Byers, J.A. 1996. Temporal clumping of bark beetle arrival
at pheromone traps: Modeling anemotaxis in chaotic
plumes. J. Chem. Ecol. 22:2143-2165.
Abstract--
The sequence of arrival of the bark beetles Ips typographus and
Pityogenes chalcographus (Coleoptera: Scolytidae) at traps baited with their
synthetic pheromones was monitored with a portable fraction collector.
Histograms of the natural arrival patterns of both species were nonrandom and
clumped at shorter time scales (1, 2, 4, 5 or 6 minute cells) but appeared
random at larger time scales (10, 20 or 30 min). Monte Carlo generation of
similar histograms showed them to be random at all of these time scales. A
stochastic computer model could graphically simulate insect orientation to
odor sources based on present theories of odor-modulated anemotaxis and
casting. Although this model was used throughout since it assumes only that
insects cast perpendicular to the current wind direction, a second model could
slightly improve orientation success. However, the second model requires that
the insect remember its ground path (upwind) prior to losing the plume (after
an abrupt wind direction change). The effects of casting and flight parameters
on orientation success and randomness of arrival sequence within various
plumes were determined by simulation. Similarly, the effects of random walks
in plume direction, plume width, and wind speed were explored. The results
showed that dynamic random variations in plume direction and especially wind
speed could cause an otherwise random arrival sequence (e.g., under constant
wind) to become clumped and nonrandom. Therefore, the clumped arrival patterns
of bark beetles and other insects, including Spodoptera litura (data from
Nakamura and Kawasaki, 1984), at pheromone sources could result from random-
walk fluctuations in wind speed and wind direction.
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Chemical Ecology