C. Loudon (home
page)*1 & M.A.R. Koehl 2
1 Dept of Entomology, Univ. of Kansas,
Lawrence, KS 66045, USA; 2 Dept. of
Integrative Biology, Univ. of
California, Berkeley CA 94720-3140
Many
organisms increase the air or water flow
adjacent to olfactory surfaces when
exposed to appropriate chemical stimuli;
such "sniffing" samples fluid from a
specific region and can increase the
rate of odorant molecule interception.
We used hot wire anemometry, high-speed
videography and flow visualization to
study air flow near the pectinate
antennae of male silkworm moths (Bombyx
mori). When exposed to conspecific
female sex pheromone, male B. mori flap
their wings through a stroke angle of 90
to 110° at about 40 Hz without flying.
This behavior generates an unsteady flow
of air (mean speed 0.3 to 0. 4 m/s)
towards the antennae from the front of
the male. A pulse of peak air speed
occurs at each wing upstroke. The
Womersley number (characterizing the
damping of pulsatile flow through the
gaps between the sensory hairs on the
antennae) is <1, hence pulses of faster
air (at 40 Hz) should move between
sensory hairs. Calculation of flow
through arrays of cylinders and random
walk simulations suggest that this wing
fanning can increase the rate of
pheromone interception by the sensory
hairs on the antennae by at least an
order of magnitude beyond that in still
air. Although wing fanning produces air
flow relative to the antennae that is
about fifteen times faster than that
generated by walking at top speed (0.023
m/s), air flow through the gaps between
the sensory hairs is about 560 times
faster because a dramatic increase in
the leakiness of the feathery antennae
to air flow occurs at the air velocities
produced by fanning. The pressure drop
across single antennae was measured for
both male and female antennae mounted
over orifices such that air was forced
to pass through the antennae. Resistance
to flow of both male and female antennae
(Pa?s/m) was approximately independent
of air speed and was higher for male
antennae. Drag forces were measured on
both male and female antennae using a
novel terminal velocity assay. By
combining the measured resistance and
the drag forces, the proportion of
approaching air that passes through the
antenna was estimated as about 15% for
both male and female antennae. This
approximate "bluff body" behavior is
likely to be exhibited by pectinate
antennae from a variety of insect taxa
in ambient air speeds of 1 m/s or less.
Index terms:
biomechanics, diffusion, chemosensory,
Bombyx mori.
*For more
information on this topic and to listen
to a radio interview by "Quirks and
Quarks", please see C. Loudon's
home page (http://www.ukans.edu/~entomol/faculty/loudon.html).
Copyright:
The copyrights of this original work
belong to the author(s) (see
right-most box in title table). This
abstract appeared in Session 4–
CHEMICAL AND PHYSIOLOGICAL ECOLOGY
Symposium and Poster Session,
ABSTRACT BOOK II – XXI-International
Congress of Entomology, Brazil,
August 20-26, 2000.