As soft as silk: structural and chemical traits can help with the identification of Niphidium crassifolium (Polypodiaceae) gall inducers

Abstract

Ferns have been poorly reported as hosts of gall inducers, and their multitrophic interactions and relationships are practically unknown to science. We focused on Niphidium crassifolium (Polypodiaceae) that hosts globoid leaf galls. The galls on N. crassifolium have only reported for the South and Southeast regions of Brazil, with a discussion regarding the identity of the gall inducer: is it a Cecidomyiidae-Diptera or to Coccidae-Hemiptera? These two insect groups have distinct characteristics and consequently their galls must have distinct anatomical and histochemical traits. Such traits may work out as functional tools to be used to confirm the taxa of the associated galling herbivore and to evaluate their geographic distribution. Our study aimed to expand the known distribution of N. crassifolium and its interactions based on an inventory of scientific articles and on herbarium data, and also to test the usefulness of anatomical and histochemical traits for proposing the identity of the gall inducer. The geographic distribution of N. crassifolium galls involves five South American countries, i.e., Bolivia, French Guiana, Guyana, Peru, and Brazil. The development of an outer tissue compartment with phenolic-rich cell layers and an inner nutritive tissue leads us to infer that the inducer belongs to the Cecidomyiidae family.