The endocrine basis of reproductive inactivity in Monarch butterflies overwintering in central California

Monarch butterflies (Danaus plexippus) collected during winter in central California are reproductively inactive. Oögenesis is stimulated in such animals by environments simulating summer conditions. Allatectomized or neck-ligatured winter animals do not normally undergo oögenesis when placed in summer conditions, but apparently normal oögenesis occurs if they are injected with juvenile hormone isomers. Injections of such isomers into winter animals held in environments simulating winter also promote oögenesis, even though winter conditions typically inhibit ovarian development. Reproductive dormany in winter Monarchs of central California therefore appears to be due (at least partially) to environmentally induced inactivity of the corpora allata.