Cannibalistic feeding of larval Trichogramma carverae parasitoids in moth eggs

Wasps of the genus Trichogramma parasitise the eggs of Lepidoptera. They may deposit one or many eggs in each host. Survival is high at low density but reaches a plateau as density increases. To reveal the mechanism by which excess larvae die we chose a lepidopteran host that has flattened, transparent eggs and used video microscopy to record novel feeding behaviours and interactions of larval Trichogramma carverae (Oatman and Pinto) at different densities. Single larvae show a rapid food ingestion phase, followed by a period of extensive saliva release. Ultimately the host egg is completely consumed. The larva then extracts excess moisture from the egg, providing a dry environment for pupation. When multiple larvae are present, the initial scramble for food results in the larvae consuming all of the egg contents early in development. All larvae survive if there is sufficient food for all to reach a threshold developmental stage. If not, physical proximity results in attack and consumption of others, continuing until the surviving larvae reach the threshold stage beyond which attacks seem to be no longer effective. The number of larvae remaining at the end of rapid ingestion dictates how many will survive to emerge as adults.

Egg parasitoids of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), from south-east Queensland

Field surveys of egg parasitoids of the diamondback moth, Plutella xylostella, were conducted at Redlands and Gatton, south-east Queensland. Eggs of P. xylostella were present all year round in both localities, and parasitized eggs were consistently found between late spring and early winter. Percent parasitism in the range 30-75% was recorded on many occasions, although rates less than 10% were more common. The major parasitoids included Trichogrammatoidea bactrae Nagaraja and Trichogramma pretiosum Riley. Laboratory evaluation showed that the T. pretiosum from Gatton has a high capacity to parasitize P. xylostella eggs under suitable conditions. This study represents the first record of egg parasitoids of P. xylostella from Australia.

Effects of temperature, salinity, desiccation and chemical treatments on egg embryonation and hatching success of Benedenia seriolae (Monogenea : Capsalidae), a parasite of farmed Seriola spp.

The effects of temperature and salinity on the embryonation period and hatching success of eggs of Benedenia seriolae were investigated. Temperature strongly influenced embryonation period; eggs first hatched 5 days after laying at 28 degreesC and 16 days after laying at 14 degreesC. The relationship between temperature and embryonation period is described by quadratic regression equations for time to first and last hatching. Hatching success was >70% for B. seriolae eggs incubated at temperatures from 14 to 28 degreesC. However, no B. seriolae eggs embryonated and hatched at 30 degreesC and

The effect of parasitization by Trichogramma australicum on Helicoverpa armigera host eggs and embryos

Histological investigations of the pathology of Helicoverpa armigera (Hiibner) eggs after attack by the egg parasitoid, Trichogramma australicum (Girault), indicate that the developing embryo is immediately killed by envenomation. Soon afterward the histological staining characteristics of parasitized host embryos change and the embryonic germ band dissociates into a mass of individual rounded cells. Hosts attacked by females sterilized by gamma-irradiation showed the same pathological effects as normally parasitized hosts, indicating that host degeneration is due to female venom rather than factors derived from the parasitoid embryo or larva. Cell death also occurred in older host embryos although tissue breakdown was delayed. These findings have allowed us to determine not just that the host dies but what happens to the cells and tissues, i.e., their physical appearance, the time course of their degeneration, and that the process is retarded in older hosts. These processes can possibly be emulated in artificial diets. (C) 2003 Elsevier Inc. All rights reserved.