Sunday, August 22, 2010

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

Thursday, August 19, 2010

Wildflower Wednesday: Pygmyflower Rockjasmine

Also known as Northern Rock Jasmine and Fairy Candelabra, Androsace septentrionalis L., a member of the Primrose family, must be one of the tiniest wildflowers in the Home Bug Garden. One wonders how this diminutive annual plant - the leaves are only about an inch (25 mm) long and the flowers perhaps 5 mm in diameter - has acquired so many elaborate common names? However, with a hand lens or a macro lens, the charms are undeniable. Our Fairy Candelabras have been few and far between, mostly transient in disturbed soil (it is a good competitor against spring row crop seedlings, and hence considered a weed). The flowering scapes have never gotten more than a few centimeters tall in the HBG, but apparently they can reach 25 cm (10 inches), so that would make them a bit more obvious. Also, Fairy Candelabra has a circumboreal distribution and seems to be a common member of alpine and subalpine plant communities, so it appears in many research papers (although rarely as the star, mostly just the pretty wall flower). I've picked it because we like it and its brevity is appropriate for another late post due to too little time.

Monday, August 16, 2010

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.

Thursday, August 12, 2010

Wildflower Wednesday: Broken Rocks, Mountain Grass & Truthful Deceit

Some readers may have noted that my concept of the day of the week seems to be drifting. Too much work and not enough time is part of the drift, but even more extenuating is the inherent complexity of Nature. For example, this week I intended to post on some of my wild “rock-breakers” (not Adrian’s admirable images of Red Rock Coulee - but saxifrages) only to find that my first choice Parnassia palustris L. - Marsh Grass-of-Parnassus – although crammed into the Saxifragaceae in 1930, never really fit. Indeed, most of my reference books place Grass-of-Parnassus in its own family, Parnassiaceae (this name dating from 1821). More recent molecular work, however, places the two genera of Parnassiaceae in a clade that includes the Madagascar-Comoro Islands endemic genus Brexia (which at least has 5-parted flowers that resemble Parnassia) and the Celastraceae, a family of woody plants, perhaps familiar to some from ornamental shrubs in the genus Euonymus (Burning Bush) or the bittersweet vines (Celastrus species including the highly invasive Oriental Staff Vine, C. orbicularis),
 Several conundrums also inhabit the common name: Marsh Grass-of-Parnassus. Although it starts out well – this circumboreal species grows in cool, wet soils and the species name palustris is Latin for boggy or marshy – the Grass and Parnassus are not immediately self-explanatory. Mt Parnassus is a hunk of limestone that rises to 2,457 m (8,062 ft) between the 38th and 39th parallel in Greece, a land not known for an arctic climate nor an abundance of water. Linnaeus named Parnassia for the mountain, and the plant is supposed to like calcareous soils, but the slopes are unlikely to have been covered with Grass-of-Parnassus. Perhaps, at least in antiquity, Mt Parnassus had lots of boggy meadows and springs. And in antiquity, I think, lies the grass conundrum. Although a modern grass should reside in the Graminaceae (or if you prefer, Poaceae) along with corn, wheat, rice, barley, oats, and a weed-free lawn, according to the OED the basic meaning is nowhere near so phylogenetically precise. The first definition of ‘grass’ is of low herbage eaten by livestock and ‘Gramineae' doesn’t rate a mention until definition 4b (ahead of the fumitory usage at 7).
 Continuing with the antiquity theme, Mt Parnassus was reputed to be the home of the Muses: the water nymphs credited with inspiring poetry, literature, and learning. They were protected by Apollo and associated with the springs of Helicon and Pieris (perhaps good places for Grass-of-Parnassus to grow). This is entomologically interesting because Heliconius (as opposed to Heliconia, a genus of plants) and Pieris are genera of butterflies (the former including many colourful but mostly tropical butterflies, and the latter the Cabbage White). Parnassius is also a genus of butterflies that includes the Mountain Apollo, P. apollo. Butterflies, however, do not seem to be attracted to Grass-of-Parnassus, which is reputed to be pollinated primarily by flies. And there’s another fly in the ointment: conflicting information about pollination in Parnassia. Some sources claim the plant fools its flies with fake rewards and some that it provides nectar. Some claim that it is outcrossing, others that the anthers dump pollen directly on the stigma. Based on a study by Sandvik and Totland (2003, Can. J. Bot. 81: 49–56) of two populations of P. palustris in Norway, these conflicting claims all have some merit.
 Parnassia flowers are 2-3 cm in diamter and its floral parts are in whorls of 5: calyces, petals, and anthers. It is protandrous, i.e. male first – the anthers usually mature and release their pollen before the ovary is receptive. This promotes outcrossing and Sandvik and Totland found outcrossing dominant in one of their populations, but not in the other. Flies were the primary pollinators, although the species differed between populations, and these results are consistent with other studies. Hoverfies (Syrphidae, e.g. Sphaerophoria, Eristalis) are of especial importance, but members of the Tephritidae, Muscidae, Dolichopodidae, Anthomyiidae, Phoridae, and Empididae also have a role to play in various parts of the World.
 As well as the usual fertile anthers that produce the pollen, however, Parnassia also has sterile anthers, called staminodes, that are divided into thin rays with shiny, rounded knobs at the tips that resemble nectaries, but do not produce nectar. These false nectaries do fool inexperienced flies, but two real nectaries are present below each cluster of rays that produce both nectar and a honey-like scent. When staminodes were experimentally removed from flowers, Sandvik and Totland found that flower visitation rates were less than half of that in intact flowers, flies spent little time in flowers without nectaries, and seed set was poor. So, rather than cheating its pollinators, the staminodes simply mislead them, a harmless bit of hyperbole that makes the flowers seem more attractive from a distance (although one supposes that there may be flies that never figure it out).

In Europe, Grass-of-Parnassus is considered a harbinger of Autumn and, along with the Muses, has inspired at least one book with a less than elevated view of the plant: “It may be as well to repeat in prose, what has already been said in verse, that Grass of Parnassus, the pretty Autumn flower, grows at the foot of the Muses’ Hill, and other hills, not at the top by any means.” (Grass of Parnassus - Rhymes New and Old by Andrew Lang 2nd Edition 1889). In short-summer Alberta, the last tulip is not that far off from autumn, but Grass-of-Parnassus starts blooming in July, and I rely more on the goldenrod that starts a few weeks later for depressing reminders of the coming first frost.

Marsh (also called Northern) Grass-of-Parnassus needs wet soil, so it likes my bog garden, and does well in sun to light shade. Most sources list this circumboreal herbaceous perennial as hardy only to USDA Zone 3, but the plant occurs throughout Alberta in much harsher zones, so I would expect it to survive at least to Zone 2. In North America, it is distributed from Alaska to Labrador ranging south to Oregon, Wyoming, North and South Dakota, the Upper Great Lakes region, and New York, and further south in the western mountains. It is considered rare in South Dakota, Wisconsin, and New York. Gardens North has seed available of both the eastern relative, Parnassia glauca, and P. palustris (seed collected in Alberta) - and lists the latter as hardy to Zone 2.

Monday, August 9, 2010

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.

Wednesday, August 4, 2010

Wildflower Wednesday: Showy Aster

I consider Showy Aster my most successful garden wildflower experiment. The original planting has formed a thick clump about a metre across, a half a metre wide, and 1.2m tall in a shady corridor between a sidewalk and a fence. The tops are covered with good-sized purple-rayed asters with yellow centres from late July. It is a bit floppy in the shade, so requires some support to keep the sidewalk clear, and every now and then a rhizome pops up a shoot in the bed – but they are easily transplanted. The transplants have taken in the front yard in dappled shade and fit right into the woodland theme. The flowers are attractive to butterflies and bees, it does well in both sun and in shade, it is extremely hardy (at least to Zone 2), and it makes a nice link between the Home Bug Garden and the countryside, where it is now a conspicuous adornment. The Edmonton Naturalization Group agrees.
About the only problem with Showy Aster is that it is no longer a ‘star’. Actually, there isn’t much left in the ‘native’ North American Flora that glimmers as a true Aster, except Alpine Aster. Showy Aster, and many others, have been moved to the genus Eurybia and to accommodate the change in generic gender, the male Aster conspicuus (Showy Star) has become the female Eurybia conspicua (Egregious Eurybia?). Since the flowers are hermaphrodites, I don’t suppose they are too impressed with the change. Nor am I, especially since a heap of other former Aster have been moved into the neuter genus Symphyotrichum. So, Lindley’s Aster (attractive when healthy, but unfortunately susceptible to both aphids and mildew) has moved from Aster ciliolatus to Symphyotrichum ciliolatum (and been mostly weeded out of the Home Bug Garden).
In contrast, Smooth Aster, the late Aster laevis, now Symphyotrichum laeve (which the spellchecker keeps changing to ‘leave’) is quite a nice garden plant. It isn’t as showy as Showy Aster, but makes a nice, understated contrast and blooms around the same time. Unfortuantely, Smooth Aster likes the open, lots of sun, and generally drier conditions. So it persists only on the margins of the Home Bug Garden.
 Compared to Symphyotrichum (which probably means ‘grown together hairs’, I would guess in reference to some peculiarity of the pappus), Eurybia is an attractive name. I like to think that Alexandre de Cassini in 1820 used the name in reference to the Eurybia of Greek Mythology – consort of a Titan and a daughter of the Earth and the Sea. Wikipedia, however, speculates that it is from the Greek words for ‘wide’ and ‘few’ and refers to the few and broad ray flowers. Since Showy Aster has numerous narrow ray flowers this seems dubious. In any case, Eurybia is also a genus of metalmark butterflies, and so another Zoo-Bot homonym that should add to the confusion.
The confusion in names doesn’t matter to the butterflies that visit the asters, except perhaps to some. The Pearly Crescent (Phyciodes tharos) is known to feed on ‘asters’ in the obsolete sense, and the Northern Crescent (Phyciodes cocyta) is known to  feed on Symphyotrichum laeve in Colorado. Apparent there is little or no data on what the caterpillars feed on in Alberta, but one or the other of these Crescents (the species are very similar and overlap in range here) was showing quite an interest in Eurybia conspicua this weekend. It would be interesting if the Crescents were discriminating about Eurybia and Symphyotrichum.

Sunday, August 1, 2010

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 3rd 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.