Subject: Re: monarch & mimics - coloration "hypoth"

From: William Calvert <[email-masked]>
Date: Wed, 3 May 1995 22:24:02 -0500

On Fri, 28 Apr 1995, Samuel Sun wrote:

> James Kruse <[email-masked]> wrote:
> >   I have read that monarch munching can cause cardiac arrest in
> > birds.  Ms Fortune noted that birds have been eating monarchs in
> > Mexico.
> >  Does the chemical loose toxicity with time? or are the birds
> > building up some resistance??
> >  Just curious......
>
> My understanding is that different species of milkweeds have different
> levels of toxicity, and since it is the milkweed's toxin that the monarch
> adapts for its use, the toxicity of the adult is largely determined by the
> larval foodplant.  I don't know which species of milkweeds have been
> determined to be the most toxic, but I recall a study that discussed this.
>
> Sam Sun
>
Milkweeds do have different toxicities and toxicities vary within the
species.As a general rule California milkweeds are more toxic than
eastern (east of the Rocky Mountains) and southern milkweeds are more
toxic than northern. This means that fall monarchs that have fed on
Asclepias syriaca are not very toxic. These are the ones that travel to
Mexico.The ones that arrive in the north in June or July have fed on
southern milkweeds and are more toxic. Alfonso Alonso at the University
of Florida is working on the loss of toxicity during the overwintering
period in Mexico. My understanding is that he can show that there is a
lost of toxicity with time. I don't know that cardiac arrest has been
observed in birds after consuming monarchs. They probably vomit first. There
are two main predators of overwintering
monarchs. One, the black-backed oriole, appears to avoid the toxins by
unzipping the butterfly and scooping out the contents, thus avoiding the
exoskeleton where the toxins are thought to be concentrated. The other,
the black-headed grosbeak, appears to be immune to the toxins, but may
have to leave the monarch colonies periodically to feed on other
(presumably less toxic) prey items.

Bill Calvert
Texas Monarch Watch

---

From: [email-masked] (Debbie Hahn)
Date: Tue, 09 May 1995 18:34:00 -0500

W>Message-ID: <[email-masked]>
 >Path: netcomsv!uu4news.netcom.com!netcomsv!uu3news.netcom.com!ix.netcom.com
 >noc.netcom.net!news.sprintlink.net!howland.reston.ans.net!paladin.american.ed
 >auvm!BGA.COM!wcalvert
 >Comments: Gated by [email-masked]
 >Newsgroups: sci.bio.entomology.lepidoptera
 >MIME-Version: 1.0
 >Content-Type: TEXT/PLAIN; charset=US-ASCII
 >Message-ID: <[email-masked]>
 >Date: Wed, 3 May 1995 22:24:02 -0500
 >Sender: "Lepidoptera List (LEPS-L)" <[email-masked]>
 >From: William Calvert <[email-masked]>
 >Subject: Re: monarch & mimics - coloration "hypoth"
 >In-Reply-To: <[email-masked]>
 >Lines: 38

W>On Fri, 28 Apr 1995, Samuel Sun wrote:

 >(presumably less toxic) prey items.

W>Bill Calvert
 >Texas Monarch Watch

I understand that viceroy butterflies, which look similar to monarchs,
are poisonous.

 * QMPro 1.53 * May I leave now?  My brain is full.