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Monday, October 18, 2021

Column: Bug bloodbath

The world of an insect is something out of a Quentin Tarantino film. Dragonfly nymphs gnash their mandibles to devour minnows, and ant colonies wage war. A female praying mantis lops off her mate’s head just as he climaxes. Cue the blood splatters.

“Fish gotta swim and bird gotta fly; insects, it seems, gotta do one horrible thing after another,” writes nature writer Annie Dillard in her book Pilgrim at Tinker Creek.

In the competition for most gruesome, grisly, stomach-turning insect I nominate the parasitoid wasp. These tiny wasps lay their eggs inside living animals. The eggs hatch and the larvae feast on living tissue. Entomologists will tell you that Ridley Scott’s Alien got it right.

When you’re a caterpillar, no one can hear you scream.

The difference between parasites and parasitoids is the damage they do to their hosts. Parasites want to keep a host alive – they don’t want the buffet to close. That’s why people can live for years with hookworms or blood flukes. But parasitoids are killers.

Picture a mommy wasp with a massive stinger. This is a special kind of stinger: it’s called an ovipositor. Mama Wasp can lay hundreds of eggs through her ovipositor, but the spike is also useful for puncturing the silky skin between the exoskeletal plates of a caterpillar.

From far away, the wasp can’t smell her prey, but she does sniff out the scent of plants her host eats. Then she smells caterpillar poop – she’s getting closer.

The innocent caterpillar looks up at the wasp, buzzing above him as he tries to gallop away on his stumpy little legs. She dives down while he bobs and weaves, trying to shake her off. Depending on the wasp species, she may paralyze her catch with venom or just leave him conscious, free to feed on leaves and fatten up.

Then the proud mama zips away.

Wasps will also parasitize aphids, ants, even trees. Insects have pretty basic nervous systems, but surely they can feel the wasp larvae drinking their blood and ripping apart their organs. It’s an image that has haunted naturalists for centuries.

Charles Darwin once wrote, “I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae [one group of parasitoid wasps] with the express intention of their feeding within the living bodies of Caterpillars.”

Parasitism is gory, but it gets a lot weirder. There are parasitoids of parasitoids.

“One startled entomologist, examining a gall [a swollen area on a tree] made by a vegetarian oak gall wasp found parasitism of the fifth order,” writes Dillard. “This means that he found the remains of an oak gall wasp which had a parasitic wasp which had another which had another which had another which had another, if I count it right.”

Give me a minute to uncross my eyes.

Parasitism may sound like a murder on steroids, but there is a bright side. Parasitoid wasps are a good way to control pests in agricultural areas.

In Tulare Country, just down the I-5 from Davis, an insect called the citrus leaf miner attacks orange trees. Leaf miners larvae carve up the leaves of citrus trees and drive orange growers and nursery owners crazy.

Call in the parasitoid wasps.

A species of wasp called Phigalio boharti (named after Richard M. Bohart, an entomologist from UC Davis) does the job well. Researchers at UC Riverside found that the wasps will kill leaf miners on grapefruit, pummelo, orange and lime trees. Parasitoid wasps are also a good alternative to harmful pesticides. In Florida, they’ve actually shipped in wasp species from Australia and Asia to help with the leaf miner problem.

As they say, the enemy of my enemy is my friend.

Just think twice if your friend as a giant ovipositor.

MADELINE McCURRY-SCHMIDT wants to hear your article ideas! Send her an e-mail at science@theaggie.org.

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