Abstract
Since the larvae of the peach fruit moth, Carposina niponensis WALSINGHAM, eat into fruits just after hatching from eggs, it is difficult to distinguish the instars in the larval stage. In the present paper, an attempt was made to determine the instar of the larvae which were reared under a constant temperature in the laboratory as well as collected in fields by measuring the width of the head capsule. The results obtained are summarized as follows:
1. In both the first and the second broods, the frequency distribution of the width of head in the laboratory samples is composed of four independent mountain-shaped curves, which correspond to the four different instars of the larvae. This is also the case in the larvae collected from fields at random.
2. The ratio of the mean head width between each instar and the preceding one, which is sometimes called growth ratio, shows a tendency to diminish slightly with advancing age in the first brood. But no uniform tendency is found in the second brood, and the ratio between the second and the third instars is largest.
3. When the larvae of the first brood are fed on the fruit under a constant temperature of 22±1°C, the larvae complete their development in 15 days. In the second brood the larvae complete their development in 17 days at 21±2°C.
4. Three formulae for growth, DYAR'S, TOKUNAGA'S and GAINES & CAMPBELL'S formulae, were examined for their applicability to the present case. It was found that GAINES & CAMPBELL'S formula best fits the case.
