GONZALEZ Ana maria
Sugary secretions of wasp galls: a want-to-be extrafloral nectar?
ADRIANA A. RICKERT; CAROLINA ROTHEN; PATRICIA DIEZ; A. M. GONZALEZ; BRIGITTE MARAZZI
ANNALS OF BOTANY
OXFORD UNIV PRESS
Lugar: Oxford; Año: 2017 vol. 120 p. 765 - 774
Background and Aims The most widespread form of protective mutualisms isrepresented by plants bearing extrafloral nectaries (EFNs) that attract ants for indirect defence. Another, but less common, form of sugary secretion for indirect defence occurs in galls induced by cynipid wasps. Until now, such galls have been reported only for cynipid wasps that infest oak trees in the northern Hemisphere. Here, we provide the first evidence of galls that exude sugary secretions in the southern Hemisphere, and ask whether they can be considered as analogues of plants? EFNs. Methods We investigated the ecology and anatomy of galls and the chemical composition of the secretion in natural populations of the host tree. To examine whether ants protect the galls from natural enemies, we conducted ant exclusion field experiments.Key Results The galls produce large amounts of sucrose-rich, nectar-like secretions. No typical nectary and subnectary parenchymatic tissues or secretory trichomes can be observed, instead there is a dense vascularization with phloem elements reaching the gall periphery. At least six species of ants, but also vespid wasps, Diptera and Coleoptera consumed the gall secretions. The ant exclusion experiment showed that when ants tended galls, no differences were found in the rate of successful emergence of gall wasps nor in the rate of parasitism and inquilines infestation compared to ant excluded galls.Conclusions The gall sugary secretion is not functionally equivalent to EF nectar but to arthropod?s honeydew, because it does not provide indirect defence to the plant but rather to the gall-inducing wasp. The gall secretion is analogous to EF nectar only because it represents a food resource for ants, but should not to be considered as nectar in the strict sense of the term, because no nectar-producing structure could be associated to this secretion.