Parasitic Wasps

It may sound like the title of a cheesy horror movie, but most parasitic wasps are your friends in the garden. That being said, there are some really strange truths about parasitic wasps that I can't wait to share with you!.

Tomato hornworm covered with the cocoons of pupating braconid wasps (David Hill) (CC BY 2.0)

Parasitic wasps are not the hornets or wasps that plague summer picnics. Parasitic wasps tend to be tiny and they prey on garden pests, especially plant-sucking varieties, such as the eugenia psyllid. Also known as parasitoid wasps, this distinct group has evolved to lay their eggs on or in the body of their victim. When the eggs hatch, the larvae use the host’s body for food. Okay, it does sound like a cheesy horror movie! And it’s happening around you all the time. Unfortunately, some of these warrior wasps also attack other beneficial insects. Those wasps are called hyperparasitoids.

Check out this amazing video of a parasitic wasp depositing eggs in an ant!

Cees van Achterberg and José María Durán CC BY 3.0

Like other wasp species, parasitic wasps have segmented antenna, only more. Parasitic wasps have 16 or more segments! There are two major varieties of parasitic wasp: Braconid [brac·o·nid] and Ichneumonid [ik·neu·mon-id]. The only real difference between the two species is their wing vein patterns (venation). Braconid wasps do not have a cell in the middle of the wing, whereas the Ichneumonidae do, but you’ll probably never notice. 

Ichneumonid wasps

Ichneumonid wasps vary greatly in size, ranging from a few millimeters to 7 or more centimeters. They tend to be bright yellow or black. There are 24,000 known species with an estimated total of 60,000-100,000, or more, making them the most varied members of the hymenopteran family. Unlike the Braconid wasp, female Ichneumons deposit venom into hosts, along with their eggs. Only the larger varieties of ichneumons can sting humans. Male wasps do not have stingers.

Braconid wasps

Braconid wasps are usually brown or black and some have red markings. There are 17,000 known species of Braconid and some estimates go as high as 50,000 different varieties! How’s that for a family tree? But the truth about Braconid wasps are stranger than any science fiction story. One hundred million years ago, their ancestors were infected with a virus. The wasps that survived that infection were then able to recreate the virus. On purpose! When braconid wasps deposit their eggs, they also inject the virus, which infects the host’s immune system. This infection makes the host unable to defend itself against the wasp’s offspring. The viruses have evolved within parasitic wasps to the point that they are unlike any other virus on the planet!

Braconid wasps have an amazing sense of smell. They also have the ability to be conditioned to respond to certain smells by being rewarded with food (sugar water). Braconid wasps can be trained, within 5 minutes, to respond to explosives, illegal drugs, or human or plant diseases! How bizarre is that?!!?
​
Parasitic wasp menu

When parasitic wasp eggs hatch, they are hungry. Luckily for us, their favorite foods are the larval forms of many destructive garden pests. Parasitic wasps are one of the most effective regulators of insect populations. It is estimated that 10-20% of a region’s insect population is parasitized by these wasps. Ichneumonid wasps also eat nectar and sap.

Wasp menus include moth and butterfly caterpillars (Lepidoptera), beetles (Coleptera), sawflies, ants, bees and other wasps (Hymenoptera) and aphids. Some varieties also eat spiders.

Spraying broad spectrum pesticides can kill beneficial parasitic wasps, along with pests. It is a better choice to keep plants healthy naturally and to maintain an environment with plenty of biodiversity. This way, you can put nature to work for your garden!