Morphological and histological characterization of extrafloral nectaries induced by Coelocephalapion galls on Croton antisyphiliticus in the Brazilian Cerrado

Abstract In the Brazilian Cerrado, Coelocephalapion weevils induce galls on the leaves of Croton antisyphiliticus (Euphorbiaceae). Gall induction results in dozens of extrafloral nectaries (EFNs) being produced on the gall surface. This plant has a low number of EFNs at the margin of its healthy leaves. The interaction weevil-plant induces the overproduction of EFNs on the galls. The presence of glands on leaves and galls in the same plant is a rare condition in nature. We examined the EFNs on young and old leaves and on the surface of young and old galls, and described the trichomes and stomata on leaves and galls on C. antisyphiliticus. To measure the differences in structures we used digital photographs and standard scanning electron microscopy. Two-way ANOVA and post hoc Tuckey tests were used to compare their number and size of EFNs. We found more EFNs on galls than on leaves. No stomata or trichomes were found on the EFNs surface. The size and shape of the secretory EFNs heads on leaves and galls were different. Trichome density was higher on young and mature galls than on leaves. Trichome secretory heads on leaves are concave, while those on galls are convex. The nuclei of the EFNs epidermal cells of the leaf blade margin occupy smaller areas than those of the petiole and young galls. This study highlights the potential of gall traits that might increase plant defense against galling insects through the overproduction of these glands.