Taxon of the Week: Butterflies on Parasites

This week I've got something a little more recognisable to go on, at least in general - butterflies! I've referred to butterflies in the past as "honorary vertebrates", as they seem to be about the only group of invertebrates that receive as much attention and recognition as vertebrate groups seem to. What those of us in the know can tell you, though, is that really butterflies are just a flashy kind of moth. Specifically, today I'll be looking at butterflies of the genus Delias.

Delias, commonly known for no particular reason as 'jezebels', are found from southern and south-east Asia to the northern tip of Australia (the image above is of Delias aglaia and is from Answers.com). The bright colouration in the photo above is usually restricted to the underside of the wings, while the upper side is far plainer - most often white with black edging, as shown in the illustration below (from Wikipedia) of Delias aganippe (a notable exception in Australia is Delias aruna, which has the upper surface of the wings bright orange-yellow). Nevertheless, they appear to be among the more colourful members of the generally modest family Pieridae, which may be best known to many of you by the cabbage whites of the genus Pieris.


There are a large number of species of Delias (I couldn't be bothered actually counting them up) placed in 23 species groups. If you want to know exactly what they all are, I'd recommend looking at Les Day's exceedingly thorough site dedicated to Delias at http://www.delias-butterflies.co.uk/. The caterpillars feed on mistletoes (hence the title of this post), which makes them notable from a conservation point of view - many mistletoes are rare and/or endangered (their thick, fleshy leaves make them very attractive to browsers), and if a species of mistletoe goes extinct then its specialist herbivores go extinct as well. While most members of Pieridae lay eggs singly, Delias lay their eggs in large clusters. The caterpillars come in a range of colours, and have long white hairs - the photo here from Wikipedia of Delia eucharis caterpillars shows both the hairs and their gregarious habits. The chrysalis is brightly-coloured, usually bright yellow or orange.

Many species of Delias have seasonal varieties, with the dry-season or winter variety being darker above, or having the underside more cryptically coloured. Studies in other Pieridae have shown that rather than being genetically determined, these variations appear to be determined by the photoperiod the larva is exposed to during development, specifically during the third and fourth instars (Hoffmann, 1973). Experimental manipulation of photoperiod exposure has even been able to induce 'seasonal variation' in species that are univoltine (only one generation per year) instead of multivoltine (multiple generations per year - Shapiro, 1977).

REFERENCES

Braby, M. F. 2004. The Complete Field Guide to Butterflies of Australia. CSIRO Publishing: Collingwood (Australia).

Hoffmann, R. J. 1973. Environmental control of seasonal variation in the butterfly Colias eurytheme. I. Adaptive aspects of a photoperiodic response. Evolution 27 (3): 387-397.

Shapiro, A. M. 1977. Evidence for obligate monophenism in Reliquia santamarta, a Neotropical-alpine pierine butterfly (Lepidoptera: Pieridae). Psyche 84: 183-190.