PARENT SESSION
Oral Session 67: Mutualism - Parasitism III: Ants.
Presiding: K Mooney
Wednesday, August 4, 8:00 AM to 11:30 AM, Meeting Room D 135.

Myrmecophily on Baccharis halimifolia - the effects of an ant-homopteran mutualism on a community of insects.

Altfeld, Laura¹, Stiling, Peter¹, ¹ University of South Florida, Tampa, FL, USA

ABSTRACT- We investigated the nature of interactions among common insects on Baccharis halimifolia in a coastal Florida community. Honeydew-producing homopterans are ant attended on the host plant, B. halimifolia, within this community. It was hypothesized that the density of foraging ants would affect not only the ant-attended homopterans and their predators, as expected, but would have the potential to affect densities of other insects not directly involved in the mutualism, such as leaf miners and stem gallers. Three levels of ant densities (high, ambient and absent) served as treatments in this field experiment. The densities of ants, aphids, mealybugs, coccinellid larvae and adults, syrphid larvae, stem galls, leaf mines and ant damaged mines were measured monthly from May to September 2003. Multivariate and univariate analyses of variance were used to evaluate community and species effects of treatments respectively. MANOVA results were significant for treatment differences in the community of insects as defined above (=.359, df=8, P=0.011). Homopterans and their predators were most abundant on host plants with high ant density (Bonferroni P=0.054 homopterans and P=0.033 predators). Interestingly, leaf mine density and ant-damaged mine density were also highest on host plants with high ant density (Bonferroni, P=0.023 and P=0.003 respectively). Gall density was not significantly affected. Results support the hypothesis that foraging ants affect insects involved in the ant-homopteran mutualism but not in the expected manner. Homopterans persisted on host plants with the highest ant densities. Homopteran predators were most abundant on host plants with highest prey densities, despite high ant densities. Results also indicate that ants may affect leaf miner success on host plants that maintain an active ant-homopteran mutualism.

Key words: plant-insect interactions, myrmecophily