The effect of population density on the reproduction of Trichogramma japonicum Ashmead (Hymenoptera: Trichogrammatidae)

Summary When a fixed number of the hosts, the eggs of the almond moth were exposed experimentally to various numbers of the parasites, Trichogramma japonicum, the following changes were observed with increasing parasite density: The percentage of parasitism rises and approaches to 100 with gradually diminishing rate. The number of parasite progeny increases and reaches a maximum, then decreases gradually. The number of eggs laid per parasite female decreases gradually. The proportion of hyperparasitized hosts progressively rises. The frequency distribution of parasite eggs in a host is of an intermediate type between random and uniform. The competition among parasite larvae becomes severe. The progressive rise in mortality, the declining percentage of females in progeny and the emergence of stunted adults at the higher densities are observed. In connection with both the nature of the parasitizing behaviour of adult and that of the competition among larvae, the nature of the density effect on the parasite population was discussed.