none In this paper, the authors propose two non-destructive methods for estimating the original number of eggs laid in a host (hereafter, N sub(e)). The first method is to calculate N sub(e) by measuring the oviposition time (t). Ikawa and Suzuki (1982) found a positive correlation between t and N sub(e) in the case of single oviposition. In this paper, they will show that this relationship between t and N sub(e) is highly linear and holds a wider range. Therefore, they can estimate N sub(e) from the measurement of t, with small error. Second, the sum of the parasitoids which left the host and those which failed to leave can be an estimator of N sub(e), as is used by Matsuzawa (1958).