerge through the tissue as adults.Temperature in the rearing room should preferably be maintained at 27°C (50% RH) and the number of day light hours should be adjusted to at least 10.In nature, B. kirkpatricki females attack the bollworm larvae when they are present on the blooms.An improved mass-rearing technique could be adopted in which 1500-1600 of the parasitoids are released in a large flat transparent plastic container covered with organdy or muslin. A 20 gram capacity screw top vial containing a 10% solution of laevulose and water fitted the sponge wick serve as a source of food. These vials are changed twice a week.The cage is placed over a flat plastic sheet, over which is placed a layer of paper toweling bearing about 70 host larvae covered with a layer of thin paper toweling.

Adults parasitoids are exposed to the hosts for 30 minutes to 2 hours (depending on the age of the females), after which the cage is removed. The sheets of paper toweling bearing hosts are stacked in batches of 20 with a piece of wire mesh separating every fourth assembly. After cocoon formation takes place, the sheets are removed and hung vertically in eight darkened chambers fitted on top with inverted plastic funnels. These emergence chambers made of wood and comprising of eight compartments are fitted with nine rods arranged in three tiers from which the sheets of toweling bearing parasitoid cocoons are hung.

Fluorescent lights are hung over the emergence boxes so that the phototropic parasitoids move directly into fresh parasitisation cages or field-release boxes . The latter are just cardboard boxes (37.5 cms x 30 cms x 25 cms), modified by replacing one end with organdy on muslin and placing vials for feeding with laevulose solution. Each could hold 20,000 to 30,000 adult parasitoids.

The adoption of this method for breeding could greatly increase rearing efficiency. Egg + larval, pupal periods and adult longevity is 51.1± 0.0, 5.7± 0.5 and 28.6 ±5. 7 days. Each female parasitises 30.0±11.8 hosts, lay 36.8±10.5 eggs, producing 31.4±5.8 adults.

Cocoons of B. kirkpatricki could be stored for 20 days at 6.5 °C