Background/Question/Methods Leaf-tying caterpillars, acting as ecosystem engineers on oak trees, influence arthropod composition on those trees. Both the identity of the caterpillar and that of the host plant are likely to modify these engineering impacts. We examined the effects of host plant species identity and leaf-tier species identity on arthropod communities on eight species of sympatric oaks in eastern Missouri, USA. We predicted that larger caterpillar species would have greater impacts because they build larger ties, and higher quality trees would attract more herbivores, more predators, and produce more frass attracting more scavengers, all resulting in a greater engineering impact. We compared the engineering impacts of one small caterpillar species (Pseudotelphusa sp.) versus one large species (Psilocorsis reflexella) placed into artificial ties on the oak trees. These ties were censused twice during the season for leaftier establishment and arthropod abundance.
Results/Conclusions The identity of the host plant significantly affected the establishment of both species of caterpillars. Pseudotelphusa individuals were more common on black and white oaks than other oaks, while Psilocorsis reflexella individuals occurred more frequently on post oaks. Subsequent establishments of other species of leaf-tying caterpillars were also affected by the identity of the host plant and facilitated by previously occupied ties, irrespective of the identity of the previous occupant. The densities of sucking insects, such as lace bugs, and of detritivores, such as psocids, were both affected by host plant identity. However, the densities of predators, including spiders and lady bug beetles, were not affected by the identity of the host plant, although they appeared to be attracted to established leaf ties. Leaves of these eight species of oaks exhibit varied qualities, possibly attributed to different levels of phenolics. Such disparities in leaf qualities potentially explain their effect on arthropod densities and interactions with the ecosystem engineering impacts of the caterpillars.