Hiding from defenders: Localized chemical modification on the leaves of an Amazonian ant-plant induced by a gall-making insect (Diptera: Cecidomyiidae)

Abstract

Defense against herbivores is considered the main factor influencing the evolution of specialized ant-plant associations. Early studies have demon strated that ants chemically recognize and recruit on host plant leaves due to herbivory simulation. Gall-forming insects are herbivores that are able to manipulate chemical plant properties and thus could change ant responses. The goal of this study was to evaluate recruitment responses of Allomerus octoarticulatus, an ant species associated with the myrmecophyte Hirtella myrmecophila, which is attacked by a gall-forming insect (Cecidomyiidae). We conducted two different experiments to assess whether, octoarticulatus is able to recognize chemical compounds from galled tissues and whether galled and ungalled healthy leaves represent different chemical stimuli to worker ants. We did not observe differences on recruitment between galled and ungalled leaves. However, gall tissue extracts did not induce ant recruitment on H. myrmecophila, while galled leaves extracts resulted in a stimulus to ant recruitment. These results indicate that insect gall tissues on this myrmecophyte probably do not possess compounds which can be detected by the ants. A local change seems to be very helpful to gall-forming insects because they are protected from, and by, ants which deter herbivores.