A synopsis of fern galls in Brazil

Galls are neo-formed plant structures induced by species-specific interaction between an inducing organism and a host plant. Lycophytes and ferns are two distinct plant lineages historically lumped together as pteridophytes. A number of authors suggest low gall frequency in lycophytes and ferns, compared to angiosperms. This study aimed at compiling an updated overview of fern galls in Brazil, providing information on hosts, gall-inducing organisms and associated fauna. The synopsis was compiled using existent data and by updating scientific names and gathering new information obtained by the authors in fieldwork. To date, galls have been recorded on 16 fern species but none on lycophytes. However, the inducer was identified at species level in only three gall morphotypes from three fern species, with a doubtful inducer for Pteridium sp. Galls are induced by mites (Eriophyidae) and insects of the orders Diptera, Lepidoptera, Thysanoptera, and Hemiptera, Cecidomyiidae (Diptera) being the most frequent galler insect.


Introduction
Lycophytes and ferns are two distinct plant lineages historically lumped together under various terms, such as "pteridophytes" or "ferns and allied plants" (Smith et al. 2006, PPG I 2016).Interactions between lycophytes, ferns and arthropods, especially in the Neotropical region, are poorly documented, little known and even neglected.
Galls, characteristic neo-formed plant structures created by hyperplasia and cellular hypertrophy that can occur in different plant organs, are generated by species-specific interactions between an inducing organism and a host plant (Mani, 1964;Isaias et al. 2013).While some authors claim that galls can be induced by bacteria, fungi, nematodes, mites and insects (Mani, 1964), others state that their induction is restricted to nematodes, insects and mites (Raman, 2007).Inducers establish a parasitic relationship and manipulate the metabolism of the host plant (Mani 1964, Raman, 2007).
A number of authors suggest low gall frequency in lycophytes and ferns, compared with angiosperms (Mehltreter et al. 2010).The chapter entitled Zoocecidium, published in 1938 in the Manual of Pteridology, is an important review of lycophyte and fern galls (Docters van Leeuwen 1938).Recently, for the Neotropical region, Hanson & Gómez-Laurito (2005) recorded 18 species of ferns with galls in Costa Rica.
The aim of this study was to perform an updated overview of fern galls in Brazil, providing information on host species, gall-inducing insects and associated fauna.

Material and Methods
The synopsis was compiled using existing data, and by updating scientific names and gathering new information obtained by the authors in fieldwork.
Data concerning lycophyte and fern galls were collected from historic reference studies (Houard 1933), in the catalogue of Cecidomyiidae of the world (Gagné & Jaschhof 2017); in 55 articles from inventories of insect galls in Brazil published between 1988 and 2017 and studies carried out exclusively with fern galls (Kraus et al. 1993, Martins & Pimenta 1988, Brown et al. 2004, Maia & Santos, 2011, 2015, Farias et al. 2018).
Lycophyte and fern nomenclatures were updated using the Flora do Brasil 2020 database and the PPG I classification system (2016).
Complementary data were obtained in fieldwork aimed at collecting fern galls in the Atlantic Forest in the following locations: Itatiaia National Park, Serra dos Órgãos National Park, Maricá Environmental Protection Area, Serra do Barbosão Municipal Nature Park (all in Rio de Janeiro state), Campos do Jordão (São Paulo state) and Tiradentes (Minas Gerais state).A total of 12 collections were carried out between 2011 and 2017.All the gall morphotypes were photographed, collected and taken to the laboratory where part of the sample was dissected, in order to obtain immature gall-inducing insects and determine the inducer taxon.Another part was packed in covered plastic pots, labeled and inspected daily until gall rot occurred, to obtain adult gall-inducing insects.Gall shapes were standardized in accordance with Isaias et al. (2013).All the biological material was deposited in the entomological collection of the National Museum (MNRJ) of the Federal University of Rio de Janeiro (UFRJ) and Herbarium of the Teacher Training Faculty (FFP) of Rio de Janeiro State University (UERJ).

Results and Discussion
The first records of fern galls in Brazil were made by Houard (1933).This author reported six gall morphotypes in five fern species (Table 1).In none of these the inducer was identified at a specific level, one gall was mite-induced (Eriophyidae) and five by the orders Diptera, Hemiptera and Thysanoptera.In Niphidium crassifolium, Houard (1933) found that the inducer is a Coccidae (Hemiptera); Maia & Mascarenhas (2017) also recorded globoid gall morphotype on the adaxial side of the leaves of this fern (Figues. 1 E-F).However, other insects, including inquilines (Psocoptera, Sciaridae: Diptera and Corythaica cyathicollis (Costa, 1864) Tingidae: Hemiptera), parasitoids (Platygastridae: Hymenoptera) and an unidentified Diptera larva (likely the galler) were found in recent field studies, which raises doubts about the true identity of the inducer.Some species of Platygastridae (Hymenoptera) parasitize Cecidomyiidae gallers (Johnson et al. 2013).Our group is conducting more detailed analyses in an attempt to clarify this issue.
More recently, Maia & Santos (2011, 2015) recorded two stem gall morphotypes in Microgramma vacciniifolia, one ellipsoid-shaped (fusiform) induced by the microlepidoptera Tortrimosaica polypodivora (Figure 1A), and the other spherical (globoid) and induced by the Cecidomyiidae: Diptera Primadiplosis microgrammae (Figure 1B).Two species of parasitoid wasps (Hymenoptera) were also observed: Torymidae and Tetrastichinae (Eulophidae).In microlepidoptera-induced galls a parasitoid wasp Cheloninae (Braconidae) was also recorded, in addition to an inquiline species of Dasineura sp.(Cecidomyiidae: Diptera).In recent fieldwork, a new gall morphotype was recorded for species of Microgramma squamulosa and M. vacciniifolia.It is a conical and lenticular leaf gall respectively, with a white waxy layer at the opening on the abaxial side of the leaf, whose inducer remains undetermined ( Figures I-J).Maia et al. (2008) recorded a leaf gall on Cyathea sp., without identifying its inducer.In field studies conducted in Itatiaia National Park, a globoid leaf gall not yet identified, induced by Cecidomyiidae (Diptera), was found on Cyathea dichromatolepis (Figure 1C).A lenticular leaf gall induced by a new species of Cecidomyiidae was recorded on Cyathea phalerata in the Atlantic Forest of Pernambuco state, Brazil (Farias et al. 2018).
Leaf galls were recorded on Pleopeltis hirsutissima (Figure 1D), Pleopeltis minima, Serpocaulon catharinae and Campyloneurum nitidum (Figures 1G-H).In the first two species, the morphotype is globoid and induced by Cecidomyiidae (Diptera).In the third fern species the gall is conical and in the last lenticular, both with a white waxy layer at the opening on the abaxial side of the leaf.However, we were unable to identify the inducers.Witches' broom galls on leaves of Dicranopteris flexuosa was registered, probably induced by mites.
The leaves are the most frequently attacked organ and the shape of the gall is predominantly globoid.The galls are induced by mites (Eriophyidae) and insects of the orders Diptera, Lepidoptera, Thysanoptera and Hemiptera, Cecidomyiidae (Diptera) being the most frequent gall-inducing insect.In other parts of the world, there are records of fern galls induced by Hymenoptera (Balick et al. 1978, Houard 1908, 1933, Docters van Leeuwen, 1938, Bera et al. 2003) and Coleoptera (Docters van Leeuwen 1938, Bera et al. 2003).
There are no specific inventories for the lycophyte and fern galls of different ecosystems worldwide.The most important data are from Costa Rica, where galls were recorded on only 18 of the 1,120 fern species cataloged, that is a ratio of 0.016 (no. of ferns with galls/no. of ferns species) (Hanson & Gómez-Laurito 2005).In Brazil, galls have been recorded on 16 of the 1,144 fern species cataloged (Flora do Brasil 2020), a ratio of 0.013.However, the inducer was identified at species level in only three gall morphotypes from three fern species (Maia & Santos 2011, 2015).To date, no lycophyte species have been recorded as hosting galls in Brazil and Costa Rica.However, there are records of five Selaginellaceae species from India, New Guinea, Germany and the Malay Peninsula (Alston 1945, Docters van Leeuwen 1938, Mani 1964, Patra et al. 2009).The estimated number of ferns worldwide is 10,578 species (PPG I).In line with the methodology used by Espírito-Santo & Fernandes (2007) and the data collected to date from Brazil and Costa Rica, we estimate an average of 153 fern species with galls worldwide.According to Espírito-Santo & Fernandes (2007), the Neotropical region is the least studied for galls, despite its substantial plant richness.As such, these values are likely underestimated.
Espírito -Santo & Fernandes (2007) suggest that for angiosperms there is a positive correlation between gall-inducing insects and plant richness.These authors also underscore the presence of "superhost plants", which may confirm a high richness of gall-inducing insects.In Brazil, the greatest gall richness was recorded for the genus Cyathea, with three species and the family Polypodiaceae, with 10 morphotypes in eight fern species.Three gall morphotypes were recorded in Microgramma vacciniifolia (Table 1).
The present synopsis systematized and broadened the records of fern galls in Brazil, thereby contributing to the knowledge of these interactions worldwide.The biological difficulties in obtaining adult insects precluded identifying their specific level or order.In some cases, the identitity of the galler remains unknown.However, the information presented here is important in designing future studies on the interactions between ferns and insects, especially those involving galls.

Table 1 .
Synopsis of fern galls in Brazil.MG: Minas Gerais state, RJ: Rio de Janeiro state, SP: São Paulo state.