PARASITISM, SURVIVORSHIP, SEX RATIO AND DEVELOPMENTAL TIME OF COTESIA MARGINIVENTRIS (CRESSON) (HYMENOPTERA: BRACONIDAE), PARASITIZING RACHIPLUSIA NU (GUENNÉE) (LEPIDOPTERA: NOCTUIDAE) LARVAE IN SOYBEAN CROPS IN ARGENTINA

Résumé

Cotesia marginiventris (Cresson) (Hymenoptera: Braconidae), is one of the most important parasitoid
species of the natural enemy complex atacking Rachiplusia nu (Guenée) (Lepidoptera: Noctuidae) in soybean
crops in Buenos Aires Province, Argentina. The objective of this study was to analyze the parasitism,
survivorship, sex ratio and developmental time of C. marginiventris. Two R. nu generations were sampled in
crops in Buenos Aires Province during the growing seasons of 1992 and 1993, and only one in 1994.
Percentage parasitism was: 32.3% and 20% in 1992; 32.6% and 40% in 1993; and 43.9% in 1994. Cumulative
percentage parasitism for the first and second generation was:21%and 19,3% in 1992; 13.7% and 35.7% in
1993; and 24.4% the only generation in 1994. Parasitoid mortality affected mainly the pupal stage. Sex (male:
female) ratio was (1:1.5). Mean developmental time from host collection (larvae < 1.5 cm length) to adult
parasitoid emergence was 7.89 +- 2.26 days (27 +- 1°C; 70% HR; 16:8 L:D).