Less attention has been paid to the parasitoid-host system in which the host occurs in considerably high density with a hierarchical patch structure in studies on time allocation strategies of parasitoids.This study used the parasitoid Meteorus pulchricornis (Wesmael) (Hymenoptera: Braconidae) and the Oriental leafworm,Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) as the parasitoids-host model system to investigate patch-leaving mechanisms as affected by the high host density,hierarchical patch structure,and foraging behaviors on both former and current patches.The results showed that 3 out of 8 covariates tested had significant effects on the patch-leaving tendency,including the host density,ovipositor insertion,and host rejection on the current patch.The parasitoid paid more visits to the patch with high-density hosts.While the patch with higher host densities decreased the leaving tendency,the spatial distribution of hosts examined had no effect on the leaving tendency.Both oviposition and host rejection decreased the patch-leaving tendency.The variables associated with the former patch,such as the host density and number of ovipositor insertions,however,did not have an effect on the leaving tendency.Our study suggested that M.pulchricornis females may use an incremental mechanism to exploit high density patches to the fullest.