Sexually dimorphic galls induced on leaflets of Matayba guianensis (Sapindaceae): a rare phenomenon occurring in Diptera (Cecidomyiidae)

Abstract

Galls are formed from chemical and/or mechanical stimuli from different organisms, especially insects that establish extremely specific relationships with their host plants. However, some species are capable of inducing different morphotypes of galls in the same host plant, with morphological, anatomical, histochemical and phytochemical differences, and these characteristics may be related to the sexual dimorphism of the galling insect. Galling insects are considered true manipulators of the host plant phenotype, altering the host tissues and their composition for their own benefit. The objective of this work was to investigate the possible morphological, anatomical and compositional differences of two morphotypes of galls induced by Lopesia mataybae on leaflets of Matayba guianensis, through anatomical and histocytometric analyses. Adult galling insects hatched from different morphotypes, females hatched from the globoid morphotype and males hatched from the cylindrical morphotype. Galls occupied by females (average height =4.67 mm. S=0.43/average width=4.59 mm. S= 0.70) were significantly larger than galls occupied by males (average height=2.95 mm. S=0.46/average width= 2.34 mm. S= 0.45). Both morphotypes, globoid and cylindrical, are composed of elongated cells in the inner parenchyma and rounded cells in the outer parenchyma. There was no difference in the histochemical compounds detected. In this work, the morphological and histological importance between galls occupied by males and females was elucidated, possibly as a result of different nutritional requirements of the sexes of Lopesia mataybae. Therefore, the expression of sexual dimorphism in gall morphotypes may be associated with the differentiation of developmental pathways between the sexes of L. mataybae, including the structure and modification of cell wall compounds and possible differences in the amount of phytohormones to which need to be investigated.