Gall-inducing insects of deciduous and semideciduous forests in Rio Grande do Sul State , Brazil

1. Departamento de Ecologia, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, Porto Alegre, RS, 91501-970, Brazil. (anapgoetz@gmail.com; milton.mendonca@ufrgs.br) 2. Institut Méditerranéen de Biodiversité et d’Ecologie (IMBE), Université d’Avignon et des Pays de Vaucluse, CNRS, IRD, Aix Marseille Université, IUT d’Avignon, Avignon cedex 9, France. 3. CAPES Foundation, Ministry of Education of Brazil, Brasília, DF, 70040-020, Brazil.

Insect-induced galls are anomalous growth on plant organs originating from increases in plant cell number (hyperplasia) and/or size (hypertrophy) (Mani, 1964).Galling insect species can even be separated and identified based on gall morphology along with host plant organ and species (Price et al., 1998).Each galling insect species is responsible for inducing a unique structure, a gall with distinct anatomy and physiology compared to other such species (Shorthouse et al., 2005).Most gallers are species-specific relative to the plant host, with the latter usually belonging to specific plant clades as well, with clear evolutionary associations (Mendonça, 2007).New surveys of these gall-based plant-herbivore trophic networks on unexplored sites and vegetation types can work as repeated tests for these ecological and phylogenetic patterns, with regional preferences either confirmed or revised by new knowledge.
Since the end of the 1980s decade, studies on galling insects increased considerably in Brazil, mainly related to natural history and distribution (Fernandes et al., 2014).Nowadays, work is being carried out in all different regions of this country: North (e.g.Almada & Fernandes, 2011), Northeast (e.g.Nogueira et al., 2016), Central-West (e.g.Araújo et al,. 2015) and Southeast (e.g.Maia & Carvalho-Fernandes, 2016).In Southern Brazil, studies on galling insect diversity are still scarce, however there are recent records for Paraná (Carvalho et al., 2015;Santos & Ribeiro, 2015) and Rio Grande do Sul States (e.g.Dalbem & Mendonça, 2006, Mendonça, 2007, 2011;Mendonça et al.;2010, Toma & Mendonça, 2013).Mendonça et al. (2014) listed insect galls known from the two biomes occurring in Rio Grande do Sul (RS), Atlantic forest and Pampas.Surveys covered different vegetation types, mostly subtropical gallery forests and subtropical moist forests, without being able to represent Seasonal forests, a rather common vegetation type in the region.
This study aims to increase the present knowledge on galling insects and their host plants by surveying Deciduous and Semideciduous Seasonal forests in Rio Grande do Sul State and comparing with already established ecological and evolutionary patterns on gall occurrence.

MATERIAL AND METHODS
This study was carried out in forest fragments of Semideciduous Seasonal (SS) and Deciduous Seasonal (DS) forest formation types, in two localities of Rio Grande do Sul State, Brazil.SS samples took place in Canela municipality, in an area belonging to the State Electric Company (Companhia Estadual de Energia Elétrica, CEEE-RS).Samples in DS occurred in Santa Tereza municipality, in private property areas with authorisation granted for scientific research.
The SS sites face a Cfb climate (Köppen classification) with average temperatures for the hottest month at 22°C and for the coldest month from -3°C and 18°C (Moreno, 1961).This type of forest formation is characteristic of regions with temperature climatic seasonality and has a percentage of deciduous trees between 25 and 50%, evident in the winter (IBGE, 2012).The DS sites are under a Cfa climate with average temperatures for the hottest month above 22°C and for the coldest month from -3°C and 18°C (Moreno, 1961).As with the SS forests, DS occurs in seasonal environments, having however at least 50% of trees losing leaves in the cold season (Espírito-Santo et al., 2006).
All galls were collected and took to the lab, where they were separated in morphotypes according to external morphology in combination with galled organ and host plant species.Galls were photographed, dissected under stereoscopic microscope to obtain immature galling inducers and characterize and describe galls (shape, colour and number of chambers) according to Isaias et al. (2013).
Part of the sampled galls was kept in sealed plastic bags to obtain adult galling insects.These were preserved in 70% ethanol and identified to the lower taxonomic level possible.However, some gall morphotypes were found empty, which made inducer identification impossible, although there is no doubt these galls were insect-induced.Host plant shoots, reproductive when possible, were identified with the help of taxonomic literature and/or botanical specialists.Biological material is deposited in the scientific collection of the Laboratório de Ecologia de Interações, UFRGS.Host plant taxa were organised according to Angiosperm Phylogeny Group IV classification (APG, 2016).

RESULTS
Overall 89 gall morphotypes were found, with most insect inducer species being Diptera, and Cecidomyiidae having 55% of all galling species.Lepidoptera represented only 3.3% of galling species and 38.2% of the morphotypes could not be identified, either coming from empty galls or only found occupied by parasitoids (Hymenoptera and Diptera).Among all gall morphotypes found here, 48 are considered as new records for the host plant species (Tab.I), comparing with pertinent literature -that is, no mention of a gall on a given plant, with the structure and inducer reported here, could be found.

DISCUSSION
The plant families with most galls in the Seasonal forests of Southern Brazil were Asteraceae, Fabaceae and Myrtaceae, all pointed out as the most common host taxa in Brazilian surveys from different regions (e.g.Maia et al., 2014;Araújo et al., 2015;Maia & Carvalho-Fernandes, 2016).Asteraceae as the family with most galled species also agrees with what was previously found for RS State, according to Mendonça (2007).These members of the daisy family were also recorded as those with the higher number of morphotypes in more recent surveys in RS (e.g.Toma & Mendonça, 2013;Mendonça et al., 2014).
Records of galls on Mikania had the highest contribution to morphotype richness in Asteraceae (10 of the 18 morphotypes in this family), with this genus already known (Mendonça et al., 2014) as a super-host (species or genera hosting many types of gall, Veldtman & McGeoch, 2003).Piper aduncum was the species attaining super-host status, followed by M. glomerata, a plant already considered as a super-host (Mendonça et al., 2014).Piperaceae, having this super-host species, ended up as the second most dominant family in this study, which is uncommon for gall surveys in Brazil.Cecidomyiidae as the most common inducer group was an expected result, since they comprise the richest family among galling arthropods (Gagné & Jaschhof, 2017), being also the most common in the Neotropical region (Gagné, 1994, Espírito-Santo & Fernandes, 2007).
Although leaves were the main galled organ, as is usual in other work (e.g.Araújo et al., 2015;Maia & Mascarenhas, 2017), leaves and shoots had similar proportions, as was found by Toma & Mendonça (2013) for a nearby survey in araucaria forest in RS.Mendonça et al. (2014), considering different localities and vegetation types, pointed out that in RS there were even more galls on shoots than on leaves.This pattern of no high prevalence of galls on leaves might be related to forest deciduousness in more temperate vegetation types in Brazil, which by losing leaves during winter could represent a less lasting resource for gallers.This hypothesis, along with the geographic question of similar results on intermediate latitudes [African savanna, Veldtman & McGeoch (2003); Neotropical rupestrian fields, Carneiro et al. (2009)], as suggested by Toma & Mendonça (2013), needs more specific tests and more regional comparisons, however.
Fusiform galls were more frequent, differently from other sites where the globoid form is more common (Maia et al., 2014;Nogueira et al., 2016), the latter being the second most common.Again, this was also found previously for the RS State by Toma & Mendonça (2013) and Mendonça et al. (2014).This pattern might be correlated with the abovementioned relatively higher frequency of shoot galls in these more meridional environments -shoot galls are usually fusiform (Isaias et al., 2013;synonymized with elliptical).
The 48 new gall morphotype records (compared to the available literature, e.g.Almada & Fernandes, 2011;Toma & Mendonça, 2013;Mendonça et al., 2014;Maia et al., 2014;Araújo et al., 2015;Maia & Carvalho-Fernandes, 2016;Nogueira et al., 2016,), show how important survey work still is in this region, increasing our basic knowledge on galling insects.This expressive number of potentially new species of gallers reveals that especially in little explored different forest types (as seasonal Deciduous and Semideciduous forests), there is still much to be gained in terms of new data and new taxa.
Fig. Forest type Fig. Forest type