Lps. Kuenen et Rt. Carde, STRATEGIES FOR RECONTACTING A LOST PHEROMONE PLUME - CASTING AND UPWIND FLIGHT IN THE MALE GYPSY-MOTH, Physiological entomology, 19(1), 1994, pp. 15-29
Gypsy moth (Lymantria dispar L., Lepidoptera: Lymantriidae) males flyi
ng upwind to high concentration pheromone sources had lower ground spe
eds, shorter crosswind reversal distances and higher turn rates than m
ales flying upwind to low pheromone doses. Casting flight, crosswind f
light with no net upwind movement after loss of pheromone contact, dev
eloped gradually and was similar in fashion for males initially flying
to the three pheromone doses tested; after plume loss, males' flight
in the upwind direction decreased from 6 cm turn(-1) to nearly 0 cm tu
rn(-1) by their fifth turn (crosswind reversal). After plume loss, upw
ind displacement decreased, crosswind distances and inter-turn duratio
n increased. Ground speeds tended to increase after plume loss, but ai
rspeeds decreased following loss of 10 and 100 ng plumes and remained
constant after loss of 1 ng plumes. Latency to casting was c. 1s as me
asured by cessation of upwind progress and by timing the first reversa
l leg that was down or crosswind after plume loss. Though these measur
es of casting were independent of pheromone concentration, they are me
ans that mask the fact that about 40% of males, rather than cast cross
wind after loss of the plume, continued to move upwind, with wider and
temporally less regular crosswind reversals. Such continued movement
upwind is in sharp contrast to previous descriptions of casting flight
after loss of odour-plume contact. In addition, some males engaged in
'regressive' casting, moving downwind after bouts of 'typical' castin
g. The value of casting and of the continued upwind flight after plume
loss, both possible strategies for recontacting a pheromone plume, ar
e discussed.