Some Important Insect Parasitoids
Trichogramma spp. Are true egg parasitoids widely distributed in insect. The taxonomy of the various species is difficult, but it is now been classified that over 200 insects species belonging to 70 families and 8 orders in diverse habits are parasitized by species, subspecies and various strains of Trichogramma. Out of 26 Trichogramma species recorded in India T. japonicum and T. achea are widely distributed and are key factors for many crops pest in India. These parasitoids are mostly used against pests like sugarcane borer (Chilo spp), paddy stem borer, tomato fruit borer, cutworms, cotton bollworms etc.
A female lays about 1 to 20 eggs in one host egg depending on size of eggs but in the eggs of sugarcane bores only 1-2 eggs of Trichogramma are posited per egg. Its fecuandity varies from 20 to 200 eggs according to species and longevity of adults. Incubation period of eggs lasts for a day (16 to 24 hours). Larval period is 2-3 days, prepupal and pupal periods varies 2-3 days, and total life cycle is completed in 8 – 10 days during summer and 9 – 12 days during winter. Host eggs become dark in 3 -4 days after the parasitilization because of accumulation of urate granules unorganized eggs remain 1:1 ( M: F ). Host searching capacity is up to 3-5 meters in filed. Rice moth, coryra cephalonica is used as facitituous host for multiplication of Trichogramma in laboratory.
2. Bracon brevicornis:
It is a potent larval parasitoids of coconut black headed caterpillar. The parasitoid is an external gregarious, larval parasitoid and lays about 6 to 2 eggs pr host larvae. Its egg stage lasts for 24 to 48 hrs larval stage 5 – 6 day and pupal stage 4 to 6 days. A life cycle of the parasitoids is completed within 15 days. The pupae of the parasitoids are silvery cocoons can be stored for 10 – 15 days in refrigeration. In laboratory, the parasitoids are reared on larvae of rice moth, Corcyra cephalonica, and the adult parasitoids of Bracan brevicornis are used for releasing them in coconut plantation against target pests. Release of 40,000 to 50,000 and per r hectares week and follow such 4- 6 releases are recommended in fields.