#trissolcus

Trissolcus japonicus!!!! (Samurai wasp)

It was the first parasitoid I ever found and what led me down the rabbit hole. I just thought she was the cutest little gal ever…and they introduced me to the concept of classical biological control—importing a natural enemy to combat an invasive species. As this fellas name would suggest, it’s native to Japan (and China and South Korea), but it’s currently established in the U.S. including where I live (Texas.) Let me tell you why that’s a good thing.

T. japonicus parasitizes brown marmorated stink bug eggs, another species from Asia which is highly invasive and devastates crops and forests here. T. japonicus also, like many parasites and parasitoids, has a strong preference for its host! It doesn’t really attack native species that much.

Importing little parasites and parasitoids is actually a highly successful pest control strategy. There are of course a lot of high profile instances of “biological pest control gone wrong”, like that idiot that brought Cane Toads into Australia thinking they would eat locusts. But that guy did NO experiments to see if they even LIKE locusts (they don’t.) And he was using a PREDATOR (which usually doesn’t coevolve with a specific species and eats whatever it can gets its hands on.) So Cane Toads were brought to a place where they have no natural enemies and they bred like crazy eating every native bug in sight. And Australia is a worse place for it.

But when biological pest control is done by researchers who know what they are doing, it’s pretty damn successful. Its been used to combat so many devastating invasives in the U.S. (Cottony Cushion Scale, Spongey Moth, etc…) But the success stories don’t make headlines as often.

At least these Pentatomid eggs are stylish now!

Happy Easter! :)

Spotted at the Rockingham Environment Center, advertising their presumably unpleasant taste, probably derived from the highly aromatic plants they feed on. 

This Pentatomid is native to Australia, but is so overly attracted to the highly invasive and noxious (in both senses of the word) weed Horehound (Marrubium vulgare) that we don’t know what the original host plant was. Given that other known hosts for the bug include Lavender (Lavandula), as here, and Salvia (S. divinorum), it was probably something in the Lamiaceae. 

Horehound is native to many parts of Eurasia and north Africa, but is now found in most parts of the world. It was introduced to Australia as a medicinal plant, supposedly useful against respiratory complaints, but there’s no evidence that it’s actually useful for any such purpose. 

Unfortunately, despite the Horehound Bug’s enthusiastic appetite for Horehound, it doesn’t appear to be very useful as a biological control - and the reason appears to be another species actually introduced as a biocontrol agent, the egg parasitoid wasp Trissolcus basalis. This Platygastrid wasp was originally introduced to Australia in 1933, to control the Green Vegetable Bug Nezara viridula, another Pentatomid species. Not only is the wasp highly territorial, chasing off other parasitoids from whatever area she has claimed as her turf and reducing the number of Nezara eggs that actually get parasitised, it also targets the eggs of at least 25 other species of Pentatomid Bug, including Predatory Shield Bugs that would actually protect crops from other pests. So the wasp’s failures as a biocontrol include making the Horehound Bug fail as a biocontrol.