#1833 - Agonoscelis rutila - Horehound Bug
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.
(That said, the horehound clearwing moth (Chamaesphecia mysiniformis) and the horehound plume moth (Wheeleria spilodactylus) are showing hopeful evidence as biocontrols of the weed.)