(Beyond Pesticides, December 1, 2017) Ichneumonid wasps (family Ichneumonidae), are a widely distributed parasitoid wasp family within the order Hymenoptera. The name “ichneumonid” comes from Greek words meaning “tracker” and “footprint.” And females do indeed hunt for suitable “hosts” by first identifying the organism’s food source. Once a suitable host is found, females deposit eggs onto the unsuspecting insect larvae where, within ten days to several weeks, the Ichneumonid larva kills the host by feeding on its body fluids before it emerges. They are also known as “scorpion wasps” for the extreme length and curving motion of their segmented abdomens. Note: both adult males and females are stingless, and feed on nectar.
The discovery of Ichneumonidae was so troubling to many that, in 1860, Charles Darwin wrote a letter to the American naturalist Asa Gray, saying:
“I own that I [should wish to] see as plainly as others do…evidence of design and beneficence on all sides of us…I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars, or that a cat should play with mice.”
The parasitic behavior of Ichneumon wasps was the inspiration behind the “Alien” movies’ “face-hugger” and “chest-burster” alien species.
The Ichneumonidae, arguably the largest animal family, contains about 4,000 species in North America alone. There are an estimated 60,000 to 100,000 ichneumonid species distributed worldwide, more than any other Hymenoptera family including ants and bees. Though considered to be especially species-rich in high latitudes, ichneumonids can be found in North America during spring and summer in a majority of wild habitats including forests and wetlands, as well as urban lawns and green spaces.
Ichneumonids look like slim stinging wasps, having long legs and noticeably longer antennae containing 16 or more segments whereas other wasps have 13 or fewer segments. Both sexes can be found tapping their antennae across logs or tree trunks.
Ichneumonid wasps are some of the larger parasitic wasps. Adult size, form and color varies widely based on the size and food source of its larval host. Consequently, some may be brightly colored, while others are brown or tan. The largest ichneumonids of North America, those of the genus Megarhyssa (or giant ichneumonids) can reach 5 cm in length.
While their wings may be shaded blue or brown, ichneumonid wing structure varies slightly from other wasps – the main distinguishing feature being the added “venation” (or, vein arrangement) on its forewings.
Female ichneumonid wasps have a long “ovipositor,” or egg-laying organ. (In stinging hymenopterans, the stinger is a modified ovipositor.) The female’s ovipositor has a tiny ionized manganese or zinc (metal) tip which allows her to drill through bark to reach wood-boring hosts. Interestingly, such high metal concentrations are also found in the wasp’s hardened mandibles, allowing the newly emerged adult to chew a way out of the wood in which the prey larva was encased.
She uses her long ovipositor to inject eggs into a host’s body. The length of the ovipositor allows the female to inject eggs into leaf-rolling or stem-boring insect larvae remarkably (to a human’s viewpoint) hidden from view. A female will use her antennae to sense vibrations made when grubs or pupa feed.
Males tap their antennae only when in search of mates. They have neither stingers nor ovipositors.
Ecological Role and Threats to Existence
Being effective insect parasitoids, ichneumonid wasps play an essential role in the majority of ecosystems. Acting as biocontrol agents, they have been incorporated into managed biocontrol programs.
When in search of hosts to parasitize, female ichneumonid wasps target a wide variety of larvae or pupae of so-called “pest” insects. Ichneumonid wasps are considered highly beneficial as they are immensely helpful in decimating crop-damaging insects before they reach the adult, reproductive stage. Such hosts include tomato hornworms, boll weevils, forest yellowjackets, wheat stem sawflies, cutworms, birch leafminers, cabbage loopers, as well as both corn and wood borers.
When not in search of hosts, solitary ichneumonid wasps can often be seen feeding on nectar and sap of native flowers, shrubs and trees. Foraging adults prefer members of the carrot family Apiaceae (or Umbelliferae). These plants are usually aromatic and contain an umbrella-shaped “inflorescence.” Multiple broad-faced flowers (acting like a welcome mat, or landing pad), enables ichneumonid wasps to clamber across multiple flowers in a single visit, which effectively pollinates the plants.
Ichneumonid wasps travel up to 625 m. These lengthy journeys allow for wider pollen dispersal. However, some adults have been shown to revisit certain locations within days or weeks.
Like other insects, including those providing biological control and pollination services, ichneumonid wasps can be poisoned by the spraying of insecticides. In addition, the cosmetic application of toxic herbicides along the perimeter of our lawns, or across large swaths of farm fields, can destroy ichneumonid waps favorite plant food source, the Apiaceae. Without a viable food source, ichneumonid numbers dwindle, as adults become weak, inactive, and are more susceptible to disease.
How to protect the species
Learn to recognize insects. Learn how to identify and conserve flowering plant species. (Stop to appreciate their smell, color, and allure.) Protect biodiversity in every way you can using Integrated and Organic Pest Management. Remember: Exterminating pests does not mean similar pests will not return. Use least-toxic pesticides only as a last resort, carefully choosing the product least likely to harm insect predators and parasitoids. To keep pests at bay, start by identifying and eliminating pest entry ways as well as food and water sources. Toxic chemicals used on your lawn, parks, or sports fields, devastate the microbes needed to sustain a well-balanced food web.
To ensure a healthy and biodiverse environment for ichneumonid wasps to mate and feed, work collaboratively with neighbors to enliven microbial activity in your lawns or gardens. Replace a portion of your grass lawn with the native plants adapted to your region. Over-seed and apply “top-dressing” (ex- compost) to your lawn, or garden. Aerate soil to allow water to permeate through and stay where it should.
When wishing to incorporate ichneumonid wasps into an IPM strategy, remember, if the goal is to encourage beneficial ichneumonid wasps to deposit their parasitoid eggs into “pest” insect larvae, you need to offer ichneumonid adults sustained access to nectar plants. As ichneumonid wasps are attracted to aromatic plants in the carrot family, try adding varieties such as fennel, parsley, parsnip, dill, cumin, coriander, or chervil to your garden, or grow these plants in pots.
Further research in natural as well as biological control is always needed! Support the Organic Agricultural Research Act. Find out about quantitative biodiversity surveys in your area and their data on ichneumonid species diversity and habitat-hotspots. Keeping such records today will help future conservationists and entomologists make informed ichneumonid wasp protection decisions.
Remember: Avoid using insecticides indoors (or in your garden) as residues can persist in homes for over a year. Visit Beyond Pesticides’ ManageSafe database to learn about least-toxic alternatives for indoor and outdoor pest problems.
Brisbane Insects and Spiders: www.brisbaneinsects.com
Bug Guide: https://bugguide.net/node/view/150
Washington State University, Tree Fruit Research and Extension Center (Orchard Pest Management Online): http://jenny.tfrec.wsu.edu/opm/displaySpecies.php?pn=920
Missouri Deparment of Conservation: https://nature.mdc.mo.gov/discover-nature/field-guide/ichneumon-wasps
McGill University, Quebec Biodiversity Website: http://redpath-museum.mcgill.ca/Qbp/2.About%20Biodiversity/surveys.htm