Induction of Reproductive Dormancy in Australian Monarch Butterflies Danaus plexippus (L.)

Abstract

Non-breeding cluster populations of Danaus plexippus (Danaidae) were monitored at five sites in the Sydney area of New South Wales for 5 years. Meteorological records showed that cluster formation was always preceded by periods of cool overcast weather, during which maximum temperatures remained below 18°C for at least 2 days. Field experiments were carried out to test the hypothesis that low post-eclosion temperatures cause reproductive dormancy in Australian D. plexippus. Butterflies were reared in the laboratory and on eclosion exposed to selected temperatures and photophases for 2-4 days before being tagged and released. Recapture data showed that high post-eclosion temperatures (19 or 28°C) inhibited long-distance flight and resulted in ovarian development, but low temperatures (15:6°C, 7:17 h) inhibited ovarian development and permitted long-distance flight. Intermediate temperatures (e.g. 15°C or 12±3°C continuously) gave mixed results. Photoperiod during or before the period of exposure to low temperature did not affect reproduction. The induction, maintenance and termination of reproductive dormancy in Australian D. plexippus are discussed.