One host—one parasitoid system: Seasonal life cycles of Pryeria sinica (Ledipoptera) and Agrothereutes Minousubae (Hymenoptera)

Summary The zygaenid Pryeria sinica Moore and the ichneumonid Agrothereutes minousubae Nakanishi form a one host—one parasitoid system in nature. Their seasonal life cycles were investigated by laboratory experiments and field observations, and the life‐cycle adaptation of the parasitoid to its host was examined. The moth is univoltine. The larva hatches from mid‐February to mid‐March and feeds on leaf buds and young leaves of ever green Euonymus japonicus Thunb . The thermal constants for completing the 1st, 2nd, 3rd, 4th larval instars and prepupal stage were 85.6, 80.5, 85.2, 177,0 and 197.6 degree‐days, respectively. The prepupa and pupa vulnerable to the attack by the parasitoid occurred from mid‐April to early May and from mid‐ to late May, respectively. Diapause in the parasitoid is facultative and occurs in the eonymphal stage. The photoperiodic response for this diapause was a long‐day type with a critical photoperiod of 13 hr 40 min at 20°C, but it was not expressed at 25°C, most larvae entering diapause irrespective of photoperiod. About 19, 120, 82 and 112 degree‐days above 7°C were required to complete the egg, larval, prepupal and pupal development, respectively. These data were superimposed on the photothermograph of Fukuoka, and it is predicted that the 1st adult eclosion would occur in late April and the partial 2nd adult eclosion in early June. The prediction was supported by field observations. The adult eclosion of the parasitoid synchronized well with the apperance of prepupae and pupae of the moth. The parasitoid has two types of seasonal life cycle, one generation and two generations a year. Both types have an extremely long dormant period of 10–11 months due to aestivo‐hibernation. This seasonal life cycle enables the parasitoid to maintain its population when the host is in short supply.