Ants, stem borers, and pubescence in Endospermum in Papua New Guinea

The stems of the ant-plant, Endospermum labios Schodde, serve as colonizati on sites for the ant, Camponotus quadriceps F. Smith. They are also subject to damage by insect borers. We sampled young E. labios trees in disturbed forest to compare evidence of stem boring insect and stem miner damage in p lants with and without colonies of C. quadriceps. Dissections of a subsampl e of plants showed that dipteran stem borers and stem miner damage were sig nificantly more common in plants lacking C. quadriceps colonies than in pla nts with established colonies. Evidence from these dissections and from fie ld counts of meristem damage caused by emerging borers suggested that coleo pteran stem borers were also more abundant when ants were nor present. In addition to the incidence of stem boring insects and ant colonies, we ex amined relative levels of leaf pubescence by measuring trichome density and leaf size for E. labios trees. We found that trichome density was signific antly greater in trees with evidence of prior shoot damage (presumably from stem borer emergence at the meristem) but was not significantly related to the presence or absence of an ant colony. This prompted us to compare tric home density on leaves of nearby small trees and of different branches of t he same tree, pairing a stem/branch that appeared damaged with one that app eared healthy Trichome densities on leaves from damaged stems and branches were significantly greater than were trichome densities on healthy branches and stems. Based on these empirical data, we present several possible expl anations for the patterns of association between ants, stem borers, and pub escence. Although feeding preference rests with a common folivore showed no effect of trichome densities on leaves, we suggest further study on how tr ichomes may affect ovipositing stem borers.