STEINBERG, S., Department of Entomology, The Hebrew University, Israel
PODOLER, H., Department of Entomology, The Hebrew University, Israel
ROSEN, D., Department of Entomology, The Hebrew University, Israel

ABSTRACT. 1. During the last decade, the endoparasitic wasp Pteroptrix smithi (Compere) has gradually replaced the ectoparasitic wasp Aphytis holoxanthus DeBach on the Florida red scale, Chrysomphalus aonidum (L.), on citrus in Israel. The studies reported herein were aimed at elucidating some of the mechanisms of this process. 2. Aphytis adults detected, and were attracted to hosts containing eggs of Pteroptrix, whereas adults of Pteroptrix did not detect hosts containing eggs of Aphytis. In this extrinsic aspect of host discrimination, Aphytis is superior to its competitor. Neither species responded to hosts containing heterospecific first‐instar larvae, and both tended to avoid hosts containing more advanced developmental stages of the other species. 3. Aphytis outcompeted Pteroptrix in most cases of multiple parasitism, as observed under both controlled and field conditions. 4. Aphytis was superior in mixed‐species cultures; however, its dominance was affected by the availability of adult food. 5. Aphytis adults were found to be more sensitive (×4.11) to the insecticide malathion as compared to adults of Pteroptrix. This finding provides a possible explanation to the displacement of Aphytis by Pteroptrix in the citrus groves along the coastal plain of Israel. Copyright © 1987, Wiley Blackwell. All rights reserved