A series of field studies was stimulated by the unexpected finding of a band of junipers (Juniperus virginiana) bearing heavy infestations of bagworms, the band running south-southwest to north-northeast through a woodlot (near Norman, OK) of otherwise lightly infested trees. Fidelity to wind direction was confirmed, and numbers of bagworms ballooning from 3.05 m to 36.58 m was measured, with Tanglefoot® traps mounted on metal fence posts. Ballooning numbers were satisfactorily described with a negative exponential model incorporating both gravitational and trap losses. No significant difference was found between ballooning distances achieved by larvae with and without early-stage bags. A study of infestation levels on ornamental junipers planted around houses on the north and south sides of east-west streets revealed both a strong front- vs. backyard difference, and a weaker but statistically significant side-of-street effect. Patterns reflecting short-range dispersal were found in a linear windbreak planting of northern white cedar (Thuja occidentalis), and in a 12 × 44 = 528-tree lattice of planted junipers (near Urbana, Illinois). A “bonfire” effect showing heaviest infestations in mid-lattice, and reduced infestations on the periphery (especially on the windward edge) was postulated and confirmed. Studies of the effect of increased “target” size of larger trees, and of the incidence of apparent bird and small mammal predation, are also reported.
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Vol. 142 • No. 2