Development of an artificial host egg for in vitro egg laying of Trichogramma galloi and T-pretiosum using plastic membranes

An artificial host egg was developed as a first attempt to improve the tech niques for in vitro rearing of Trichogramma galloi Zucchi and T. pretiosum Riley (Hymenoptera, Trichogrammatidae). Plastic membranes (polyethylene, po lypropylene and polystyrene) of different thickness were tested for their u sefulness in manufacturing artificial eggs, using a thermal system to produ ce semi-spherical cupules on the plastic surface. These artificial eggs wer e filled with larval hemolymph of Helicoverpa zea (Boddie) (Lepidoptera, No ctuidae), and the optimal size of the artificial egg and density of females /artificial egg for the highest host acceptance (percentage of artificial e ggs with at least one parasitoid egg) as well as the ideal level of parasit ism (eggs/artificial egg) were determined. High-density polyethylene 7-8 an d 9-10 mu m thick resulted in the best acceptance and level of parasitizati on for both parasitoid species. Six females per artificial egg resulted in the best rate of parasitization for these parasitoids, although these data were not different when using 4 or 5 females of T. galloi. The size, shape and surface texture of the artificial eggs were found to provide enough cue s to elicit parasitization behavior in Trichogramma females, since no chemi cal stimulus was provided.