Experimental animals and developmental staging
P. xuthus, P. machaon, and P. polytes was purchased from Eiko- Kagaku (Osaka, Japan), kindly provided by Dr. Akira Yamanaka (Yamaguchi University, Japan), or collected from the field. Larvae were reared on leaves of Zanthoxylum ailanthoides (Rutaceae) for P. xuthus, Petroselium crispum for P. machaon, and Citrus Pa- radis for P. polytes at 251C under long-day conditions (16 h light/ 8h dark). The staging of molting period was based on the time when head capsule slippage (HCS) occurred, as well as spiracle index, which represented the characteristic sequence of new spiracle formation (Fig. 1D, Kiguchi and Agui 1981).