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.