Wednesday, June 29, 2016

More Drama at the Bee Block

I was going to write at some point about how one of the other benefits of putting up a bee block ("bee condo") for solitary bees and wasps is that their parasites have a harder time finding them there than in a more natural situation. Well, last week I was proven completely wrong about that. On the positive side, I identified two new tenants in the block in our backyard.

Female mason bee, Heriades sp., on milkweed, before I had identified it

Early in the week I happened to see an insect fly from one of our blooming milkweed plants and literally make a bee line into one of the smaller holes in our bee block. I was not able to make an identification, so swiftly did it disappear.

Stakeout: female Sapygid wasp patiently eyeing potential hosts

Friday, June 24, I happened to glance at the bee block and noticed a very slender insect in one of the corners. I broke out the camera, took a couple pictures, and identified it as a sapygid wasp, family Sapygidae. Sapygids are parasitic on bees in the families Megachilidae and Apidae, and mason wasps in the family Vespidae, subfamily Eumeninae. The larvae of the sapygids either feed on the food stored for the host's offspring, or live as ectoparasites on the host larvae. Great.

Territorial dispute? Another sapygid joins the first one

Oh, here comes *another* sapygid. There were two on the nest block for only a brief time, and though it is not easy to separate the genders, I had no way of telling if it was a pair, or I believe they were two competing females. Males have even longer antennae and a blunter tip to the abdomen.

While photographing one of the sapygids, I got lucky. One of my pictures captured the mystery lodger in the bee block from earlier in the week.

Target detected: Sapygid wasp spies Heriades mason bee giving away its nest location

The insect coming to one of the smallest diameter holes is a type of mason bee in the genus Heriades. There are only eleven species of Heriades in North America north of Mexico, and five species in Colorado. Only Heriades cressoni has been officially recorded in El Paso County, but our bee block resident could still be one of the other species.

The female bee uses a pre-existing tunnel, such as an old beetle boring in a dead tree or log, or a hollow twig, in which to make her nest. She creates a series of cells with a partition of plant resin dividing one from another. She usually leaves one empty cell at the entrance before sealing the completed nest with a resin plug. Should a parasite break in, it might be duped into thinking the nest was empty; or at least dissuaded from having to break through a second "door."

Female Heriades sp. mason bee collecting pollen beneath her abdomen

The mother bee gathers pollen with a brush of hairs on the underside of her abdomen. Back at the nest she mixes the pollen with nectar she regurgitates from her crop (an internal food storage organ). This is "bee bread" that she fashions into a ball or "loaf" for each cell. She then lays an egg in the cell, and finally seals it with the resin partition. She repeats this scenario until the nest cavity is filled.

The sapygid wasp that had been waiting patiently for just the right moment to lay her own eggs in the bee nest finally made her move. She quickly backed halfway into the hole on the bee block and presumably deposited one or more eggs before fleeing the scene. This is the strategy that many, if not most, bee parasites use. They stake out a nest in the process of being provisioned, and enter when the host bee leaves to gather more nectar and pollen, or material used in making a partition between cells.

Game on! Female sapygid wasp laying eggs in Heriades mason bee nest

Another surprise happened when I saw a mason wasp approach and then enter another hole on the block. This one is different from the one I wrote about a couple weeks ago. It is smaller and more ornately patterned. It is either Parancistrocerus sp. or Stenodynerus sp. One cannot tell the two apart from images of live specimens in most cases. Even with actual specimens under a microscope it is difficult to make an identification. Like most cavity-nesting mason wasps, paralyzed caterpillars will serve as food for the larval offspring.

Female mason wasp, Parancistrocerus sp. or Stenodynerus sp.

I can hardly wait to see what comes next to our bee apartment building. Please comment if you yourself have a bee block (or more than one), and share what is coming and going from it, what parasites or predators you have seen lurking, and any other pertinent observations.

Sources: Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press. 570 pp.
Scott, Virginia L., John S. Ascher, Terry Griswold, and C├ęsar R. Nufio. 2011. "The Bees of Colorado (Hymenoptera: Apoidea: Anthophila)," Natural History Inventory of Colorado No. 23, University of Colorado Museum of Natural History, Boulder, Colorado. 112 pp.
Scott, Virginia. 2015. "Resin Plugs (part 1) and Their Bugs," The Bees' Needs Blog.

Saturday, June 25, 2016

Beetle Bonanza

Back on June 13, while my wife and I were headed to a different destination, we passed by a logging mill operation in Black Forest, northeast of Colorado Springs. I wanted to go back another time, and did so on my own this past Thursday, June23, but not without much trial and error. It was a rewarding outing once I got there, with beetles of all kinds flocking to the freshly-cut Ponderosa Pine logs.

Jewel beetle, Chrysobothris dentipes

It turns out I had not been paying enough attention to the route we had taken the first time, and so on Thursday I became hopelessly lost. I phoned my wife and she informed me I was nowhere near the right road. Consequently, I got to the site in the late morning. When I arrived, there was no one to be seen. I looked around anyway, as there were also no postings against trespassing.

The first insects I saw were what I expected: medium-sized jewel beetles, Chrysobothris dentipes, as depicted above. These members of the family Buprestidae look exactly like little shards of pine bark, but they move often enough to be easily seen. Several males were engaging in "butt-thumping" displays to nearby females. Below is a very brief video depicting this. It is surprisingly audible, and also hilarious. I hope to go back again and get a longer video segment.

Also present were a fair number of the magnificent metallic green Phaenops gentilis. Though they are only about 8 millimeters in length, these buprestids are still conspicuous. Like most jewel beetles they are quick to fly when disturbed, though they usually simply run so erratically as to be nearly impossible to get an image of. Females pause often to lay eggs, though, so that is your one opportunity. The one below took time to groom itself and luckily I was in the right place at the right time.

Jewel beetle, Phaenops gentilis

While I was photographing another insect, I glanced down to see a very large buprestid that had landed on my shoulder. I grabbed it, and it turned out to be a Western Sculptured Pine Borer, Chalcophora angusticollis. Measuring 20-33 millimeters, they are among our largest jewel beetles. When they fly, the lifted elytra (wing covers) expose a bright blue, green, or violet abdomen. I brought it, and another specimen, home to photograph.

Western Sculptured Pine Borer

What surprised me most were the large numbers of predatory checkered beetles, family Cleridae, active hunters of bark beetles and other small insects. I thought that I was seeing one species, with individuals of varying sizes, but upon looking at my images it became apparent there were three species.

Checkered beetle, Enoclerus moestus

Enoclerus moestus was the first one I came across. E. lecontei was likewise common.

Checkered beetle, Enoclerus lecontei

Lastly, the largest species was the "Red-bellied Clerid," E. sphegeus. While the adult beetles will kill and consume a variety of other insects, the larvae appear to prey exclusively on bark beetle larvae. You know, like the Mountain Pine Beetle and its relatives that are often blamed for killing entire forests.

Red-bellied Clerid, Enoclerus sphegeus

Longhorned beetles were present on the log stacks as well. I expected the White-spotted Sawyer, Monochamus scutellatus, and indeed I found a couple of females, one of them ovipositing, and a single male. These are large beetles that live up to the longhorn name. Their antennae are exceptionally long, especially in the males.

Female White-spotted Sawyer laying eggs

The most abundant of the longhorns, though, were flower longhorns in the genus Grammoptera. I even found a pair mating.

Flower longhorned beetles, Grammoptera sp., mating

The freak of the longhorn show was the Ribbed Pine Borer, Rhagium inquisitor. The adults look very little like a typical longhorned beetle, having quite short antennae. Two specimens landed on me or in my vicinity.

Ribbed Pine Borer

They are medium-sized at 12-15 millimeters in body length. They get their name from the woven wreath-like ring consisting of coarse wood fibers that the larva creates for its pupal chamber.

I also found a few oddball beetles including a very tiny weevil, Lechriops californica. At least that is what I think it is. They bore, in the larval stage, under the bark on the trunk and larger branches of various pines.

Tiny weevil, Lechriops californica maybe

Another predatory beetle was a very small clown beetle, family Histeridae. It may belong to the genus Platysoma, which live under bark and hunt the larvae of flies and beetles.

Clown beetle, Platysoma sp.

There were non-beetle insects, too, of course. The most common were the syrphid fly Chalcosyrphus piger. Females were alighting on the logs, presumably to oviposit (lay eggs) there. The larvae of these flies feed on decaying wood, and perhaps fermenting sap.

Syrphid fly, Chalcosyrphus piger

The most exciting find was a female aulacid wasp, family Aulacidae, in the genus Pristaulacus. They are easily mistaken for ichneumon wasps at first glance, but the ovipositor is downcurved at the tip; and the abdomen is connected high on the back of the thorax. These wasps are more closely allied to ensign wasps (Evaniidae) and carrot wasps (Gasteruptiidae). They are parasites of wood-boring beetles, surprise, surprise.

Aulacid wasp, Pristaulacus sp.

I am looking forward to returning to this site, as long as I am welcome. Those towering stacks of big pine logs are a bit intimidating, I have to admit, but worth braving for the bounty of beetles.

Male longhorned beetle, Acanthocinus obliquus

Sources: Cowan, B.D. and W.P. Nagel. 1965. "Predators of the Douglas-Fir Beetle in Western Oregon," Technical Bulletin 86, Agricultural Experiment Station, Oregon State University, Corvallis, Oregon. 32 pp.
Furniss, R.L. and V.M. Carolin. 1977. Western Forest Insects. Miscellaneous Publication No. 1339, U.S. Department of Agriculture, Forest Service, Washington, DC. 654 pp.
Smith, David R. 1996. "Aulacidae (Hymenoptera) in the Mid-Atlantic States, with a Key to Species of Eastern North America," Proc. Entomol. Soc. Wash.. 98(2): 274-291.

Wednesday, June 22, 2016

A "Boring" Place to Nest

Last week I talked about the benefits of putting out bee blocks ("bee condos") for solitary bees and wasps to nest in. I thought it might help to understand why this is important in light of where these insects normally nest in nature.

Passaloecus aphid wasp near her nest hole

Dead, dying, and weakened trees are exploited by a number of different wood-boring beetles. The adult female beetles lay their eggs in bark crevices and the larvae that hatch then bore into the wood, feeding as they go. Eventually they enter the pupa stage near the surface of the wood. The adult beetle that emerges from the pupa then chews its way out. The result is a round or oval exit hole.

Solitary bees and wasps make use of these abandoned beetle borings. In fact, competition for the right size holes is keen. A wasp can modify the entrance to some degree by chewing-off wood fibers to expand the size, or plastering mud or resin to shrink the opening. That is a lot of effort, though, so wasps will look high and low for a hole that fits them perfectly.

A typical deathwatch beetle, family Ptinidae, that makes the holes that many wasps nest in

Among the most coveted of holes are those made by emerging deathwatch beetles in the family Ptinidae (formerly Anobiidae). These are tiny insects, and you might be hard-pressed to fit an entire pin or tack (head and all) into one of their perfectly round exit holes. Deathwatch beetles are also prolific, and so there will be many holes in a given dead tree. It may look like someone fired a load of buckshot into the bole.

A super-slender keyhole wasp, Trypoxylon sp., about to enter her hole

Last week I came across just such a tree, a cottonwood, that was teeming with wasps coming and going from various holes. I recognized at least three genera: Symmorphus mason wasps, Trypoxylon keyhole wasps, and Passaloecus aphid wasps. None measured more than about six millimeters. Mason wasps harvest caterpillars as food for their offspring. Keyhole wasps hunt spiders, and aphid wasps go after aphids. Some yellow-faced bees, also known as masked bees, genus Hylaeus, are also known to use such holes.

A cuckoo wasp, family Chrysididae, bides her time

Meanwhile, metallic green cuckoo wasps, family Chrysididae, and wild carrot wasps, family Gasteruptiidae, were looking for opportunities to lay their own eggs in the nests of the other wasps, at the expense of the host's offspring. Mostly, though, there was competition for nest holes, and male wasps harassing the females for mating opportunities. A male or two might jump on a female, and they would tumble off, leaving the door open for another female wasp to claim the nest hole.

Want to witness this action yourself? Look for dead, standing or half-fallen trees with bark stripped off, and usually in a shaded location or at least on the shady side of the tree itself. You might be surprised to see a wasp enter a hole head first, then exit the hole the same way. Somewhere inside there is enough room for the wasp to turn around.

A mason wasp, Symmorphus sp., checks out her potential new digs

You may have trouble finding dead trees, and this is why solitary wasps and bees need our help. Property owners, and even managers of natural parks, will cut down trees deemed a potential hazard, such that they can avoid potential liability issues including litigation should a tree fall on a person, vehicle, home, or other valuable object. The consequences of this include a housing shortage for everything from flying squirrels, woodpeckers, swallows, wrens, owls, and other birds, to solitary bees and wasps.

Please consider building or buying a simple, but quality, bee block and installing it somewhere on your property. You can find resources to do that in last week's blog post. Let me know what tenants you get as a result. We know precious little about most insects that are not considered economically important in a good or bad way, so all observations are important. Thank you.

Wednesday, June 15, 2016

The Mason Wasp Euodynerus foraminatus Endorses Bee Blocks

Those "bee blocks," chunks of wood with holes of varying diameters drilled into them, are all the rage now for attracting solitary native bees like leafcutter bees and mason bees. They do work, no matter where you live, and I have proof. Ok, so the first occupant in our newly-hung bee block is actually a wasp, but that is also a good thing, and I'll explain why.

A bee block need not be as fancy as the one shown here. There are some standards you should adhere to, though, and a thorough explanation is found here. Solitary bees come in a variety of sizes, so having a good selection of various diameter holes is helpful.

Why am I excited that a solitary wasp is using our block? Wasps are "flower visitors" that go to flowers strictly for nectar to fuel their activities (think gas station, not grocery store), but they do a fair bit of pollinating in the process. The biggest benefit of wasps, though, is that they are parasitoids of insects we consider pests.

The scenario for the mason wasp using our nest box, Euodynerus foraminatus, goes like this: The female wasp catches and paralyzes a caterpillar, and flies it back to the nest hole where she stashes the victim, and usually several more, as a larder of food for a single larva offspring. She lays an egg on the first or last victim, and then erects a mud partition. She repeats the steps, such that one of those holes you drilled might end up filled with several cells, each holding numerous caterpillars that won't be eating your garden plants. The preferred prey of E. foraminatus are larvae of moths in the families Oecophoridae, Tortricidae, Gelechiidae, Pyralidae, Crambidae (subfamily Pyraustinae). All of these include some notorious pests, as well as caterpillars that conceal themselves in rolled or tied leaves that other wasps won't go to the trouble of extracting.

We know at least one nest tunnel is complete because it has been plugged with mud. You can identify the different types of bees and wasps using a "bee condo" by the kinds of closures they make. Some megachilids (mason and leafcutter bees) will make the final closure with a plug of chewed-up leaves. Other bees will plug a nest hole with plant resins.

Besides the comings and goings of the bee block inhabitants, you can get some other kinds of drama. While watching the bee block for signs of activity last Friday, I noticed a crab spider hanging out under the "eave" on our bee block. Sure enough, when the wasp approached the spider reacted, hanging of the roof and opening its "arms" in a potentially lethal embrace. The wasp ignored or never noticed the threat, but I ushered the spider to another part of our yard anyway.

You may think that there is no way one of these boxes would work in your yard. The above image is of our yard, behind our townhouse unit. Look at it! It is literally like ten-by-twelve feet. Surely, if we can make this work, so can you. It takes virtually nothing to put one up, and it offers both critical bee real estate for the insects, and hours of entertainment for you and your family. Since solitary bees and wasps do not have vast quantities of offspring and honey stores to defend, they are not going to sting you. Besides, they are too busy working.

Back to that mason wasp for a second. Euodynerus foraminatus is a very widespread species, found coast to coast in the United States, plus all Canadian provinces, and down into Mexico, too. There is a very good chance you could attract one to your own bee block.

Sources

: Buck, M., Marshall, S.A. and Cheung D.K.B. 2008. "Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region," Canadian Journal of Arthropod Identification No. 5: 492 pp. (PDF version).
Stone, H.B. 2014. "Insects of the Week: Eumenids and Chrysidids," The Bees' Needs Blog.

Sunday, June 12, 2016

Jumping Spider, Phidippus insignarius

While exploring Cheyenne Mountain State Park on June 3, I caught glimpse of a very colorful jumping spider prowling a dead thistle stalk among some branches of scrub oak (Gambel's Oak). My first thought was it must be a male Phidippus of some kind, but I am used to them being a fair bit larger than this one was. Well, I was excited to find out later that it was indeed a male Phidippus insignarius.

The crazy thing is, I was already familiar with that species, thanks to some simply stunning images by Patrick Zephyr and Raed Ammari. I only remembered these head-on pictures, and forgot what the whole spider looked like.

I had also forgotten, or never knew, that P. insignarius is found here in Colorado. Indeed, it ranges from here east through Nebraska, Iowa, Kansas, eastern Oklahoma, Missouri, southeast Minnesota, Illinois, Indiana, Kentucky, Tennessee, Pennsylvania, southern New England, New Jersey, Virginia, and North Carolina. Look for it in the understory of open woodlands and prairies. The oak thicket with scattered pines in an otherwise grassland habitat where I found this one seems to be the ideal habitat.

P. insignarius is not a terribly large spider. Mature males average just under 5 millimeters in body length, females 5.45 millimeters. The coloration of the female, from all I can gather, is similar to the male, but without the bright white hairs on the carapace, legs, and palps. Both genders have the bushy "eyebrows" that are characteristic of many Phidippus species.

If you are all ready to go searching for jumping spiders now, consider investing in a "beating sheet," or make your own. A friend of my wife who is an accomplished seamstress, whipped one out for me in no time. We chose a heavy, durable canvas (still prone to deformation with a good stiff breeze), about two feet square. Triangular pockets in each corner receive wooden slats arranged in an "x" pattern with a screw in the center to join them.

Beating sheet in use ©knoxnews.com

The beating sheet is held under the branch of a tree or shrub, and a heavy stick or rod is used to sharply strike the branch. All manner of spiders, and insects, of course, can come raining onto the sheet. This is the best way to collect many cryptic arthropods that are seldom seen otherwise.

Sources: Edwards, G.B. 2004. "Revision of the Jumping Spiders of the Genus Phidippus (Araneae: Salticidae)," Occasional Papers of the Florida State Collection of Arthropods. Volume 11. 156 pp.
Hollenbeck, Jeff. 2007. "Species Phidippus insignarius," Bugguide.net

Friday, June 10, 2016

Louse Flies? Are You "Ked"-ing Me?

Until recently, insect diversity here along the Front Range of Colorado this spring has been suppressed by cool, wet weather. How amazing, then, that I should see not one, but two specimens of an insect I had seen only once or twice in all my years. I am speaking of "louse flies" in the family Hippoboscidae.

Back at the end of December in 2009, I volunteered to do a guest blog for my good friend Dave Small after he sent me an e-mail inquiring whether I might know the identity of an insect in an image he attached with his message. I didn’t quite understand the story at first, like why two hunters were involved, and why the insect was adhered to hard candy. The image was clear enough, though, that I could tell what the creature was, and that this was not a tall tale evolved from heavy drinking. Here is the rest of that piece.

Deer and related animals play host to a variety of parasitic invertebrates, including the familiar, slow-moving ticks. Such blood-feeding creatures are quick to abandon a deceased host, however, and so animals harvested during the hunt often yield some strange, living cargo during inspection and dressing.

The specimen discovered by these two hunters is an insect known as a “louse fly,” among the most peculiar of insect parasites. They are much more nimble than ticks, dodging attempts to catch them as they skirt through a host’s fur. Their flattened shape, top to bottom, and talon-like claws enhance their ability to slip between hairs and grip the hide of the host, avoiding licking and biting efforts to dislodge them.

Members of the fly family Hippoboscidae, most known louse flies are actually parasites of birds. The most infamous member of the family, though, is the “sheep ked,” well-known to those who manage flocks of ovine livestock. The adult flies are wingless, but they find each other easily for mating when the host animals crowd together.

Back to the specimen the hunters found, and collected by sticking it with a piece of hard candy. That would probably be a “deer ked,” Lipoptena cervi. Here is a terrific image of a related species, Lipoptena depressa from northern California. Both species have a life history that is typical of the entire family of louse flies, but truly mind-blowing compared to other insects.

Female louse flies do not lay eggs. They grow one offspring at a time, within their bodies, much like mammals. A single larva develops inside the equivalent of a uterus, feeding from a “milk” gland. When mature, it is “born alive,” dropping to the ground where it immediately buries itself and pupates. An adult fly emerges weeks later. Deer ked are winged, at least initially, but females that have found a host will break off their wings, the better to maneuver through the dense, coarse hair of their host.

Wingless deer ked after two days in captivity

While keds are known to transmit certain diseases from host to host, they are for the most part not economically important. Consequently, little is known about them. Kudos to our hunter friends for bringing this one into the spotlight.

The first specimen I found this year landed on my while I was hiking in Aiken Canyon Preserve off of highway 115, about fifteen miles northeast of Penrose, Colorado on Memorial Day (May 30). I recognized it fast enough to grab it while it was tangled up in some of my sparse arm hair.

After chilling the tiny, 3 millimeter creature in the fridge for a few minutes, I dumped it out into a casserole dish to photograph it. Well, it was apparently completely unaffected by the cold and flew off after I fired off only a couple of legible shots. About 30-45 seconds later, from out of nowhere, it landed on my chest. I guess it pays to be a mammal to keep these flies under some degree of control. A couple of days later, I found the fly had self-broken its wings, such that they were mere stubs. Despite that, the insect was still highly mobile and most of my shots were as blurry as when it had flight capability.

The next encounter was at a blacklight set up to attract moths in Cheyenne Mountain State Park on the night of June 4. I routinely scrutinize the most minute of creatures in the event they may be of interest, and much to my surprise there was another "ked." It, too, was fully winged but, perhaps mesmerized by the ultraviolet light, sat motionless and allowed me to take multiple images....most of which are still not optimal because the blame bug is so miniscule.

Want to find your own louse flies? You might volunteer to go hunting game mammals and birds with your friends to get a chance at shaking one loose. Otherwise, good luck. These insects are common, but so seldom stray from hosts that it is sheer serendipity to stumble across one. More than likely, the fly will find you.

Wednesday, June 8, 2016

Strange Behavior Explained (Sort of)

The other day (Monday, June 6 to be exact) I was exploring Adams Open Space behind the public library in Fountain, Colorado with my wife. I happened to notice a small ichneumon wasp on the underside of a leaf and snapped a couple of images. This was the best one, and I was shocked to see a cluster of eggs beneath the wasp's abdomen. What was going on?

It had been my previous understanding that female ichneumon wasps deposited their eggs on or in their host, as they are parasitic on other kinds of insects (and spiders in some cases). Why was this one laying her eggs in a mass on the surface of foliage?

I posted the picture and posed that question to a Facebook group of world authorities on Hymenoptera, the order of insects to which ichneumons belong. The next morning I got an answer, courtesy of one Sasha Varga, a doctoral student in the Ukraine. First, he offered the genus identification of Polyblastus. That was surprise enough because the overwhelming majority of ichneumon wasps can barely be identified to subfamily from images alone. Thank you, Sasha!

Varga went on to explain that "as I understand, egg remains on the ovipositor after unsuccessful oviposition, but only one and why Polyblastus accumulates several eggs I really don't know." I was simply impressed with Sasha's command of the English language at this point. Ok, so now I at least have some clarified information I can run with.

Wait, Jitte Groothuis added a link to an article that might shed a little additional light. Jitte is likewise a PhD student, at Wageningen University in the Netherlands. Wow, this little observation of mine is circling the globe....

The article cited is entitled "Eggs and Egg Loads of Field-collected Ctenoplematinae (Hymenoptera: Ichneumonidae): Evidence for Phylogenetic Constraints and Life-History Trade-Offs." It is authored by Heather M. Cummins, Robert A. Wharton, and Aubrey M. Colvin, all of Texas A & M University. It was published in 2011 in the Annals of the Entomological Society of America, vol. 104, no. 3, pages 465-475. This sounds like it is over my head, too, so let's investigate together.

Apparently, an understanding of this paper hinges on an understanding of the differences in life histories between various groups of ichneumon wasps. Some ichneumons are "idiobionts," which means that further development of the host insect is arrested at the time it is parasitized by the idiobiont. Typically, a pupa stage is targeted, but sometimes a larva host, and the ichneumon wasp larva is invariably an external parasite. Idiobiont ichneumon wasps are also much more likely to be "generalists" with a wider range of host insects they can expolit.

Other ichneumon wasps are "koinobionts," meaning that the host organism continues its development at least until the wasp larva completes its development, at which time the host often (usually?) dies. Koinobionts can be either external or internal parasites, though the wasp larva is usually attached to the host, never straying to another host or otherwise moving freely away from the host. Koinobionts are also much more likely to be specialized on a narrow range of host species, in contrast to the generalist idiobionts.

Our Polyblastus here is a koinobiont. In its larval stage it is an ectoparasite (external parasite) of sawfly larvae. The adult wasp emerges from the cocoon spun by the host sawfly larva. This makes sense. We even found a female Elm Sawfly, Cimbex americana at the same location on the same day, so we know potential hosts are present.

According to the abstract of the article, the egg loads of female koinobionts like our Polyblastus are "significantly larger" than the egg loads of idiobiont ichneumons, though the eggs themselves are smaller in koinobionts. Unfortunately, an abstract is all I could find online. I will amend this post should I secure a copy of the entire paper. Maybe having so many eggs, our female wasp is forced to carry some of them externally? How does she keep from losing some simply in the course of searching for a host? How does she manage to attach her eggs to the host one at a time (assuming she deposits ova singly)?

Once again, an innocent observation turns into a convoluted and puzzling mystery. That is exactly what I love about entomology, though. It is a science that keeps you in a constant state of awe, forces you to think imaginatively, and challenges your research skills to the maximum.

Sources: Carlson, Bob. 2010. "Tribe Tryphonini," Bugguide.net.
Cummins, Heather M., Robert A. Wharton, and Aubrey M. Colvin. 2011. "Eggs and Egg Loads of Field-collected Ctenoplematinae (Hymenoptera: Ichneumonidae): Evidence for Phylogenetic Constraints and Life-History Trade-Offs," Ann. Entomol. Soc. Am. 104(3): 465-475.
Goulet, Henri and John T. Huber, eds. 1993. Hymenoptera of the World: An identification guide to families. Ottawa, Ontario: Agriculture Canada. 668 pp.