Comparison of different European strains of Trichogramma aurosum (Hymenoptera: Trichogrammatidae) using fertility life tables

Life table parameters were assessed for seven strains of Trichogramma aurosum Sugonjaev and Sorokina (Hymenoptera: Trichogrammatidae) collected in different European countries, in order to compare their performance when reared on eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) as a potential factitious host for mass-rearing. The average number of progeny per female, cumulative fertility and emergence rate did not differ significantly, whereas female longevity and sex ratio significantly differed between the seven parasitoid strains. The Danish strain survived the longest (6.05 days) and the Dutch strain survived the shortest (2.75 days). Progeny was always female-biased with varying proportions (57.7-96.7%). Survival rates started to decrease after 3 days for some of the strains studied. The mean cohort generation duration (T_c) was 11.40, 10.15, 10.62, 10.63, 9.28, 9.70 and 11.30 days for the Austrian, Luxemburgian, Belgian, French, Dutch, Danish and German strains, respectively. Population doubling time (D_t) was 4.50, 7.96, 3.56, 5.30, 5.23, 7.36 and 3.30 days, respectively. Daily intrinsic rate of increase (r_m) and finite rate of increase (exp. r_m) ranged between 0.087 and 0.210 and 1.091-1.233, respectively. The German strain might be a potential candidate for mass rearing and releases against the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), due to its high net reproduction rate (R₀=10.65 female), a high intrinsic rate of natural increase (r_m=0.210), a high finite rate of increase (exp. r_m=1.23), and a short population doubling time (D_t=3.3 days). The relevance of intra- and interstrain variability as well as the usefulness of fertility life tables for pre-introductory research is discussed.