Evidence for reproductive diapause in the fritillary Speyeria idalia (Lepidoptera : Nymphalidae)

Reproductive characteristics of a northeastern Kansas population of the fri tillary Speyeria idalia (Drury) were studied. Hemolymph juvenile hormone (J H) titers, ovarian development, and fat body utilization were monitored wee kly in adult females over their entire 1997 flight period, which extended f rom mid-June to early October. Dissections of female reproductive systems r evealed that S. idalia females mate just once, soon after they emerge in mi d- to late June. Gas chromatographic-mass spectrometric determinations of j uvenile hormone suggested that they undergo a reproductive diapause through mid-August related to the absence of or very low titers of juvenile hormon e. Oogenesis and fat body. depiction do not commence until late August/earl y September, soon after which oviposition occurs. The onset of oogenesis co incides with a rapid rise in hemolymph titers of JH I, JH II, and JH III. T he predominant juvenile hormone homolog was IH II, but both JH I and JH III exhibited smaller, concomitant peaks. Four fundamentally different lepidop teran reproductive strategies have been recognized based on various reprodu ctive characteristics and the type of gonadotropic hormones used to stimula te oogenesis. Speyeria idalia exhibits a type of reproductive strategy that has not been documented in Lepidoptera, typified by protandry, female mona ndry, long-lived (>8 wk) females that feed throughout their adult lives, gr eatly delayed oogenesis that occurs late in adult life, and apparent juveni le hormone control of gonadotropic processes. This reproductive strategy ap pears to be an adaptation to the phenology of larval host plants, namely co ordinating the life cycle with that of the seasonally restricted violets on which larval survival of this monophagous species depends.