none Aphidius ervi; EGG-LAYING; Oviposition, recognition & acceptance behaviour; HEMIPTERAN-HOSTS; Acyrthosiphon pisum; Host recognition & acceptance behaviour, role of physical cues & kairomones Acyrthosiphon pisum; CHEMICAL-SIGNALS; Kairomones, role in parasitism by Hymenoptera; HYMENOPTERAN-PARASITES; Aphidius ervi; Host recognition & acceptance behaviour, role of physical cues & kairomones The role of color and shape in the host recognition and acceptance behavior of Aphidius ervi Haliday was studied. A quantitative analysis of the oviposition behavior of A. ervi was carried out with a computer-aided analysis of 150 video-recorded oviposition sequences on its natural host, Acyrthosiphon pisum (Harris). The importance of visual stimuli was assessed in a choice condition bioassay, observing the behavioral reaction of female parasitoids to various test materials flame-sealed into glass capillaries. Glass beads 2 and 6 mm in diameter and a flat arena were coated with cornicle secretion of A. pisum, and their acceptance rates by both naive and experienced female parasitoids were assessed under no-choice conditions. In most cases, A. ervi females switched from random searching to attack position when the host was within a range of 1 cm, suggesting that host recognition is regulated in part by cues acting before physical contact. The glass capillary bioassay indicated that visual cues are important factors in the host recognition and acceptance phases. Pea aphid color alone can elicit the oviposition response of naive A. ervi females, and this response is enhanced when color is combined with aphid shape. The cornicle secretion of A. pisum stimulated an oviposition response which was stronger in naive females of A. ervi than in experienced ones and was not significantly affected by the glass bead size or flat surface. These results, along with those from previous studies, suggest that manipulation of the oviposition behavior of A. ervi is feasible under laboratory conditions.