Dispersal of first instar larvae of the felted beech scale, Cryptococcus fagisuga.
Abstract
Dispersal of Cryptococcus fagisuga Ldgr. in a beech forest in southern England was studied using suction traps and sticky traps. First instar larvae and eggs of C. fagisuga had mean terminal falling velocities of about 27 cm/s and 40 cm/s respectively. The larvae were the main dispersive stage and were carried passively downwind from infested trees. In mean windspeeds of <1 m/s larvae dispersed a mean distance of about 10 m from a source tree which was infested from near ground level to the lower canopy. The distance dispersed was proportional to height of take-off and windspeed. In suction traps sited from 1 m above the ground to 6 m above the canopy (18 m above the ground) most larvae were trapped at 1 and 3.2 m above the ground; about 0.7% were trapped at or above the top of the canopy. The larvae dispersed along a short-range steep gradient under the canopy and a potentially long-range shallow gradient above the canopy.