These delightfully coloured, red, yellow and black Delias species – such as the Red-spot Jezebel (Delias descombesi descombesi) (above) – are widely thought to be poisonous, or at least unpalatable, and the colour patterns are therefore aposematic, i.e. a warning signal to potential predators. I was surprised therefore, to discover that until recently, the evidence for their unpalatability was largely circumstantial (Orr, 1990). A recent study by Jocelyn Wee and Antónia Monteiro (at the National University of Singapore) has however, confirmed that these red and yellow colours do function as warning signals – in the Painted Jezebel (D. hyparete)(below) – and protect this butterfly from predation.
The study by Wee and Monteiro also showed that red patches on the ventral (under) sides of Delias spp. wings are probably a slightly more effective colour – than yellow for example (although patterns work better than blocks of colours, see previous blog) – in terms of providing warning/protection. In addition, they showed that red seems to have evolved more recently as a warning colour in this lineage of butterflies, i.e. compared to the yellow, white, and black colours also found on Delias butterfly wings. The question now is, to what extent can we be confident of extrapolating this finding of aposematism in D. hyparete, to other, similarly coloured species in the same genus?
Larvae of species in the genus Delias feed primarily on mistletoe like plants – hemiparasites – in the family Loranthaceae and to a lesser extent on the Santalaceae and Viscaceae (Braby et al., 2006). For example, larvae of the beautiful Delias harpalyce (below) feed on a showy mistletoe called Muellerina eucalyptoides, which is parasitic on Eucalyptus haemastoma (Braby & Douglas, 1992). Although some researchers have speculated on the possible nature of the toxins contained in these host plants (e.g. see Braby & Trueman, 2006) the chemical nature of the toxins is not known (Orr, 1999).
It is probably worth emphasizing that these bright colours are on the undersides of the wings (see below). That means that they are very apparent and highly visible when the butterfly is resting on a leaf with its wings closed. The upper (dorsal) sides are however, rather plain – shades of black and white (see below) – and not involved in aposematic signalling.
It is also worth mentioning in passing, that males of these aposematically coloured Delias species are generally brighter than females, so it is very possible that, as in passion-vine butterflies like Heliconius erato, the ‘seductive colours‘ (Finkbeiner et al., 2014) are also used in attracting mates.
The colours on many of these Delias species are often different patterns of red, yellow and black – refer to ‘Delias of the World‘ for example, or just Google Delias butterflies! Personally, I think it is fair to assume that many, if not most of these colourful species will be aposematic. N.B. there are many pierid mimics of these Delias butterflies which are palatable (such as Prioneris sita), i.e. not protected by toxins, but that is another story.
As a final point, it is worth noting that a paper published by a Victorian ornithologist named Frank Finn, in 1897, in the Journal and proceedings of the Asiatic Society of Bengal, demonstrated that adult Delias eucharis Drury were rejected or avoided by avian predators. Finn tried feeding a variety of butterflies to a number pf caged birds! For example:
“I gave the Bhimraj [Hindi name for the Greater Racket-tailed Drongo (Dicrurus paradiseus)], which was not hungry, a Delias eucharis, which it tried and refused, repeating the refusal when the insect was again offered ….. In the morning I saw the Bhimraj look at, but
not touch, the Delias eucharis … which had been left in its cage from yesterday.” Finn, F. (1897).
Braby, M. F. (2006). Evolution of larval food plant associations in Delias Hübner butterflies (Lepidoptera: Pieridae). Entomological Science, 9(4), 383-398.
Braby, M. F., & Douglas, F. (1992). Observations on the biology of’Delias harpalyce'(Donovan)(Lepidoptera: Pieridae) near Melbourne, Victoria. Australian Entomologist, The, 19(1), 9.
Braby, M. F., & Trueman, J. W. H. (2006). Evolution of larval host plant associations and adaptive radiation in pierid butterflies. Journal of evolutionary biology, 19(5), 1677-1690.
Finkbeiner, S. D., Briscoe, A. D., & Reed, R. D. (2014). Warning signals are seductive: relative contributions of color and pattern to predator avoidance and mate attraction in Heliconius butterflies. Evolution, 68(12), 3410-3420.
Finn, F. (1897). Contributions to the theory of warning colours and mimicry. No. IV. Experiments with various
birds. Summary and conclusions. J. Asiat. Soc. Bengal 66, 613–668. Available online: https://library.dbca.wa.gov.au/static/Journals/080943/080943-66.02.pdf
Orr, A. (1999). Evidence for unpalatability in the genus Delias. Australian Entomologist, 26(2), 45-52.
Wee, Jocelyn Liang Qi, and Antónia Monteiro. Yellow and the novel aposematic signal, red, protect Delias butterflies from predators. PloS one 12.1 (2017): e0168243.