Saturday, September 19, 2009

Frog spit & colour morphs: Pseudodiversity & other false ideas

Frog spit and spittlebugs are one of those childhood memories that now evoke mixed feelings. Did I really eagerly plunge finger tips into poop and plant-sap spittle and react with joy when uncovering a frothing froghopper nymph?

Well, that’s how I remember it, but now things are different. Spittlebugs (true bugs: Order Hemiptera, Family Cercopidae) or froghoppers (as the adults are called) are interesting insects for any number of reasons. One of the primary is, of course, the protective envelope of bubbles that the nymphs generate around them as they feed. That’s cool, even if you aren’t a kid, but once you know that the bug anus is intimately involved, one is apt to get a bit skittish (NB – always wash your hands after playing with spittlebugs). Adult fastidiousness aside, the most likely spittlebug one is apt to encounter is two things you don’t want in a garden bug: polyphagous and exotic. Another way to say this is ‘an alien that eats everything’.

Summer before this, we had quite the explosion of just such a spitting machine in the Home Bug Garden: Meadow Spittlebugs (Philaenus spumarius). Bellflowers, globe flowers, Queen-of-the-Prairie, goldenrod, aster, yarrow, and many other cherished garden gems had hunks of spit sitting just below the flower buds – wilting the buds and terminating the flowers. Hundreds of soapy squirts and weeks of spit and green ocher stained finger tips later, the spit population appeared undiminished. It was enough to drive a knee-jerk environmentalist to the evils of synthetic insecticides – if only such a synthetic chemical alternative were available! Alas a history of insecticide abuse, and the inability of government to favour science over fervour, has left the home gardener with little to do other than pray for parasitoids. Unfortunately, spit and parasitoids don’t seem to mix.

Not that I am entirely the innocent victim in this outbreak. I suspect the main reason for our spit-drenched garden was that I left most of my perennial plant stems standing over winter. I could claim that I did this for aesthetic reasons (winter interest), horticultural reasons (plant tops trap snow and help plants to overwinter), or just plain knee-jerk environmentalism (it is natural for plant tops to last over the winter and cutting them down would be unnatural and wrong). Truth be told, being a lazy bugger (aka ‘overworked’) conspired with all of the before to let the tops stand. Unfortunately, it is inside the stems of perennial plants that the froghopper secrete their eggs – the eggs that turn into spit and dead flowers the next Spring.

This last year I cut down and composted my perennial tops before Spring had sprung. Leaving them up most of the winter looked good and trapped snow, and cutting them down before it got warm seems to have kept the spittlebugs down to squishable levels. Other insect pests and diseases also overwinter in plant tops, so ‘better late than never’ applies here. The only downside to this approach is that fewer spittlebugs means even fewer froghoppers – and the Meadow ‘Froghopper’ is a really interesting animal, if only because it looks like dozens of different species.

Bugguide Net has a great poster displaying some of the diversity of colour morphs found in this single species and this posting displays a few of the variants found in the HBG. It is a bit disappointing that we have so few froghopper species (only two, including the unidentified spittlebug on our birch), but the Meadow Spittlebug is a good reminder of the pitfalls of using skin colour as a guide in life. No matter what the colour on the surface, a miscreant may lie below.

Sunday, September 6, 2009

Biodiversity Gone Good: Our Friendly Wasps

Friendly?, well, I exaggerate a bit, but after the last posting on evil hornets, I thought I should exonerate all those wasps (Order Hymenoptera) that wouldn’t hurt us unless we really, really were asking for it. These are the so-called ‘solitary wasps’ – and in going it alone is their secret for getting along with us. Actually, I probably have that backwards: we tend to get along with solitary wasps because they can’t, and have no reason to,  gang up on us.

Like their freedom loving relatives, the ‘eusocial’ ('good', but actually bad, social) yellowjackets and hornets start out as solitary wasps each Spring when queens do all the normal wasp work themselves – find their own food, find a site for a nest, build the nest, lay the eggs, protect the nest, and feed their offspring until they are ready to pupate and become adults. Sounds all very noble and hard-working, but in reality queen yellowjackets and hornets aren’t adverse to stealing another queen’s nest and murdering the owner. In either case, the noble queen or insidious usurper rears grubs that develop into a worker cast – an army of so-called ‘non-reproductive’ or ‘sterile’ sisters (actually ‘suppressed’ would be a more accurate adjective, since workers may reproduce) that do all the work from then on and all the stinging.

These eusocial wasps have modifications in behaviour, chemicals, and stinging apparatus that have evolved to help defend large nests full of their sisters, half sisters (assuming their moms aren't monogamous), and drones. In fact, they have to defend that nest, since the chance of being able to found a new one is probably slim (and perhaps also the reason that stealing nests is common). Unfortunately, when they defend the nest against us, we suffer. Wasps that haven't become social, however, are much less aggressive. So, cheers for the solitary wasps!

Solitary wasps come in two forms: the hyperdiverse parasitic wasps (Ichneumonoidea and more) and the hunting wasps that are close relatives of the eusocial bees and wasps (and ants). Each female hunting wasp must build their nest(s) alone (males just dangle around), so the nests are small, and there is no other wasp to come to its aid if it is attacked. If fact, in spite of all the care and attention a hunting wasp mom will devote to rearing its offspring, it will never see them as adults and has no hope of recruiting them to defend a nest.

Thus, overly aggressive hunting wasps would tend to come to a bad end, but those with a more philosophical attitude, can move on, start another nest, and send daughters and sons into the next generation. That doesn’t mean they won’t put up a bit of a fight, many are capable of delivering a painful sting, but in general they aren’t going to slug it out with something as large as a human. It also helps that solitary wasps are only really interested in hunting down spiders or insects to feed their grubs and an occasional sip of nectar at a flower to keep them going. When a solitary wasp finds you at a picnic, it is most likely because you have attracted flies (which many take as prey) or you have put your blanket over their nest in the ground and they can’t find their way home. Some solitary wasps are members of the Vespidae, the home of hornets and yellowjackets, or close relatives like the mostly black spider hunting wasps in the Pompilidae, but most belong to other families.

When I was a kid and got to read excellent books like Wasp Farm by Howard Ensign Evans (sadly, now out of print - but try the library), the non-vespine hunting wasps all fit in one family, the Sphecidae. Now, alas, most of my bug reading is condemned to papers in scientific journals where any delight has been rigorously suppressed and the information is highly refined - like white sugar, but without the sweetness. Oh well, “Gracefully surrender the things of youth” and that includes a monolithic Sphecidae. The current hypothesis includes three families, and the one we definitely have in the Home Bug Garden, the Crabronidae are considered the sister group to the bees and only more distantly related to other hunting wasps. They do look a bit like bees, but go about their business stuffing flies, caterpillars, bark lice, or the like into their nests instead of pollen and honey. The Crabronidae has some giants, the Cicada Killer (Sphecius speciosus) being perhaps the most famous, but the largest I have seen in the HBG is about an inch long Bembix americana. This wasp nests in sand and feeds her grubs fly after paralyzed fly. I’m not sure what she was doing on a goldenrod in a yard surrounded by oppressive clay soils as far as the eye can see – but she now sits on a pin in a museum. I don’t have any pictures, but my friend The Bug Whisperer has an excellent shot of another, more fortunate, B. americana feeding at an aster.

Most solitary wasps, however, limit their parental care to choosing a host and ovipositing an egg. No nests are involved. These parasitic, or better, parasitoid wasps have no nest to defend, and their egg laying organ, the ovipositor (i.e. egg placer), is used to lay eggs in or on their prey, not to sting annoying humans. 'Parasitoid' is preferred in scientific circles because the end result is almost always a dead bug (whereas a parasite is happier when you keep on living – think head louse). Check out the aphid mummy above perving the mating Ancistrocerus parietum – it may look like an aphid, but it is just a hollow shell with a parasitoid wasp grub inside, undoubtedly a tiny member of the Ichneumonoidea (Ichneumonidae, Braconidae). Although I find hunting wasps more interesting,  it is the parasitoids that make up most of the - unidentified - species diversity of wasps in the HBG.

As far as we are concerned, parasitoid wasps are usually entirely good, except they are difficult to identify and their prey can expect a gruesome end – being eaten alive. That, however, is the fate of the prey of all wasps, including the paralyzed prey of hunting wasps or the mashed up prey of the social vespids. Well, if you want to nitpick, I guess hornets just cut-up insects alive, sort of like Dexter, and then feed the mashed bits to their grubs: nature ocher in sting and mandible. As long as the victim is an insect, though, do we really care?