Varying infestation of alfalfa by the seed chalcid,Bruchophagus roddiGussakovsky, is explained by antixenosis during oviposition. Our studies suggest that alfalfas with glandular-haired and tightly coiled pods are resistant. Oviposition resulted in seed damage even when larvae did not develop. Seed abortion was 33% in seed chalcid exposed and 16% in unexposed seed pods. The black or brown marks left on developing seeds by ovipositing females may be used in designing laboratory experiments to predict resistance in the field.