Wednesday, September 1, 2010

Sunday Sawfly: A Dolerus deceptively not interested in a Mayday

The middle of the week is about as far from Sunday as one can get, but last Sunday I was overworked and this Sunday I’m on holiday, so I’m serving two Sundays with one small black sawfly. Dave Smith has identified this as a species of Dolerus (a genus with almost 200 described species, including about 75 in the Nearctic) and possibly the introduced European species D. nitens Zaddach. Dave doesn’t have records of this sawfly from Alberta, but it is sawing its way across North America, so was bound to get here sooner or later. This picture was taken on a Mayday bud in the process of opening in early May – what passes for early spring most years in Alberta. Dolerus nitens is known to be one of the very early emerging sawflies, but it does not feed on Mayday (Prunus padus) or other cherries or plums.

With its somber black colour, it is tempting to think that Dolerus comes from the Latin for sorrows (dolor), but ‘doler’ is Greek for ‘deceptive’. The genus was named by Panzer, presumably the famous German botanist and entomologist Georg Wolfgang Franz Panzer who died in 1829. Perhaps he was referring to something deceptive about the larvae. The caterpillar-like larvae of D. nitens graze on grasses (Poaceae) and sedges and their relatives (Cyperaceae) and are considered pests in grains. The Home Bug Garden has a few clumps of ornamental reed grasses (Calamagrostis), one clump of a native needle-grass (formerly in Stipa), and a pond-full of spike-rush (Eleocharis) and sedge (Carex). Species of all of these genera are suitable hosts for D. nitens, so we may one day be able to be decode the deceptive name.

I’ll end this short post with an even shorter digression, stumbled upon while searching (with little success) for some biological information on D. nitens. It seems that sawflies are one of those interesting entomological groups that are more diverse in the cooler parts of the World (or at least of its northern half) and become less diverse as one moves towards the tropics*, reversing what one normally expects of insect diversity. I suppose that helps to explain why the Home Bug Garden seems so blest with sawflies, while in Queensland I can't even remember seeing one.
*Kouki et al. 1994. Reversed latitudinal gradient in species richness of sawflies. Ann. Zool. Fenn. 31: 83-88.

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