Buggy Control Systems

[From Bruce Abbott (950524.1000 EST)]

Rick Marken (950523.2045)

Bruce Abbott (950523.1115 EST) --

The signal to stop flying comes from sensors on the foot pads.

Signalus-response?

Not necessarily, but I don't seem to have a fly/bee wiring diagram here in
front of me at the moment, so it's a little hard to tell. Bees are able to
keep the flight motor running while within the hive in order to provide hive
"air conditioning," so for bees at least, there must be some means to
override the "stop" signal ordinarily produced by footpad pressure. This
would suggest that foot-pad pressure is only one input of a more complex
input function. The inhibitory output signal that stops the flight motor
probably appears when there is an error in any of several control systems.
One might propose that, while in flight, footpad contact with a surface
changes the state of (contact AND motor off) to false (reference set to
true); hive temperature above reference might alter the reference for this
lower-level system to true. On the other hand, footpad input might act as a
"kill switch," but one that can be overridden by the temperature control
system. Another possibility is that the footpad signal is generated only
with a _change_ from no pressure to pressure. With the bee already down,
this footpad transient would not occur. Who knows? I don't have the
necessary information on which to base a sound model, but it may be out
there. Is there a fly/bee expert in the house?

By the way, I'm finding a treasure-trove of control system research in this
area. Did you know about it? Next time you're in an academic library, take
a look at _The Journal of Experimental Biology_. It would appear that
biologists, at least, are having little trouble getting control system
studies published, [Example: Kittmann, Rolf (1991). Gain control in the
femur-tibia feedback system of the stick insect. _Journal of Experimental
Biology_, _157_, 503-522.] Most of these reports do not include a computer
simulation of the system under study; nevertheless they often provide
valuable information about the structure and function of some of the basic
control systems found in insects and other animals. Even at the insect
level these systems are impressively complex and subtle. I would encourage
anyone who is interested in understanding/speculating about control systems
from a basic nuts-and-bolts physiological perspective to take a look at this
literature.

Regards,

Bruce