As noted in an earlier post, most people's perception of Lepidoptera, 'butterflies and moths', is heavily skewed towards the larger members of the group while the greater diversity is actually to be found among the smaller species (this sentence, offhand, could be repurposed for just about any animal group). The subject of today's post, the Yponomeutoidea, are a clade of about 1800 species of the much-overlooked smaller Lepidoptera. Yponomeutoids have been recognised as a group primarily on the basis of a single synapomorphy, the presence of posterior lobes on the eighth abdominal pleura (a 'pleuron' being a sclerite on the side of the body wall). This character has been secondarily lost in some subgroups of the Yponomeutoidea, but the clade is also supported by molecular data (Sohn et al. 2013). The larvae of yponomeutoids are plant-feeders, with the clade including some species that feed internally as leaf-miners or stem-borers, and others that feed externally on leaves though they do conceal themselves within a silk webbing. A number of species are effectively both, starting out as internal leaf borers then changing to external leaf webbers as they grow larger. Some species are notable horticultural pests, such as the diamondback moth Plutella xylostella that attacks brassicas*.
*Horticulture is the only human endeavour in which you will hear something described as 'attacking' a cabbage.
The most recent review of the clade's systematics by Sohn et al. (2013) recognised eleven families within the Yponomeutoidea, but this was not the first re-organisation of the yponomeutoids and it will probably not be the last. Many of the families have few distinct synapomorphies, and a few recognised by Sohn et al. lack recognised morphological synapomorphies altogether and are united by molecular analysis only. Most yponomeutoids follow the usual microlepidopteran pattern of being small and generally brown, but there are some exceptions. The 'mega-plutellids' of New Zealand and Tasmania (placed by Sohn et al. in the family Glyphipterygidae rather than Plutellidae) are relatively large, with the Tasmanian Proditrix nielseni having a wingspan of over six centimetres (McQuillan 2003). The adult of the ailanthus webworm Atteva pustulella has a fairly striking array of black-ringed white patches on an orange background.
Though the clade is diverse in its habits overall, feeding habits tend to be conserved within each of the constituent families. It is not entirely clear whether internal or external feeding represents the original lifestyle of the yponomeutoids, though there may be a slight tip towards internal feeding. If this is the case, then external feeding has arisen within the yponomeutoids on a number of occasions, and the pine needle miners of the genus Zelleria in the family Yponomeutoidea probably represent at least one case of a internal feeder derived from externally feeding ancestors. Some families show a bias towards particular plant hosts: the Attevidae are primarily found on Simaroubaceae, while the Bedeliidae show a preference for Convolvulaceae. Others are more diverse in their selection.
McQuillan, P. B. 2003. The giant Tasmanian ‘pandani’ moth Proditrix nielseni, sp. nov. (Lepidoptera: Yponomeutoidea: Plutellidae s. l.) Invertebrate Systematics 17: 59-66.
Sohn, J.-C., J. C. Regier, C. Mitter, D. Davis, J.-F. Landry, A. Zwick & M. P. Cummings. 2013. A molecular phylogeny for Yponomeutoidea (Insecta, Lepidoptera, Ditrysia) and its implications for classification, biogeography and the evolution of host plant use. PLoS One 8(1): e55066. doi:10.1371/journal.pone.0055066.