Document: JOH-3-43-3

Ecosystem engineering by leaftying caterpillars

LILL, J.T.* and R.J.MARQUIS

University of Missouri-St. Louis, MO ¹

Abstract:
In addition to their trophic and competitive effects, shelter-building caterpillars can act as physical ecosystem engineers on their host plants by creating habitats that are subsequently colonized by an array of other organisms. We hypothesize that these engineering effects will influence the diversity and abundance of future arthropod colonists, as well as the amount of leaf damage experienced by their host plant. In Missouri, approximately fifteen species of leaftying caterpillars are found on white oak (Quercus alba). One species in the genus Pseudotelphusa may act as a "keystone" engineer, in that it creates the first wave of leafties in the early summer that are then preferentially colonized by the remaining species. In order to examine the engineering effect of Pseudotelphusa, we conducted a field experiment in the summer of 1999 in which we manipulated the density of leafties on individual white oak saplings and observed the effects on (1) the abundance and composition of the arthropod community, and (2) the amount of leaf damage accrued throughout the season. In order to separate the caterpillar's engineering effects from its trophic/competitive effects, we created artificial leafties both with and without caterpillars initially present. Compared to controls, the treatments in which we clipped 10% of the leaves into leafties had twice the number of total arthropods one month post-treatment. This pattern was largely due to recruitment of other leaftying caterpillars to trees containing artificial ties. Furthermore, recruitment by leaftying caterpillars to artificial ties initially containing a single Pseudotelphusa larva was double that of initially empty ties, indicating a strong biotic effect (i.e., a colonization cue, such as damage, frass or feeding-related volatiles). This increased recruitment in the + caterpillar treatment resulted in a significant increase in foliar herbivory. Other arthropod guilds (predators, sucking insects) showed no response to the treatments or had a delayed response that was only detected later in the season.

Keywords: herbivory, ecosystem engineer, white oak, caterpillar

This abstract is being presented at: 11:15 AM in session:
Oral Session #26: Invertebrate Herbivore - Plant Interactions.