The Effects of Mutualism with Ants on Antianthe Expansa, A Neo-Tropical Treehopper (Membracidae: Homoptera)
Ferguson, Bruce G.
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Interactions between membracids and ants are highly variable. Mutualism may significantly increase membracid survivorship and the magnitude of the increase may depend on the species of attendant ant. This study examines the mutualism between Antianthe expansa and several species of ants at a study site in Monteverde, Costa Rica. Differences among behaviors of attendant ant species were observed and quantified. A census of twenty host plants demonstrated that Pheidole sp. maintain significantly higher ant to membracid ratios than Crematogaster nigropilosa, Myrmelachista zeledoni, or Pheidole biconstricta (t-test, p<0.05). Furthermore, Pheidole were shown to be more aggressive than C. nigropilosa in driving off potential competitors of A. expansa. Pheidole attacked and dismantled adults of Alchisme grossa, a nontended membracid, which were pinned to the host plants, while C. nigropilosa ignored the intruders. A survivorship study was carried out to compare mortality of nymphs on tended plants with mortality of nymphs on plants from which ants had been excluded. T-tests between regression coefficients of survivorship plots showed significantly higher (p<0.0l) survival rates on tended plants, with aggregations tended by Pheidole showing higher survival rates than others. In conclusion, mutualism with ants can significantly increase A. expansa survival rates. Pheidole ants, by virtue of maintaining greater ant to membracid ratios and greater aggression toward competitors and predators of A. expansa, cause a greater increase In survivorship than the other ants found at the study site.