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

In a general way, galling insects can induce only one gall morphotype on the host plant species. However, some taxa of galling insects such as Eriococcidae can induce sexually dimorphic galls on the same host. In the present study, Lopesia mataybae (Diptera: Cecidomyiidae) induced two gall morphotypes on the leaflets of Matayba guianensis (Sapindaceae), a rare evidence of sexual dimorphism in galls induced by Cecidomyiidae. We investigated the adult emergence of galling insects and the morphological, histological, and histochemical attributes of the gall morphotypes. Both gall morphotypes showed the galling insect in the larval or pupal stage, and the insect adult emergence from different morphotypes was sexually distinct. Galls occupied by females (Globoid) were significantly larger (average height = 4.67 mm. S = 0.43/average width = 4.59 mm. S = 0.70) than galls occupied by males (cylindrical) (average height = 2.95 mm. S = 0.46/average width = 2.34 mm. S = 0.45). Both gall types were composed of elongated cells in the inner cortex and rounded cells in the outer cortex of the vessel-like structure. The globoid galls showed 42 cell layers (14 of them cylindrical, S = 3.86; 28 rounded, S = 5.89) and cylindrical galls showed 29 layers. There were no differences between morphotypes in the histochemical compounds detected. We have shown here significant morphological and histological differences between male and female galls possibly due to the different nutritional requirements of Lopesia mataybae sexes. Therefore, the expression of sexual dimorphism in gall morphotypes may be associated with developmental pathway differentiation between the sexes of L. mataybae.