ESTIMATING FEMALE REPRODUCTIVE SUCCESS OF A THREATENED BUTTERFLY - INFLUENCE OF EMERGENCE TIME AND HOSTPLANT PHENOLOGY

We estimated lifetime reproductive success of Euphydryas editha bayens is (Nymphalidae), a federally listed threatened butterfly, based on ag e-specific fecundity and both adult and offspring survival. Our result s indicate that the relative timing of adult emergence and larval host plant senescence strongly influenced reproductive success of females. For 1992, we estimated that only 8-21% of the eggs laid by females eme rging on the Ist 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% prob ability of reaching diapause. These estimates are particularly strikin g given that they are based on only one source of larval mortality - p rediapause starvation due to hostplant senescence. This dependence of reproductive success on the relative timing of female emergence and ho stplant senescence may reduce effective population size and render E. editha bayensis especially vulnerable to local extinction events.