What’s that Bug on My Rabbitbrush!

Rabbitbrush BeetleIt’s a black grubby thing that, when the light is just so, is metallic green. This is the third year I’ve watched this annoying pest chomp most of the green leaves from the bush. This normally tough shrub is dying a slow death. This year I pruned so much dead wood that the shrub is now half the size it once was.

The bug is Trirhabda nitidicollis, or Rabbitbrush beetle. Rubber rabbitbrush, or Ericameria nauseosa (formerly Chrysothamnus nauseosus), is the host plant for this yellow and black striped beetle. It is the beetle’s larvae that is giving me fits. The adult beetle doesn’t do much damage. Apparently the adult lays its eggs in the soil under a rabbitbrush, where they overwinter. Spring rains lure the larvae out to search for food.

Rabbitbrush

After three years of being munched, my shrub is looking a little haggard.

The grubs usually appear the first part of June in my yard. I was diligent with my controls last year and was expecting a smaller assault. But, alas, the crawly worms are marching up the stems in the usual concentration. So, I’m employing all of my annihilation strategies:

Forceful blast of water from the hose. This is my favorite early morning attack as it’s quick and easy to knock the little buggers off before work. Naturally, I hope the blast will knock them silly so they won’t find their way up the shrub again. Objectively, I’m certain this tactic does little more than delay the assault.

Pick and Pluck: After work, I arm myself with an empty yogurt container. I pick, pluck, flick, and knock them off and into the cup. It takes about an hour to rid the shrub of the crawling masses. It’s tempting to think I’ve won. But I know the shrub will be covered in black spots again in about an hour.

Rabbitbrush and Western wheat grass

Is the Western wheatgrass (Pascopyrum smithii) taller this year or is the shrub smaller?

Last year, I filled the container with soapy water to kill the larvae. But this year, I have a devious plan. This year, you see, my chickens will get a nice little treat. I am really excited to see the hens enjoy the dirty little bugs. I toss the lot of them into the pen with glee. The girls eye the squirming mass suspiciously and flee into the coop. What! They didn’t even try one. I walk away in disgust.

Bring in the birds!: If my fickle birds won’t eat them, maybe the wild population will enjoy the bugs. Birds need bugs to feed their young and lucky for me I’ve noticed a new nest in the backyard. So, I just need to lure the birds to this part of my real estate. I rig up a bird bath next to the rabbitbrush.

But I wonder: Why haven’t the birds found this feast in the two previous years?

I do a little snooping online. Let’s look at the Latin name again: Ericameria nauseosa. I should have been wise to this a lot sooner. “Nauseosa” is a great clue that something about this plant is unpalatable. It turns out that rabbitbrush leaves have terpenoids that cause nausea if ingested. Grazing animals avoid rabbitbrush, except in the winter when the levels of terpenoids are reduced. Somehow the rabbitbrush beetle evolved with the ability to tolerate this chemical.

No doubt the larvae, after consuming so many leaves, also contain high levels of terpenoids that would make a bird or other predator ill. Hence, the wild birds and my hens have no interest in helping me save my shrub. Bugwood Wiki lists only a few predators for the rabbitbrush beetle larvae: several stink bug species and the five-spotted lady bug.

I guess I need to apologize to my chickens for calling them “stupid” and, well, “chicken.”

Anyone got any stink bugs? I’ll trade you for a rabbitbrush beetle!

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