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Passiflora Passion flower – Butterflies – Heliconius
Some butterflies visit Passiflora to drink nectar from the flowers and some also may eat the pollen, in doing so they may rarely also pollinate the flowers. We all love butterflies but their caterpillars can wreak havoc, rapidly defoliating and sometimes killing Passiflora. There is a special relationship between Passiflora and the Heliconius butterflies, also known as longwings, that demonstrates the complexity of the ongoing battle.
Passiflora ‘Betty Myles Young’ totally defoliated by caterpillars in two weeks.© Daryl Draper 2018
If your Passiflora are being destroyed by butterfly caterpillars, such as the Gulf fritillary, Agraulis vanillae, above, eating them, you can pick some/all off by hand wearing suitable protection. Warning! While caterpillars are quite safe if you leave them alone, many caterpillars have urticating (irritating) hairs either by touch or inhalation. To avoid problems wear protective gloves, cover your arms and ideally also wear a mask and cover the eyes. This sounds a bit extreme but some allergic reactions to caterpillars can be quite severe.
Rather than kill the caterpillars try to keep one or two large Passiflora that they can be moved to and eat without you worrying. Remember no caterpillars = no beautiful butterflies!
Note, if the worst comes to the worst and it is kill or be killed, I would recommend Bacillius thuringiensis (Bt) in spray form. It is a microbe found naturally in the soil. There are many different strains of it depending on what you want to target, and they are generally quite specific to that target, e.g. ‘kurstaki’ for caterpillars.
Passion flower defences
There is an extraordinary special relationship between Passiflora and the Heliconius butterflies known as Longwings, Nymphalidae, Heliconiinae, Heliconiini. Theirs is a uniquely uneasy relationship however with a constant battle of wits as above. These beautiful insects, which often appear to fly in slow motion, on occasion lay their eggs on passion flowers. The eggs are usually laid singly, though sometimes in groups.
The caterpillars, which may have irritant spines, then hatch out & eat the leaves of the plant. In sufficient numbers they will destroy it. At the same time however in some species the adults may rarely pollinate the flowers. They are the only butterflies that both eat pollen and drink nectar and may live for up to 9 months.
I am greatly indebted to Dr L. E. Gilbert for his assistance in updating the information on this page.
Larry Gilbert comments,
‘Overall use of Passiflora flowers by Heliconius is rare and very exceptional. People tend to photograph it when they see it in butterfly houses. In rain forest habitats with pollen sources like the cucurbits Psiguria (Anguria) and Gurania, and rubiads like Psychotria and Palicourea Heliconius are the key pollen and nectar sources. Heliconius are seen visiting only a few other things for pollen. Cissis, Lantana, and miscellaneous other adult resources are frequented for nectar and some pollen but these are competed for by many other kinds of butterflies.’
The plants have a number of different defences to try to prevent butterflies laying their eggs on them. The eggs hatch out into voracious caterpillars which can severely damage or even kill the plants. The sophistication of the defences gives an insight into the evolutionary pressures on these plants. Defences include:-
Heliconius egg mimicry, yellow egg-like structures or spots (about 1 mm diameter) on the leaves, stipules, bracts, tendrils etc and growing tips as shown above on P. actinia. Any butterfly that sees eggs from another butterfly on a plant will not lay its own eggs as they would hatch after the ones already there and would have little food i.e. leaves to eat. More importantly Heliconius caterpillars are aggressively cannibalistic both towards other younger caterpillars and indeed eggs.
In the case of P. pinnatistipula perhaps another tactic, mimicry of an insect predator which might eat the eggs.
Larry Gilbert comments,
‘The evolution of egg mimicry has happened independently 9 or 10 times judging from the many unrelated structures from which they are derived. Egg predation by con-specific larvae and the rejection of shoots with pre-existing eggs by females is the selective force. Again see the Sci Amer 1982 for a good discussion. Note that cluster laying species (H.sara on P. auriculata, H. euleuchia on P. macrophylla or P. tica, and H. sapho or hewitsoni on P. pittieri) could care less about egg mimics. Species that lay single eggs are the drivers.’
Drooping growing tips
A drooping growing tip on P. helleri typical of many passion flowers. This may suggest to butterflies & other predators that the plant is in poor condition & wilting & so is less appealing either as a snack or as a future food source for eggs that may then be laid elsewhere.D
Changing leaf shape.
Butterflies have very sharp eyesight and look for leaf shapes that match their template of what a suitable plant for egg laying should look like. A number of Passiflora change their leaf shape to try to throw them off the track. P. suberosa is well known for this and there are a nice sequence of different leaf shapes on P. colinvauxii here. Even the Common Passion Flower P. caerulea varies its number of leaf lobes.
Many Passiflora produce nectar both in the floral nectaries, and at extra-floral nectaries such as the petiole glands above. These are very attractive to ants and Smiley (1985) suggests that the presence of ants increases caterpillar mortality.
Trichomes are epidermal outgrowths on plant foliage which are often hair or scale like. In the case of a very few Passiflora, such as P. adenopoda and P. lobata, they are hooked hairs.
Larry Gilbert (1971) reports
‘Heliconius larvae die from entrapment in the hooks of the trichomes of Passiflora adenopoda.’ Further he notes (1982) that ‘several Passionvine butterflies are now know to be “hooked trichome specialists” namely Dione moneta and Heliconius charithonia. They can feed on other things but they are adept at defeating the hooks that kill most other species.’
Toxic foliage and fruit
Foliage which becomes toxic when attacked by herbivores from caterpillars to donkeys. Fruit which remain toxic until they are ripe. Larry Gilbert comments ‘Chemical protection is as interesting as the morphological traits. We know much less about this aspect.’ See Engler et al (2000). Read more
Engler, H. Spencer, K. & Gilbert, L.E. (2000) Insect metabolism.
Preventing cyanide release from leaves Nature 406: 144.
Gilbert, L.E. 1971. Butterfly-plant coevolution: Has Passiflora adenopoda won the selectional race with heliconiine butterflies? Science 172: 585-586
Gilbert, L.E. 1982 The coevolution of a butterfly and a vine. Scientific American 247:110-121.
Smiley, John T. 1985. Heliconius Caterpillar Mortality during Establishment on Plants With and Without Attending Ants. Ecology 66:845–849