How to Know a Fly, Part II: Fruit, Pomace, Names & Patterned Wings

Drosophila 'fruit fly' or 'dew fly'?

Tiny flies with red eyes hover over many a bowl of fruit. I suppose that is why we call them fruit flies, but therein reigns imprecision, confusion, and bad wine. I suppose the most well known fruit fly must be Drosophila melanogaster Meigen, 1830, because it inhabits biology and genetics textbooks the world over. My translations of the genus and species names are ‘dew lover’ and ‘black belly’, neither exactly fruity, but seemingly in agreement with other translations. Carl Fredrik Fallén proposed the name Drosophila in 1823 with Musca funebris Fabricius, 1787, as the type species. Funebris is Latin for funeral or death. That would seem to leave us with the equally fruitless ‘Death’s Dew-Lover’ as the type species of the type genus of the 'fruit fly' family Drosophilidae. No wonder, many entomologists, especially if they work in horticulture or quarantine, use ‘Fruit Fly’ for another family: the Tephritidae.

Adult Apple Maggot - a real Fruit Fly (Tephritidae)

Admittedly, although the Tephritidae does contain many economically important pests of fruit, the name may be derived from the Greek for ashes or ash-coloured. Species of Tephritis Griffith & Pidgeon, 1832, do not occur in the Home Bug Garden, but another tephritid fly in the same tribe and with similar habits and similar looks does: Campiglossa albiceps (Loew, 1873). Like species of Tephritis, the maggots of this fly inhabit the 'flowers' (actually heads of many small florets) of plants in the Asteraceae (asters, daisies, goldenrod etc.) and eat the seeds (achenes), but to a botanist achenes are the fruits, so we have some consistency.

Campiglossa albiceps - a tephritid Fruit Fly of ashy mien?

No joy for the etymologist with Tephritidae, but I’m not the only one to find the conjunction of ‘fruit fly’ and Drosophila objectionable. The eminent geneticist MM Green (2002) has a delightful rant in the journal Genetics on the diversity of habitats infested by drosophilid ‘fruit flies’. Perhaps the only thing that ties together the ecology of most species of Drosophila is a fondness for rotten things. Green points out that ‘Pomace Fly’ was the preferred common name in 20^th Century genetics texts until the Roaring Twenties when ‘Vinegar Fly’ and the infamous ‘Fruit Fly’ started slugging it out.

Scaptomyza sp. a drosophilid 'fruit fly' that breeds in rotting leaves

As anyone who has allowed Drosophila to get into his or her fermenting mash might know, Vinegar Fly is an all too appropriate name: Drosophila carry the microbes that compete with wine yeasts. Pomice, the mush leftover after fruit hs been juiced, also makes a nice base for a common name. For most of the flies in the family Drosophilidae whose larval habits are known, it is the rot in the fruit  that makes their habitat. The maggots tend to feed on the yeasts and bacteria that develop (probably after having been introduced by adult flies) in spoiled or damage leaves, fruit, nuts, cacti, sap fluxes, mushrooms, and similarly liquefying plant substrates. Perhaps Fallén knew what he was writing about.

Leucophenga sp. a drosophilid 'fruit fly' associated with mushrooms

But even if Fallén was trying to make his name reflect the behaviour of his species, why should we care? Common names are not for scientists. Besides, generalizing about the habits of a family of insects, or even a genus, is likely to lead to error. There are drosophilid maggots that eat fresh water algae, hang out in the gills of land crabs, live in flowers, mine leaves or stems, and even one or two species that attack fresh fruit. Evolution tends towards the opportunistic and if the right opportunity presents itself an insect is likely to try and take it on. An example of opportunism is the drosophilid Chymomyza amoena (Loew, 1862) – a gift from North America to Europe. This fly breeds in a variety of fallen fruit, acorns, and nuts in Eastern North America and is now spreading through apple and chestnut orchards in Europe. Apparently, there are no European ‘fruit flies’ that fill this niche, and our native is happy to oblige (see Burla 1997, Band et al. 2005, Matteson et al. 2007 in references below).

Chymomyza ('juice fly') from AB that breeds in wounds on aspen trunks

The only Chymomyza I’ve seen in Alberta lacks the patterned wings (or boldly contrasting legs – see Eberhard 2002 in refs below) that are used for sexual signaling in both drosophilid and tephritid (and many other) flies and prefers oozing sap to fruit. However, we do have our ‘true’ Fruit Fly: the Apple Maggot (aka Railroad Worm – presumably from the winding trail of the maggot in the fruit) Rhagoletis pomonella (Walsh, 1867) to entertain us. This fly appears to have originated in North America as a maggot in the fruit of hawthorns (genus Crataegus). Like apples, to which they are related, hawthorns have attractive white flowers in the spring (the White Hawthorn is the state flower of Missouri) and red fruit that somewhat resemble tiny apples. When apples started to outnumber hawthorns, some hawthorn flies switched hosts to give us our Apple Maggot. Although watching one strut around in one's garden is not a good sign, they are far more interesting than the cabbage maggots that wreck the broccoli, turnips, and radish.

Rhagoletis pomonella - not a welcome guest, but an attractive one

Well, enough is enough. As usual, what I thought would be a simple post on a few interesting ‘fruit flies’ that might take an hour or so has led to a weekend’s worth of ‘free time’ lost to reading about bugs (instead of doing chores). And I haven’t even gotten to the really interesting things like the ability of some Chymomyza species to survive freezing to −100 °C  (see Koštála et al. 2011) or their use in exploring the ‘Timeless’ gene. I guess there are worse ways to waste one’s time, but just now I’m informed it is time for dinner and I’d better get cooking.

Campiglossa albiceps - a true fruit fly that eats flowers

References

Band HT. 1995. A note on the sympatric collection of Chymomyza (Diptera: Drosophilidae) in

Virginia's Allegheny Mountains. Great Lakes Entomologist 28(3-4): 217-220.

Band HT; Bachli G; Band RN. 2005. Behavioral constancy for interspecies dependency enables Nearctic Chymomyza amoena (Loew) (Diptera : Drosophilidae) to spread in orchards and forests in Central and Southern Europe. Biological Invasions 7(3): 509-530 DOI: 10.1007/s10530-004-6352-2

Band HT, Band RN & Bachli G. 2003. Nearctic Chymomyza amoena (Loew) is breeding in parasitized chestnuts and domestic apples in Northern Italy and is widespread in Austria. Mitteilungen der Schweizerischen Entomologischen Gesellschaft 76(3-4):307-318.

Burla, Hans. 1997. Natural breeding sites of Chymomyza species (Diptera, Drosophilidae) in Switzerland. Part II. Mitteilungen der Schweizerischen Entomologischen Gesellschaft 70(1-2): 35-41.

Eberhard William G. 2002. Natural history and behavior of Chymomyza mycopelates and C. exophthalma (Diptera: Drosophilidae), and allometry of structures used as signals, weapons, and spore collectors. Canadian Entomologist 134(5):667-687.

Green MM. 2002. It Really Is Not a Fruit Fly. Genetics 162:1-3.

Grimaldi, DA. 1990. A phylogenetic, revised classification of genera in the Drosophilidae (Diptera). Bulletin of the American Museum of Natural History 197: 1–128.

Vladimír Koštála , Helena Zahradníčkováa,& Petr Šimeka. 2011. Hyperprolinemic larvae of the drosophilid fly, Chymomyza costata, survive cryopreservation in liquid nitrogen. PNAS 108(32): 13041–13046.

William Mattson, Henri Vanhanen, Timo Veteli, Sanna Sivonen & Pekka Niemela. 2007. Few immigrant phytophagous insects on woody plants in Europe: legacy of the European crucible? Biological Invasions 9:957–974 DOI 10.1007/s10530-007-9096-y