Host Egg Age and Supplementary Diet Influence the Parasitism Activity of Trichogramma zahiri (Hymenoptera: Trichogrammatidae).
Mass production of egg parasitoids mostly depends on the age of the host. Generally old eggs are less preferred by egg parasitoids, which can discriminate between eggs of different ages by using chemical cues. This study was designed to determine the preference, development, and arrestment of Trichogramma zahiri Polaszek (Hymenoptera: Trichogrammatidae) parasitizing eggs of its native host, the rice hispa, Dicladispa armigera (Olivier) (Coleoptera: Chrysomelidae). Eggs of different ages, in addition, with or without supplementary foods were evaluated. T. zahiri preferred to parasitize 1-d-old eggs rather than 2-, or 3-d-old eggs by no-choice assays. However, although the percentage emergence of parasitoids is significantly lower from 2- and 3-d-old eggs, the sex ratio is unaffected. Parasitoids lived longer when 25% honey solution was provided with the host food. Significantly higher fecundity (38.5 eggs per female) and parasitoid emergence (94.6%) occurred when 25% honey solution was provided in the diet with host food, followed by 25% sugar solution, as compared to the control (only water as food). An average of 7.9 eggs were parasitized when one parasitoid was released per 10 rice hispa eggs. Ability of T. zahiri to parasitize egg increased with an increase in the number of eggs offered. We also found that inclusion of a fresh host egg with the supplementary diet improves the mass rearing of T. zahiri for commercial purposes.
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T. zahiri; density dependent; diet; fecundity; host age preference