Sara Kehail, Hayder Abdelgader, Olaf Zimmermann:
Host Parasitisation, Adult Emergence Rate and Female Ratio of the Egg Parasitoid Trichogramma piceum Dyurich (Hymenoptera, Trichogrammatidae) as affected by Holding Temperature

SARA KEHAIL¹, HAYDER ABDELGADER¹, OLAF ZIMMERMANN^2
1Agricultural Research Corporation, Crop Protection Research Center, Sudan
²JKI Institute for Biological Control, Beneficial Group, Germany

Trichogramma piceum adults (Hymenoptera, Trichogrammatidae) are extremely tiny wasps. Their females seek out and parasitize host eggs of noxious lepidopterous insect pests such as Helicoverpa armigera. The recent study aimed at measuring the egg parasitism, emergence rate and female ratio at different periods and different holding temperatures, with the objective to evaluate the efficiency of using this beneficial to combat infestation of the boll worm both on edible and non-edible crops in Sudan and other countries with similar environmental conditions. The experiments were conducted in two separate temperatures (25°C and 30°C) at the same time, where Helicoverpa armigera egg"=card was exposed to 24 hours old female of T. piceum. New egg cards were exchanged daily until tested females died. The results showed a strong exponential relationship (R² > 0.8) at both temperatures tested between egg parasitism and age of the tested adult parasitoid. More than 50% of the parasitoid eggs were laid in the first 4 days or 2 days after introducing the adult parasitoids with a parasitism rate of 4.1 or 4.6 black eggs /female parasitoid/day at 25°C or 30°C, respectively. The adults survived for ca. 10 days or 5 days depending on holding temperature. Regardless of the temperatures no difference was observed between the emergence rate and the period of parasitism (ranging 1.1 and 1.3) for the tested periods for both tested temperatures. A highly significant negative linear relationship (R² was 0.92 or 0.80 for 25°C or 30°C respectively) was observed between period of parasitism and female ratio. The ratio was 78% or 86% at the first 4 days or 2 days for T. piceum egg"=laying at 25°C or 30°C respectively. A drop in female ratio was observed afterwards.

Keywords: Ermergence rate, parasitism, sex ratio, temperature, Trichogramma piceum

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Contact Address: Sara Kehail, Agricultural Research Corporation, Crop Protection Research Centre, Entomology SectionWad Medani, Sudan, e-mail: saraagricyahoo.com