Butterfly forage plants

     Above: a young larva of Heliconius charitonia (zebra butterfly) feeds on Passiflora platyloba, which occurs in the low land of Panama and Mexico. Normally, P. platyloba has three-lobed leaves but it is also seen with entire heart shaped leaves. The up to 1.5 cm long linear stipules have orange-yellow tips, which may be a little reminiscent of butterfly eggs, however, without intimidating H. charitonia from laying eggs.

     Larvae of Heliconius charitonia like to eat young growing leaves, which they eat from the tip of the leaf and some way down along the main vein (midrib) before it moves to another young growing leaf. Above, a left behind mature leaf is shown.

Mature Heliconius species forage among others on Gurania makoyana (Cucurbitaceae).

     Many butterflies in particular from the South- and Central American genus Heliconius lay eggs on the leaves or other parts of Passiflora plants, and their larvae eat the leaves. Several Heliconis species are so closely connected to Passiflora that they only lay eggs on one or very few Passiflora species.

     Some Heliconis species (among others H. charitonia shown above) place just one egg per leaf, while others lay large collections of eggs. Heliconius butterflies are specialized on Passiflora leaves as food despite the plants containing different cyanogenic glycosides. When these agents are subjected to the digestive enzymes, they split into deadly poison such as hydrogen cyanid. This keep away many plant eaters from Passiflora, but Heliconius larvae can in defense neutralize and store the poisonous degradation products and thereby get the plants for themselves.

     The variable leaf shape from species to species may be an evolutionary adaptation protecting the plants from being eaten by butterfly larvae. Butterflies use sight and hence leaf shape to identify suitable host plants. Some climbing Passiflora species can hide from butterflies if they have a leaf shape which mimics the leaf shape of the supporting plant. Extrafloral nectaries and even certain stipules can also exhibit mimicry and look like butterfly eggs. In this case the butterflies will not lay eggs on adjacent leaves since they detect a danger for insufficient food for the larvae when eggs (although false) are already deposited on the plant. Heliconius larvae eat for 2-3 weeks before they pupate. Further 8-12 days later they emerge as adults, which contrary to other butterflies eat both nectar and pollen. The latter is a source of protein, which allows adult Heliconius species to live up to five months.

     Heliconius species do not pollinate Passiflora, but they get nectar mostly from Lantana and species in the cucumber family (Cucurbitaceae), which they simultaneously pollinate.

Empty pupa of zebra butterfly, Heliconius charitonia, hanging below the midrib of a leaf of Passiflora platyloba.

Zebra butterfly resting on a dried tendril of P. platyloba.

     An adult zebra butterfly swarms around a pupa on the edge of a leaf of Passiflora platyloba. Several days before hatching males may sit on the pupa containing a female, so the best placed male is ready for mating on a first-come, first-served basis. – The photo is slightly unsharp since it is difficult to use a hand held tele-lens in a humid and shady tropical greenhouse.

     Heliconius cydno galanthus with a characteristic blue glow on the upper side of the wings is another Heliconius species, which lay eggs solitarily.  It is from Central America where the larvae forage on most of the Passiflora species. The main species H. cydno has many subspecies with different distribution and variable coloration on the wings.

H.S. Heide-Jørgensen, August 2011.

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