Thin your beets and you'll sometimes find a very small wasp resting on the underside of a leaf. At under 3 mm long, it's easy to mistake for a gnat and wave away. But a great many wasps this size aren't the ones chewing your leaves — they're the ones laying eggs inside the larvae that do. They're working on your side of the garden.
Named in a Sugar Beet Field
This past July, an international research team surveying sugar beet fields in Yining City and Qapqal Xibe Autonomous County, in China's Xinjiang region, gave a scientific name to a wasp that had never had one: Chlorocytus papahemii. The name comes from Hemingway's nickname, "Papa," and the team timed the announcement to July 21, Hemingway's birthday. It's a small wasp with a metallic sheen to its body.
The team had come to those fields for a different reason. Sugar beet growers in the region deal with repeated damage from a weevil, Lixus subtilis, whose larvae bore into the stems. It has been a problem for sugar beet farming across Central and Eastern Europe, the Caucasus, western Asia, and China for a long time. Rather than spray the weevil into submission, the researchers wanted to find a natural enemy that would keep its numbers down.
They found one. Eurytoma curculionum, a parasitoid wasp that lays its eggs in weevil larvae, was confirmed in China for the first time during this survey.
The One That Hunts the Hunter
The newly named papahemii, though, doesn't touch the weevil at all. It lays its eggs in the parasitoid wasp that does. The weevil eats the sugar beet, the parasitoid takes the weevil, and this wasp takes the parasitoid — a chain of who-eats-whom running four links deep.
For a field trying to cut pest damage by building up natural enemies, that isn't welcome news. When these hyperparasitoids — wasps that parasitize other parasitoids — are abundant, the beneficial wasp population you worked so hard to build drops right back down. That's why the team didn't stop at recording one new species and instead mapped out the whole web of relationships. Before you put a natural enemy to work, you have to know what preys on that enemy too, or your predictions won't hold.
Keeping Parasitoid Wasps Around Your Garden
The beets and chard in a home garden are varieties bred from the same species as sugar beet, and spinach belongs to a closely related group. The sugar beet weevil rarely makes it to a backyard plot, but leafminer larvae tunneling through your leaves and aphids draw the same kind of natural enemies. You've probably seen an aphid swollen and hardened into a stiff brown shell. That's where a parasitoid wasp laid an egg — gardeners call it an aphid mummy — and other wasps come after those mummies in turn.
Here's what to look for in the garden today.
- Leave the swollen, hardened aphids right where they are — don't pick them off. In a few days a parasitoid wasp will emerge from inside.
- Don't spray the whole bed just because you spotted a few aphids. The parasitoid wasps will vanish before the aphids do. Better to pinch off the worst-covered leaves or rinse the aphids away with water.
- Plant something with small, densely clustered flowers along the edges of your beds — dill, cilantro, fennel. Adult parasitoid wasps live on flower nectar and save the insects for their eggs.
Next time you're thinning beets, flip a leaf over. If you see a hardened aphid or a very small wasp, leave that spot alone. The less a garden gets sprayed, the longer its parasitoid wasps stay.
