The influence of parasitoidism on the anatomical and histochemical profiles of the host leaves in a galling Lepidoptera - Bauhinia ungulata system

Abstract

Galls induced by insects develop through a complex series of plant cell responses. Bauhinia ungulata L. (Fabaceae: Caesalpinioideae) has leaf-folding galls, which were studied by means of anatomical and histochemical approaches. These approaches compared the non-galled leaves, non-parasitoidized galls, and parasitoidized galls by addressing two questions: (1) what structural and histochemical changes are caused by the gall inducer in the leaf tissues of the host plant? And (2) is the parasitoid capable of affecting the gall structure? The non-galled leaf is amphistomatic, with anomocytic stomata, and multicellular non-glandular and navicular glandular trichomes. The mesophyll is dorsiventral, and the vascular system is surrounded by a lignified bundle sheath. In the gall, the outer epidermis is derived from the abaxial leaf epidermis. The outer cortex of the gall originates from the chlorophyllian parenchyma, and is homogeneous, with polyhedral cells and few intercellular spaces. The vascularization net is enhanced, and the secondary veins are disorganized. The nutritive tissue derives from the cells of the adaxial epidermis and adjacent parenchyma, which accumulate lipids, and is partly consumed by the chewing larvae. The cells of the outer cortex and those around the vascular bundles accumulate secondary metabolites, functioning as protective layers against natural enemies. The parasitoidized galls are similar to the non-parasitoidized ones, except for the sites of intact hyperplasic nutritive tissue with hypertrophied cells, which are visible macroscopically. This indicates the continued stimuli from the Lepidoptera feeding on the host-plant cells, which continue to enlarge, but will no longer be used for larvae nutrition.