Feeding
Feeding biology of Hepialidae
Only the larval stages of Hepialidae feed. Adults have non-functional mouth parts. Most, if not all, larvae emerge from eggs deposited from a female in flight or at rest. To what extent first instar larvae may move from the site of their initial emergence is generally unknown. Larvae of pasture species appear to initially remain in the immediate vicinity of their emergence whereas forest fungal-feeders would appear to move considerable distances as first and early instar larvae are found congregating on fungal infested substrates.
Most, if not all, early instar hepialid larvae feed on dead or decaying plant tissue, or fungi in combination with dead and decaying plant tissue. Some species may also ingest fungi and fungal infested plant tissue in combination with living plant tissues. Whether any species habitually specialize on only living plant tissues has yet to be corroborated, although it appears that this does occur under laboratory conditions.
After an initial period of fungus/detritus feeding, larvae begin to feed exclusively on live plant tissues for most of their development. This transition is in contrast to most phytophagus Lepidoptera that feed only on live plant material throughout their development, and other groups that feed entirely on fungus or dead plant tissues. The early stages of larval feeding remain poorly documented for most Hepialidae and this aspect of hepialid biology has major future research potential for both the amateur and professional. Larval feeding may be divided into four principal categories where most genera will be restricted to only one.
(1) Fungal or dead plant tissue (detritus)
At least some species of Oncopera (a pasture species) and Trioxycanus (a forest species) appear to feed on plant detritus throughout development, although a combination of detritus and plant feeding cannot be ruled out. Feeding on plant detritus throughout development is probably found in only a minority of species and genra.
(2) Detritus and foliage
Several southern hemisphere genera consume ground foliage, mostly grasses and other herbaceous plants: Aoraia (New Zealand), Cladoxycanus (New Zealand), Dalaca (South America), Dioxycanus (New Zealand), Eudalaca (South Africa), Fraus (Australia), Metahepialus (South Africa), Heloxycanus (New Zealand), Oxycanus (Australia/New Guniea), and Wiseana (New Zealand). Early instar larvae feed from silk-lined tunnels among litter at the soil surface and feed on dead, decaying leaves and possibly also the leaves of live plants.
(3) Detritus and roots
Genera with larvae that feed on woody or herbaceous roots include Abantiades (Australia), Gazoryctra (North America/Eurasia), Gorgopis (South Africa), Hepialus (Europe), Hepialiscus (North Africa), Korscheltellus (North America/Europe), Oxycanus (Australia), Palpifer (eastern Asia), Phymatopus (Europe), Thitarodes (Asia), Trictina (Australia), and Triodia (Europe).
Host tissues may include the entire root, or may be confined to callus growth as is also the case with stem borers. In Korscheltellus gracilis larval feeding on the roots of conifers is restricted to tissues immediately below the bark, or to include bark for young seedlings. Larvae will consume entire micorhizal roots under laboratory conditions.
(4) Detritus, roots and stems
Larvae of the North American Sthenopis and the monotypic (and probably congeneric) Zenophassus (Cacausus) first tunnel into roots and later extend these tunnels up into the lower stem from which the adult will emerge. Feeding by early instars is unknown in Sthenopis, but early instars of Zenophassus feed on fungi and detritus.
(5) Detritus and stems
Genera known to have stem boring larvae that begin their tunnels above the ground rather than in the roots are Aenetus (Australia, NZ, NG, NC, eastern Indonesia), Cibyra (Mexico/South America), Endoclita (India/eastern Asia to western Indonesia), Leto (South Africa), Phassus (Mexico/South America), Phymatodes (western North America), Trichophassus (south western Brazil), Zelotypia (Australia), In addition, other Latin American genera allied to Phassus (e.g. Schausiana) and Cibyra (e.g. Druceiella) are likely to also be stem borers. In those species where detailed observations have been made, feeding is localized to the cambial and adjacent tissues with repeated grazing of resulting callus formation.
Grehan, J.R. 1989. Larval feeding habits of the Hepialidae (Lepidoptera). Journal of Natural History 23, 803-824.
