none Cotesia glomerata; AGE-; Pupal, effect on Eurytoma parasitization rate; PUPAL-DEVELOPMENT; Pupal age effect on Eurytoma parasitization rate; HYMENOPTERAN-PARASITES; Eurytoma; Host age & cocoon position effects on parasitization rate; COCOONS-; Cocoon position effect on Eurytoma parasitization rate; JAPAN-; Honshu, Okayama; Pupal age & cocoon position effects on Eurytoma parasitization rate Eurytoma; EGG-LAYING; Oviposition rate, effects of Cotesia host age & cocoon position; HYMENOPTERAN-HOSTS; Cotesia glomerata; Host age & cocoon position effects on parasitization rate; POPULATION-SEX-RATIO; Progeny sex ratio, effect of Cotesia host age, Japan. Host age preference of the hyperparasitoid, Eurytoma sp., attacking the cocoons of the gregarious parasitoid wasp, Cotesia (= apanteles ) glomerata L., was investigated in the field and laboratory. Under laboratory conditions of 20 degree C and L16D8 photoperiod, Eurytoma sp. parasitized cocoons of all ages, laying 7 to 10 eggs per cluster during a 24 h period. Field-collected cocoons also indicated that the host was parasitized regardless of its developmental stage. However, the mortality of Eurytoma sp. laid in cocoons on the day before host emergence was as high as 60%. Furthermore, progeny sex ratio (proportion males) reached 0.708 in eggs laid in the oldest cocoon clusters, whereas that for younger cocoons was strongly female-biased. Together, these facts suggest that older hosts are less suitable for Eurytoma sp. than are younger ones, even though there was no significant decreasing tendency in the number of parasitized cocoons per cluster. In addition, the effect of cocoon position within a cluster was apparent, outer cocoons being more easily parasitized than inner ones. The Eurytoma sp. female oviposited at random on the free surface of C. glomerata cocoons.