Demography and Life History of the Egg Parasitoid,Trichogramma brassicae, on Two MothsAnagasta kuehniellaandPlodia interpunctellain the Laboratory

Abstract

The egg parasitoid, Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) is the most important and widely distributed species of Trichogramma in Iran. It attacks eggs of several lepidopterous pests, and is a major biological control agent. Rearing parasitoids is necessary for experimental work, and, potentially, for mass release in the field. Selecting a suitable host is critical for developing a successful rearing method. If other conditions are the same, the rate of population increase will be a suitable indicator of parasitoid performance on different hosts. However, conclusions based on a single generation can be misleading because of the learning ability of parasitoids. Life history parameters of T. brassicae were studied on two hosts easily reared in the laboratory, Anagasta kuehniella Zeller, and Plodia interpunctella Hübner (Lepidoptera: Pyralidae). All the experiments were carried out at 24 ± 1°C, 65±10% RH, and 16:8 L:D photoperiod. Eight parameters including gross and net reproductive rates (GRR and R0 respectively), intrinsic rate of natural increase (rm), finite rate of population increase (λ), intrinsic birth and death rates (b and d respectively), cohort generation time (T), and doubling time (DT) were compared between two hosts for two generations. All parameters showed a highly significant difference (α = 0.01) between hosts. GRR, R0, rm, λ, and b were higher, while d, T, and DT were lower in Anagasta than Plodia. The intrinsic rate of natural increase was 0.2912 and 0.2145 female/female/day and net replacement rate was 45.51 and 19.26 female/female/generation in Anagasta and Plodia respectively. Differences between generations were significant except for rm, λ, and d. The net replacement rate was 28.56 and 39 in the 1st and 2nd generations respectively. These results showed that A. kuehniella was a better host than P. interpunctella. Higher reproduction occurred in the second generation that may be due to increased adaptation to experimental conditions.