Sunday Sawfly: Inspired by Thrifty Thursday

 One of the benefits of the long, long days around the Summer Solstice at a northern latitude such as Edmonton's is that even when the weather is miserable most of the day, a hour or two of sunshine may peak through the clouds. That may not happen this rainy Saturday, but it did during yesterday's downpours and the cool conditions were a good time to get close to some bugs. Below is the original (reduced in size for posting) image of one such shot and above my best attempt at making it interesting. The sawfly is possibly Pristiphora appendiculata (Hartig)(=rufipes Lepeletier) - the Small Gooseberry Sawfly which my wife caught ovipositing for a previous posting.

I'm not much of a bug photographer - just an upper mid-range point-and-shoot (Lumix DMZ FZ28) documentor of the Home Bug Garden. The good pictures you see here are usually from my wife's Nikon D-70 DSRL - old, but reliable body with an even older lens (60 mm AF MicroNikkor 1:2.8) and SB-21 Speedlight flash. However, one of the web's best photographers of arthropods, Myrmecos, has started a weekly series called Thrifty Thursdays on using under $500 equipment to take interesting photos of insects. This has made me feel that I should be doing a better job and this is my first attempt to deal with the cluttered background problem highlighted in the linked post. Below is what I think is a less successful effort, but for some reason I like the clutter in the upper right - makes the fly seem to be seeking shelter in the pansy from the messiness of the world.

 

Oh well, it's down to a drizzle for the moment. Time to climb the ladder and clear the gutters of those nasty sticky spruce bud caps.

Sawfly Sunday: On the Importance of Prolegs

As well as the three pairs of jointed legs on their thoraces, some immature insects have additional grasping/ambulatory organs on their abdomens called prolegs. In this case ‘pro-‘ seems to be used in its ‘before in time’ mode. Perhaps whoever coined this term in the early 1800s thought these fleshy lobes were the precursors of true legs, as some think of the lobopods in modern velvet worms. On the other hand, the OED states ‘prop-leg’ as an alternative, so perhaps proleg results from an elision. In any case, the number of pairs of fleshy abdominal prolegs is a good character for distinguishing those butterfly and moth caterpillars that feed on the surfaces of plants from those of sawflies.

There are exceptions, but a good general rule is that the caterpillars of butterflies, skippers, and moths (Lepidoptera) usually have 2- 5 pairs of prolegs. A typical arrangement is on abdominal segments 3, 4, 5, 6, and then at the end (anal proleg). Inchworms (Geometridae) are, perhaps, the most commonly noticed variant – all but the last two pairs of prolegs are absent, possibly atrophied after an ancestor took up measuring its stride. 

Then there are the strange Prominents (Notodontidae) where the anal claspers have become a kind of tail. And then the miners and burrowers that may loose all trace of prolegs.

 In contrast, most sawfly caterpillars with prolegs have them on abdominal segments 2-7 or 8 and retain the anal claspers. The rarely seen larvae of Mecoptera, the scorpionflies, may have prolegs on segments 1-8. Thus, if one can count and has a reasonable guess as to which folds of abdominal skin makes a segment, then one can usually tell an eruciform (eruca is Latin for caterpillar) larval lepidopteron or mecopteron from a sawfly without any special entomological experience.

Of course, to count the number of prolegs it helps to see them. This is a special problem in a picture and a good example of why it helps to have an idea of what the important identification characters are before one takes a picture. If you have the disk space, it is also an excuse to hold on to those poorly framed or out-of-focus shots that may have useful information for identification.

 The picture above is of a sawfly caterpillar – I know it from the shape of the head capsule and the general Gestalt (I was an entomologist for many years and some of it still sticks with me) - but how many prolegs does it have? At BugGuide, Dave Smith points out that most of the grass-feeding sawflies in North America belong to one of two genera: Dolerus and Pachynematus. Larvae of the former have an asymmetrical labrum and prolegs on segment-8; the latter have a symmetrical labrum and no prolegs on segment-8. Alas, neither the labrum nor the prolegs are visible and this id is stuck at my doleful level of Gestalt.

Sunday Sawfly: The Willow Red Bean-Gall Sawfly

A gall is the result of the interaction between a plant and a consumer of the plant that causes aberrant, tumor-like growth of plant tissues. In some cases galling results in a net benefit for the plant, e.g. the nodules with the nitrogen-fixing rhizobia bacteria that form on the roots of legumes. Some galls, especially those that deform reproductive tissues or suppress elongation of shoots, are clearly detrimental to the plant. Most of the time, though, the nature of the galling interaction is more mysterious. In the insect-plant systems that have been investigated, galls are induced by substances injected into the plant by an insect. The insects (or at least their offspring) then go on to eat the plant tissues that develop around them. So, it is tempting to think of galls as bad for plants, but the evidence to test such a hypothesis is usually just not known. Galls are often brightly coloured, red is common, and one wonders if the plants aren’t trying to attract the attention of some gleaner vertebrate (red does attract birds to fruit) or insect (many galling insects are heavily parasitized) to ‘scratch their itch’.

 Among the numerous kinds of arthropods that are known to induce galls are several hundred species of sawflies in the subfamily Nematinae (Family Tenthredinidae) that pick on species of willow (Salix) and poplar (Populus). Full-blown gallers seem to have evolved from species that cause leaves to fold or curl around their grubs. These grubs feed externally in the sense that they eat from the surface down, but are well protected inside the deformed leaves. The more derived types of galls are consistently formed by particular lineages of sawflies, and the most derived type of gallers seem to be the sawflies that induce deformities in stems, buds, or leaf petioles where the grubs feed internally. 

Members of the genus Pontania (in the broad sense) are intermediate and form blister-like structures on the leaf blade inside which their grubs feed (see Nyman et al. 2000* for all the details). Pontania proxima (Lepeletier) (a complex of similar species in Europe and possibly here) form Red Bean-Galls on White Willow. Actually, our form is a Golden or Orange-stemmed Willow, Salix alba 'vitellina'. The galls came with the willow, and in spite of a fairly heavy and continuing infestation of Red-Bean Sawfly, the 2’ potted willow we planted 6 years ago is now about 20’ tall, shading out a good portion of our backyard, and has to be constantly chopped back, away from the telephone line into the house. If the sawfly (and the chopping) has had any effect on this monster’s growth, then we haven’t noticed it). I suppose this sawfly is another accidental introduction into North America and it also has been introduced into Australia and New Zealand. One variety of its host, Salix alba 'Caerulea', is called Cricket-bat Willow, so the Aussies and Kiwis may have a better handle on any damage this sawfly may do.

 The larvae of the Willow Red-Bean Gall Sawfly are grub-like and feed in a gallery inside the bean gall. The gall can be anything from pale to green to red (usually most intense on the upper side of the leaf). The adults are small black sawflies – we have pictures of lots of these that are not identifiable, but we offer one that may look more or less like the adult (remember, take any identification based solely on a picture with a grain of salt).

 *Tommi Nyman, Alex Widmer, & Heikki Roininen. Evolution of Gall Morphology and Host-Plant Relationships in Willow-Feeding Sawflies (Hymenoptera: Tenthredinidae). Evolution 54(2), 2000, pp. 526–533

Sawfly Sunday: Slugs on the Cherry

In Alberta in the summer it seems a new sawfly is always just awaiting a few moments of spare time to claim one’s attention. I use ‘sawfly’ in the general sense – this week’s offering is in the larval stage. We don’t call caterpillars butterflies, but for some reason ‘sawfly’ usually seems to do for both adults and larvae. Not always though, there are such things as currantworms and then there is the Pear Slug Caliroa cerasi L.

 The University of Alberta’s Strickland Entomological Museum has an excellent write-up on the “Pear slug (official), Cherry slug, Cherry sawfly”, but no explanation for the ‘official’ common name. Considering that Linnaeus named the species ‘cerasi’, one would assume it was collected from the sour cherry Prunus cerasus (also named by Linnaeus), it being unlikely that the cherry was named for the slug (‘cerasus’ is Latin for cherry). As for the generic name, I am at a loss. ‘Cal-‘ in Greek means beautiful and ‘cali-‘ in Latin a wine cup, neither of which seems reasonable for a cherry slug unless Linnaeus had too much wine before coining the name. Come to think of it, ‘slug’ is used for a drink in English and the word seems to derive from the  Scandinavian  ‘slogga’. Perhaps Linnaeus was having a pun or two after a bit too much cherry wine, but ‘roa’ has triumphed over my etymological skills and imagination. Or perhaps 'Caliroa' refers to beautiful roses, another host. 

 The adult of the Cherry Slug is a small black sawfly that may or may not have been digitally captured in the Home Bug Garden – we have pictures of several nameless small, black sawflies. Like the sour cherry, the Cherry Slug is a relatively recent introduction to North America and like some other invaders, e.g. the Creeping Jenny Sawfly, the males seem to have been left behind. Most evolutionary biologists, at least those of the vertebrate ilk, are more than a bit uncomfortable with asexual reproduction (parthenogenesis). It just doesn’t seem right to them and they have invented numerous theories to prove that it should not exist, or if it exists it should die out, or if it doesn’t die out then it should be limited to out-of-the-way places no sexual species would waste their time on. Unfortunately for their theories, parthenogenesis is common in many invertebrates. In fact, all of the Hymenoptera, the order that includes the sawflies, are at least partially parthenogenetic – males are produced without sex and usually have only half a set of maternal chromosomes in their cells.

 The Cherry Slug can cause economic losses in pear and cherry, and is capable of feeding on numerous other members of the Rosaceae (including saskatoons). The second generation seems to do the most damage, but in Alberta only one generation a year is thought to occur. I guess that is why I don’t mind the Cherry Slug – there aren’t many of them and birds, especially those bloody House Sparrows, do more damage to my cherry crop than a few slug sawflies. There’s one advantage of a short summer: fewer pests to worry about.

Sawfly Sunday: What happened to my Saskatoons?

Ever wondered what happened to those Saskatoon berries with the little holes in their side? Well, chances are they were ruined by yet another in the myriad of sawflies that help gobble-up your garden. Several species of Hoplocampa sawfly (Tenthridinidae) including H. alpestris Rohwer, H. bioculata Rohwer, and H. pallipes MacGillivray, have been reported from saskatoons, but the only recent study I could find in the general neighbourhood of Alberta (fittingly from University of Saskatchewan in Saskatoon) was on a species that is supposed to feed on Choke Cherry (Prunus virginiana).

R.G. St. Pierre' and D.M. Lehmkuhl. 1990. Phenology of Hoplocampa montanicola Rohwer (Tenthredinidae) and Anthonomus quadrigibbus Say (Curculionidae) on their host plant Amelanchier alnifolza Nutt. (Rosaceae) in Saskatchewan Can. Ent. 122: 901-906.

St Pierre & Lehmkuhl report that adult sawflies emerged in mid-May prior to the period of peak flowering, fed and fooled around in the flowers, and laid one egg per flower during the period of petal drop in late-May. Larvae fed on about 2 fruit per infructescence and completed development by the end of June, just as the first saskatoons were beginning to ripen. The first fruit attacked was usually dropped, but the second was often retained on the shrub as a hollow shell. Larvae overwintered in the leaf litter. Almost half the fruit were ruined at one study site and I have noted similar levels of loss on my saskatoons. Whatever this species of Hoplocampa is, it is rather pretty, but on the whole I would rather have more saskatoons and fewer sawflies.

Sunday Sawfly: The Saw in Sawfly

Last Winter seems to have knocked back several of the sawfly denizens of the Home Bug Garden. The Imported Currant worm that usually devastates my red currant has been nowhere to be seen and the Willow Gall Sawfly is much reduced over previous years. I intend to post on these critters on future Sundays (using pictures from previous years), but today I thought I should explain why these relatives of bees, ants, and wasps with a caterpillar-like larval stage are called sawflies.

Unlike many ‘common names’, ‘sawfly’ seems pretty straightforward: a fly with a saw or a fly that saws. ‘Saw’ has a good Old Norse-Old English origin, and has been used for saw-like structures on animals at least since the mid-1700s according to the OED (1993 New Shorter version). ‘Fly’ is another good Old English word for any insect that flies. So, presumably some old English person put two and two together and got sawfly. Calling anything but a two-winged dipterous fly a fly really bugs entomologists, but Entomology itself is rather new to English, arriving from France in the mid-1800s according to the OED, long after fly was in general and indiscriminate use.

So, maybe ‘sawfly’ was an old English common name for sawflies, but I’m skeptical. The saw in a sawfly is the ovipositor (‘egg’ + ‘placer’), i.e. the egg-laying organ of an insect, in this case one with two pairs of membranous wings (Hymenoptera). We are most familiar with the hymenopteran ovipositor in the form it often takes in the Aculeata (bees, wasps, ants), a sting. However, the ovipositor may be very conspicuous in other hymenopterons, e.g. the ichneumonid fly, I mean wasp, that Adrian at The Bug Whisperer so beautifully captured a few months ago. One wonders why these are not called drillflies (or share the rude common name that foresters often apply to horntails [Siricidae] that confuses female oviposition into a stump with male sperm transfer).

In any case, sawflies have an ovipositor with a pair of blades that usually have a serrate lower edge and are used to saw a slit and deposit an egg into plant tissue. However, when not in use, sawflies withdraw their saws into the body, the saws are not very large to begin with, and seeing those saw teeth (which one may have to count for a species identification) is easy only under high magnification. So, my hypothesis is that some entomologist dreamed up ‘sawfly’ as a common name. Alas, my New Shorter OED is only the two giant volume edition that I could afford as a young professor and it has no information on the first usage of ‘sawfly’ (nor does the online OED). If I can hold out until 2037, the estimated date for the completion of the 3^rd Edition of the full OED, then perhaps I can totter into some library and harass the librarian (presumably a robot by this time) into checking for me.

Just as an aside, not all the HBG sawflies had a hard winter and the loosestrife sawfly is again eating all my Creeping Jenny. On 16 July this year I caught an attractive black and orange adult sawfly in the back yard and induced it to make the supreme sacrifice for science - drown in alcohol. This is the very first sawfly that I've run through all the keys to a species identification: Monostegia abdominalis, the ravager of my one remaining loosestrife, Creeping Jenny. A picture of its saw is above. Unfortunately, we don't have any pictures of the entire adult (they tend to shrivel-up when removed from the alcohol, as do many entomologists), but Molly Jacobson caught a good snap of one in New Hampshire this May and posted it on BugGuide. My adult was crammed with eggs. So, it may be that this species is bivoltine in Alberta, as in Quebec - see previous post for more details. However, given how late the Spring was (snow at the end of May), perhaps she just woke up late from her winter hibernation.

Sawfly Sunday: Double Mystery

I'm between field trips and time is short (and soggy - the weather has not been cooperating), so for this quick and late at night Sunday Sawfly I offer one on its way to being a bird dropping.  For those of us who have seen valued plants becoming sawflies of questionable value, this picture snapped in late August 2007 in a lilac bush in my back yard may offer some cheer. But I offer it as a test - who can identify the bird and, far greater challenge, any guesses on the unfortunate sawfly?

Sawfly Sunday: The Creepy Loosestrife Sawfly

I never would have expected it, but I have become quite obsessed with sawflies – those strange relatives of wasps and bees that cannot sting, have a saw-like ovipositor, have no wasp waist, and whose larvae look like caterpillars and mostly eat plants. In the Home Bug Garden, they seem to be determined to eat everything and are usually somewhere between interesting and devastating. Ergo, I am initiating a new tradition in the HBG: Sawfly Sunday. Now, what with the new Wildflower Wednesday, working full time, taking care of two gardens, and generally getting old and decrepit, I don’t expect every Sunday will have a sawfly posting, but my wife has collected quite a rogue’s gallery of creepy caterpillars not, and damaged plants. So here is the inaugural issue.

Monostegia abdominalis feeds on plants in the Primrose Family (Primulaceae) including loosestrifes (Lysimachia) and pimpernel (Anagallis arvensis) and was first described from Europe by Johann Fabricius (probably Linneaus’ most famous bug student). Actually, I should say plants that I was taught belong to the primrose family – apparently there are molecules that suggest these two genera would be better placed in the Myrsinaceae along with cyclamen – but in any case Linneaus described both plant species so we have a very tight origin of names here.

In Canada, our probable alien invader sawfly was first recorded on the introduced and naturalized garden plant Creeping Jenny (Lysimachia nummularia) around Ottawa and Montreal in 1965. In 1970, Peter W. Price – the famed insect ecologist who seems to have spent some time with the Forestry Research Lab in Quebec during his migrations from the UK to the USA – published a very nice study (Canadian Entomologist 102: 491-495) of our – lets call it the Creepy Loosestrife Sawfly – devastating a once unusually successful colony of the native Lysimachia terrestris around the frequently flooded margins of Caousacouta Lake in Quebec.

Now one might think that a loosestrife with the species name terrestris was more terrestrial than most, but it seems to be like most loosestrifes – they like boggy ground around water. Like most loosestrifes that I am familiar with, it has yellow flowers, so the common name Yellow Loosestrife is a bit useless. Swamp Candles is another common name and seems more evocative – especially if we want to build up some outrage that it is being eaten alive by an alien insect. However, the unusual success of Swamp Candles at  Caousacouta Lake was due to artificial flooding by the local hydroelectric company creating an excess of suitable habitat. Without the flooding, the plant might well have been too uncommon to notice it being defoliated – and perhaps would not have been colonized by our Creepy Loosestrife Sawfly to begin with.

Peter Price’s paper has an excellent overview of the life history of the sawfly and its interactions with the native loosestrife. The sawfly had, more or less, two generations a year – but some larvae in the first generation hedge their bets and decide to wait until the next year to emerge from their underground pupation chambers. The second generation started in August in Quebec, but I suspect there is only time for one generation here in Alberta. Males are extremely uncommon and Peter suggested that our Creepy sawfly is thelytokous – that is females do not mate, but reproduce parthenogenetically. The females live only a few weeks but mature 30-70 eggs that they have available for sawing into the upper surface of the leaves of the loosestrife. The larvae will drop off the leaves if disturbed (I can vouch for that) and consume a tremendous amount of plant material (I can also vouch for that) – so much so that the loosestrife is mostly defoliated and many plants die. Or at least that is what was happening 40-odd years ago – I wonder what is happening at Caousacouta Lake now? Did the sawflies eat all the loosestrife and go locally extinct? Was the hydroelectric company forced to stop flooding the lake – what would that do to the dynamics? Has the loosestrife evolved resistance to the sawfly? One wonders if this isn’t an interesting historical entomology study waiting to happen.

Setting aside my minimal angst at the decimation of my Creeping Jenny (it was a free gift from Adrian, did far too well for the first couple of years, and now I don’t seem to need to worry about it becoming weedy), I do have a bit of worry about the sawfly’s ability to colonize native species. Dave Smith – the North American sawfly guru at the USDA with about 250 publications on sawflies - has a pdf plate on the web showing the adult, pupa and late instar larva and damage to the native fringed loosestrife. The fringed loosestrife (Lysimachia ciliata) is one of two loosestrife species that live around the lake at our place in the country (the other is Tufted Loosestrife Lysimachia thyrsiflora). They aren’t very common, so perhaps they are relatively safe – unless someone starts a loosestrife farm nearby and the overflow of Creepy sawflies eats them out. Also, I wonder if the sawfly isn’t the reason my expensive Variegated Golden Alexanders (Lysimachia punctata ‘Alexander’) disappeared from my bog garden. Hmm, just checked my notes and I’ll be buggered if it doesn’t say “cocked it Winter 2007-08, after sawfly defoliation 2007”. Bloody sawflies!