Guadeloupe, Piton de Ste-Rose, 23-IV-1984.

Female

Guadeloupe, Petit-Bourg, Domaine Duclos, -I-1983, ab ovo.

Danaus plexippus (Linnaeus, 1758)

Nymphalidae Danainae

Monarch

Systematics

Four subspecies have been described from the Caribbean. According to Smith, Miller & Miller (1994), only two of them are clearly defined. A molecular study of genetic variability is needed to confirm the limits of these taxa.
D. p. plexippus occurs in continental America, Cuba and Bahama Is., and D. p. megalippe occurs in the other Antillean islands.
However, typical D. p. plexippus may be found everywhere in the Antilles, due to the migratory behaviour and flight performances of continental populations. These continental monarchs are probably able to mate with insular populations, thus limiting the polymorphism.

Biology and distribution

Larva on Asclepiadaceae, especially Asclepias curassavica and Calotropis procera.
The tropical populations of the monarch are sedentary.

Occurs in Martinique, Guadeloupe and all their dependencies. Generally common.

Throughout the Antilles.

North and Central America (D. p. plexippus). South America (D. p. erippus).
Australia, New Zealand, India, Canary Is. and sometimes western Europe.

Legend

Pheromone and sexual behaviour

In the genus Danaus, all male butterflies have a pair of eversible androconia at the abdominal tip (coremata). These androconia produce a courtship pheromone: danaidone (2,3-dihydro-7-methyl-1H-pyrrolizine-1-one) or aldehyde analogs. The androconia are displayed in front of female antennae during courtship, to induce landing and mating.
The origin of the pyrrolizinidic alkaloids (PAs) in the androconia is a classical question in chemical ecology. Danaus larvae feed on very toxic milkweeds that do not contain PAs, whereas the adult males visit some PA plants (Boraginaceae or Fabaceae) to sequester the alkaloid precursors of their pheromones: a male reared in captivity without access to PA plants is not able to mate. The final step of pheromone biosynthesis is achieved when the male inserts his coremata into pouches on hindwings.
These alkaloids are very toxic, their accumulation in seducing organs probably acts as a defense mechanism against predators (the hemolymph of adults contains PAs, but also cardenolides from the larval food). The use of defense compounds as aphrodisiac pheromones occurs in other lepidopteran families (Arctiidae).

Contrary to other species (e.g. Danaus gilippus from Grenada and Barbados), the males of D. plexippus do not produce any alkaloid pheromone, although they have coremata and alar pouches. However, the male butterflies visit PA plants and sequester alkaloids in their hemolymph. During courtship, a third of the males display their coremata in front of the females, which behaviour seems to induce landing. The real stimulus evoked by the androconia remains unknown in D. plexippus, maybe it is only a tactile and visual stimulation.

Many works dealt with male pheromones and sexual behaviour in Danainae and Arctiidae. More specific papers may be found in bibliographic reviews: Boppré M., 1984, in The Biology of Butterflies (R.I. Vane-Wright & P.R. Ackery eds.), Academic Press, London, p. 259-275 ; Fitzpatrick S.M. & McNeil J.N., 1988, Mem. entomol. Soc. Can., 146: 131-151 ; Birch M.C., Poppy G.M. & Baker T.C., 1990, Annu. Rev. Entomol., 35: 25-38.