When potted cottonwoods were experimentally placed varying distances from box elder trees, we found that cankerworm numbers significantly declined with increasing distance from source box elders, showing that increased distance from box elder resulted in decreased susceptibility to fall cankerworm (Page's [L.sub.a] 309, P [less than] 0.001; Fig.
fremontii) located under box elder (Acer negundo) were colonized by two to three times more cankerworms, and suffered two to three times greater defoliation than cottonwoods growing under mature cottonwoods, or cottonwoods growing in the open.
Key words: Acer negundo; Alsophila pometaria; associational resistance; associational susceptibility, box elder; cottonwood; dietary breadth; fall cankerworm; plant-herbivore interactions; Populus; preference hierarchy; spillover.
Within our study area, early larval feeding is restricted primarily to box elder (Acer negundo).
1989) growing in association with box elder. We compared cankerworm densities and defoliation levels of small trees (0.5-3.0 m in height) located either under a mature box elder, under a mature conspecific, or in the open and relatively isolated from other trees that could serve as sources of cankerworms.
The timing of late instar cankerworm dispersal is heavily dependent on box elder infestation levels, which varied considerably from tree to tree.
One member of each block was placed under box elder, one under a mature cottonwood, and one in the open.
Observationally, we evaluated host preference by estimating fall cankerworm egg densities on box elder and cottonwood.
Scarcity of cottonwood and box elder at this elevation makes previous exposure to these hosts unlikely.
Larvae that had just molted to fourth instar were collected off box elder, and randomly placed in mesh bags (six bags, 10 larvae/bag).
The doe kept up her calling as she passed through a cluster of box elders to my right, and ran out through the gate to join the other deer.
I turned in my stand and, in the dying light, saw a large buck attacking some low-hanging limbs on one of the box elders.
A sinking feeling drained into my belly, but before it had time to settle, the buck inexplicably turned straight toward me, walked about 10 yards, and then curved back toward the box elders. He stopped at what I guessed to be 35 yards, with his vitals perfectly framed between two branches parallel to the ground 20 yards out.