Estimating female reproductive success of a threatened butterfly: influence of emergence time and hostplant phenology.

We estimated lifetime reproductive success of Euphydryas editha bayensis (Nymphalidae), a federally listed threatened butterfly, based on age-specific fecundity and both adult and offspring survival. Our results indicate that the relative timing of adult emergence and larval hosplant senescence strongly influenced reproductive success of females. For 1992, we estimated that only 8-21% of the eggs laid by females emerging on the 1st day of the 4-week flight season would produce larvae that reach diapause. This figure dropped to 1-5% for females emerging 7 days into the flight season. Within our entire sample, we estimated that 64-88% of the females produced offspring with less than a 2% probability of reaching diapause. These estimates are particularly striking given that they are based on only one source of larval mortality - prediapause starvation due to hostplant senescence. This dependence of reproductive success on the relative timing of female emergence and hostplant senescence may reduce effective population size and render E. editha bayensis especially vulnerable to local extinction events.