Mechanical vs Chemical stimuli - was VFT & Dried flies

Date: Sun Jan 24 1999 - 08:58:07 PST

Date: Sun, 24 Jan 1999 09:58:07 -0700
Message-Id: <aabcdefg213$foo@default>
Subject: Mechanical vs Chemical stimuli - was VFT & Dried flies

In regards to the question about why a VFT would reject a dried fly, Rand
(I think) replied that wetting the fly to get its "juices" up would help,
whereas John suggested that VFTs require movement to get the VFT to
commence digestion.

This brings up the question of whether or not the feeding response of a
VFT is triggered by a mechanical or chemical stimulus. Clearly the
trigger for the trap to close is mechanical (under normal circumstances)
but I have wondered if mechanical stimulus was relevant to trigger the
digestive process.

In my own experience, I have had VFTs reject dry items but not wet ones
(in both cases without mechanical stimulation after the trap has closed)
so my personal suspicion is that the feeding response is a chemical
stimulus. I suspect that most attempts to mechanically stimulate the
trap after closure serve to increase contact of the lobes of the trap to
the prey item, thus producing the necessary chemical trigger. Under
natural circumstances I suspect a struggling insect will likely defecate
while it is being crushed to death and the movement of the insect will
increase surface contact of the lobes of the trap to the necessary
chemical stimulus.

But this all just conjecture on my part. Does anyone know if this has
been studied or have an relevant data?

Rich Ellis, Boulder, CO ""

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