Another Micro Mystery

One way that I find insects in winter is by scraping off paper wasp nests that have been abandoned by the past season’s generation of wasps, and placing the nests in a transparent container. What usually happens is that one or more kinds of insects will eventually emerge from these nests. Allow me to share one example.

Dibrachys sp.

I started collecting recent, abandoned paper wasp nests (Polistes metricus is the common species around our home here in Leavenworth, Kansas, USA) when I saw a social media post by Sloan Tomlinson (@thatwaspguy on Instagram). He had reared a type of small parasitoid wasp as a result: the eulophid wasp Elasmus polistis. That species is a parasitoid of the brood (larvae, pupae) of paper wasps. Cool. I could add another species to my home biodiversity list.

So many tiny wasps!

I was excited to find, in January of 2022, that this method had worked, as I saw tiny wasps running around inside the container with the old paper wasp nest. Photographing the little creatures, and then cropping those images, it became apparent that what I had was not what I expected. I was left with a mystery that took me awhile to solve, even though I’m fairly good at researching.

I eventually found a journal article chronicling a study of various parasitoids of paper wasps collected from nests in Missouri, the state immediately adjacent to Kansas. In fact, Leavenworth is right across the Missouri River from Missouri. One of the creatures listed was a wasp in the family Pteromalidae. They had only eighty-seven specimens, though. I was looking at hundreds by the time they finished emerging.

Male wasps attempting to mate with a female.

The species name given was Dibrachys cavus. More recently, it has been revealed to be a “species complex,” and has a new assigned name: Dibrachys microgastri. It represents one of *three* species, any one of which could potentially be my creature. Collectively, they are parasitoids of pretty much any insect with complete metamorphosis. That makes it difficult to determine exactly which one I have. Even placing a specimen under a microscope might not be enough magnification for these two-millimeter wasps.

Dibrachys is unusual for a single genus of wasps in having such a wide range of potential hosts. At least some species, or perhaps most, are hyperparasitoids of tachinid flies and braconid or ichneumon wasps that are themselves parasitoids of moth pupae. This makes me wonder if these minions are part of this puzzle that I documented in 2022.

I find unsolved mysteries intriguing, and delight in them even if I never reach any verifiable conclusion. There will always be *something* that defies explanation in the natural world.

This little cobweb weaver spider may have been making a killing, literally.

Sources:Gibson, Gary A.P., John T. Huber, and James B. Woolley (eds). 1997. Annotated Keys to the Genera of Nearctic Chalcidoidea (Hymenoptera). Ottawa, Ontario: NRC Research Press. 794 pp.
Peters, R.S. & Baur, H. 2011. A revision of the Dibrachys cavus species complex (Hymenoptera: Chalcidoidea: Pteromalidae). Zootaxa, 2937 (1), 1-30.
Whiteman, Noah K. and Brett H.P. Landwer. 2000. Parasitoids Reared From Polistes (Hymenoptera: Vespidae: Polistinae) Nests in Missouri, With a State Record of Elasmus polistis Burk (Hymenoptera: Elasmidae). J Kansas Ent Soc 73(3): 186-188.

Wasp Wednesday: Perilampid Wasps

Do you remember that old saying that “good things come in small packages?” That is certainly the case with the compact little wasps known as perilampids (family Perilampidae). They range in size from 1.3-5.5 millimeters in length, but oh are they spectacular. Many, if not most, are brilliant metallic green or blue. Some are wholly black in color. They can be easily confused with small cuckoo wasps in the family Chrysididae, and are sometimes found in similar situations, especially around aphid colonies, or the extrafloral nectaries of sunflowers.

My latest encounter with a perilampid was indeed on a sunflower plant, where it was intent on imbibing the sweet excretions from the hairy stem. I recognized it as a perilampid by the short, strongly elbowed antennae, and the abdomen, which in perilampids is shaped more or less like a triangle or an inverted pyramid. Cuckoo wasps have an oval or rounded abdomen without sharp corners.

The beauty of these tiny insects is more than matched by their bizarre lifestyle. They are parasitic in the larval stage, usually on other parasitic insects like the larvae of tachinid flies, or ichneumon wasps or braconid wasps living as parasites inside caterpillars or other insect larvae. This is known as “hyperparasitism,” whereby they are parasites of parasites.

Even stranger is the way the wasps find their hosts. The female perilampid “broadcasts” large numbers of eggs, laying them on leaves, buds, cracks in bark, under lichens, and in other locations where the larvae that hatch might have hope of encountering a host. She may deposit as many as 500 eggs in this manner. A flattened, mobile larva (“planidium” or “planidiform”as scientists call it) hatches from each egg, and attempts to attach itself to any moving object by its mandibles. Obviously, a great many such planidium larvae fail because they glom onto the wrong animal.

Those that are successful in finding the appropriate secondary larval host then penetrate the host’s cuticle. Once inside they begin searching for the primary host, a parasite of the secondary host. They will then enter that larva in the same way. There they wait until this primary host pupates. The perilampid larva then exits, molting into a grub-like larva that feeds as an external parasite. It goes through two or three more instars (the intervals between molts) before pupating itself inside the host cocoon or puparium.

Some perilampids in the subfamily Perilampniae are able to adjust their life cycle in the absence of a primary host, simply feeding as a parasite on the secondary host. Perilampus hyalinus is such an example, able to complete its life cycle as a parasite of certain sawfly larvae (Diprionidae, Tenthredinidae) if no primary host is contained within it. Another species of Perilampus is recorded from immature grasshoppers (Acrididae), gaining access via flesh fly parasites (Sarcophagidae). Still other species in the subfamily are recorded as primary parasites of lacewing larvae (Chrysopidae), wasp larvae (Sphecidae), and beetle larvae (weevils in the Curculionidae).

The life cycles of members of the subfamily Chrysolampinae are less well known, but records indicate beetle larvae (Lycidae, Anobiidae, Nitidulidae) as hosts.

The classification of perilampids has given scientists fits. They are variously set aside as their own family (Perilampidae), or lumped in with the Pteromalidae. Even if ascribed to their own family, those members of the subfamily Chrysolampinae are usually put into the Pteromalidae. I don’t get it either. The number of recognized genera is also up for discussion. Some authorities recognize only fifteen genera in the world, whereas others suggest there may be as many as twice that number (thirty genera). There are 260-277 species currently recognized, with 36 species in North America north of Mexico (in five genera). Many more species await discovery and/or names and descriptions.

Sources: Goulet, Henri and John T. Huber (eds.). 1993. Hymenoptera of the World: An identification guide to families. Ottawa, Ontario: Agriculture Canada. 668 pp.
Pitkin, B.R. 2004. “Perilampidae,” Universal Chalcidoidea Database, Natural History Museum, United Kingdom
Grissell, E. Eric and M. E. Schauff. 2003. “Family Perilampidae,” Systematic Entomology Laboratory, USDA Agrigultural Research Station, Beltsville, Maryland.
Grissell, Eric. 2010. Bees, Wasps, and Ants: The indispensable role of Hymenoptera in gardens. Portland, Oregon: Timber Press. 335 pp.