Abstract
Using Aphis craccivora KOCH (Aphididae) as prey, H. axyridis larvae were reared individually from hatching at various prey densities (w) in a dish. The number of preys eaten by a predator per day (x), the duration of instar (duration to next instar or to death) (y), and the survival rate (Z) in each instar were recorded. The percentage predation by each instar, Pnw%={(x×y)/(w×ln)}×100 (ln: mean maximum duration of n-th instar) was supposed to increase initially, then later decreased with increasing prey density. The percentage predation by each instar following the immediately preceding instar, Qnw%={(x×y×Zn-1)/(w×ln)}×100 (Zn-1: survival rate to n-th instar from (n-1) th instar) increased initially, then decreased with increasing prey density. The percentage predation by whole larval instars, Rw%={1004Σn=1(x×y×Zn)}/(w×L) (Zn: survival rate at n-th instar from hatching, L: mean maximum larval duration) increased initially, then decreased with increasing prey density. Therefore the developing larvae of H. axyridis can act as a density-dependent mortality in a range of prey density. But when percentage predations were relatively high, the predators starved.