Gall-Colonizing Ants and Their Role as Plant Defenders: From 'Bad Job' to 'Useful Service'.

Giannetti Giannetti,Mori Mori,Spotti Spotti,Grasso Grasso,Castracani Castracani

doi:10.3390/insects10110392

Abstract

Galls are neoformed structures on host plant tissues caused by the attack of insects or other organisms. They support different communities of specialized parasitic insects (the gall inducers), and can also provide refuge to other insects, such as moths, beetles and ants, referred to as secondary occupants. This study focuses on galls induced by the oak gall wasp Andricus quercustozae and secondarily colonized by ants in a mixed oak forest. A field survey and two experiments were carried out to a) study ant (species-specific) preferences for different features of the galls, b) describe differences in gall architecture due to ant activity, c) analyse the effects of the presence of gall-dwelling ants on plant health. The results show that there are differences between ant species in gall colonization and in the alteration of gall opening and inner structure. We verified that gall-dwelling ants protect their host plants efficiently, offering them an indirect defence mechanism against enemies (predators and pathogens). The data suggest a new paradigm in ant–plant relationships mediated by the presence of galls on the plants whose ecological and evolutionary implications are discussed.

Highlights

Galls are neoformed structures on host plant tissues caused by the parasitic action of insects or other organisms [1,2,3,4,5]
Truncata showed more than one type of colony composition, while a complete colony with queen and larvae was recorded for all the other species
The present study is a first survey and analysis of the ant colonization of galls induced by oak gall wasp Andricus quercustozae in Italy showing the importance of ants as plant defenders mediated by these structures

Summary

Introduction

Galls are neoformed structures on host plant tissues caused by the parasitic action of insects or other organisms [1,2,3,4,5]. The global richness of gall-inducer insects is estimated at about 133,000 species [4,8,9]. Gall wasps (Hymenoptera: Cynipidae) constitute a relevant group of gall-inducing organisms, with roughly 1400 described species [6]. They mainly prefer a range of oak species as hosts, but the use of other plants is described (e.g., trees of the Fagaceae family and herbs of the Asteraceae, Lamiaceae, Rosaceae and Papaveraceae families) [6,10]. The highest species diversity is found in the Nearctic region, with an estimated 700 species [7,11]

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