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Euschistus on poison hemlock

Was out in the field today and spotted a huge number of Euschistus spp. (most likely servus) congregated on what was later identified as being poison hemlock (Conium maculatum).

There were 8-10 adults on almost every one of these plants which were typically about 2 feet tall. Was along a fence on the outskirts of an alfalfa field. Has anyone experienced this before? We collected some of the bugs and plant to see if they'd lay eggs on it, but it just struck me as odd. Any thoughts?

Strange though...
From going through keys and looking up info on E. conspersus, the specimens we collected don't seem to be that- More likely E. servus. E. conspersus apparently isn't supposed to occur East of the Rockies or have spines like these individuals do...

 
It doesn't have to be
A reference to one species feeding on hemlock doesn't exclude other species doing the same. It really depends on how complete the hostplant records are- and often they aren't very.

 
ah
That makes sense... Pretty sure this group was E. servus.

Articles - insects and hemlock
These articles are in the bibliography of a Nature Conservancy abstract on poison hemlock (the abstract is online here). I haven't read them myself but found some quotes.

Goeden, R. D. and D. W. Ricker. 1982. Poison hemlock, Conium Maculatum, in southern California - an alien weed attacked by few insects. Annals of Entomological Society of America 75: 173-176

Quotes:

"Substantial, but unquantified seed destruction by Hyadaphis foeniculi was noted at several locations, but otherwise poison hemlock suffered little insect injury."

"The larval 'anise swallowtail' usually feeds on Umbelliferae. This butterfly may be in the process of adopting poison hemlock as an additional food plant in California."


This article mentions the aphid Rhopalosiphum conii as a disease vector for hemlock:

Freitag, J. H. and H. P. Severin. 1945. Poison-hemlock-ringspot virus and its transmission by aphids to celery. Hilgardia 16(8):389-410.

Phytochemicals
Most plant poisons can be rendered harmless with the right metabolic adaptations, so even the most deadly plants are eaten by something. If the organisms manage to incorporate the poisons into their tissues, it also protects them against predators.

The catch is that that such adaptations come at some cost to the organism and don't usually work on other kinds of poisons, so the organisms maximize the benefits by specializing on the plant they've adapted to.

If that's the case here, we would expect to find them only on their preferred host, but in good numbers.

***update***
Here's a reference to a Euschistus species that feeds on Conium maculatum

 
Thanks a lot Chuck!
For some reason it looks like we don't have Euschistus conspersus in the guide... Think I should snap a few pics on Monday back at the lab and see about getting that page added?

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