Biological characteristics:: growth and development of the egg parasitoid Trichogramma dendrolimi (Hymenoptera: Trichogrammatidae) on the cabbage armyworm Mamestra brassicae (Lepidoptera: Noctuidae)

The growth and development of Trichogramma dendrolimi in the host, Mamestra brassicae, egg was morphologically observed. T. dendrolimi grew rapidly to full size by 2 d after parasitism, sucking up nearly all of the host yolk as the food resource. Thereafter, they did not increase in size. The parasitoid became a first larval instar on day 1, prepupa on day 4, and pupa on day 5 after parasitization. Emergence of adult wasps from the host egg occurred 9 d after parasitization. A well developed ovary was observed 8 d after parasitization, suggesting that the wasp can oviposit immediately after emergence. To clarify host stage suitability for successful parasitism, 1 to 4.2 d old eggs of M. brassicae were offered to female wasps. T. dendrolimi was able to parasitize M. brassicae eggs of all ages. The parasitoid wasp appears to arrest the development of the host by a venom. However, successful parasitism significantly decreased on 4 d and 4.2 d old host eggs. The female ratio of the progeny decreased with the aging of the female wasps, but neither the sequential change of the host age nor variation of the host egg mass size affected the female ratio of the progeny, which was about 80%.