ANATOMICAL AND HISTOCHEMICAL EFFECTS OF FEEDING BY CITRUS LEAFMINER LARVAE (PHYLLOCNISTIS-CITRELLA STAINTON) IN CITRUS LEAVES

Young expanding leaves of 'Ambersweet' [Citrus reticulata Blanco x C. paradisi Macf. x C. reticulato.) x C. sinensis (L) Osb.] with feeding injury by third larval stage of citrus leafminer (Phyllocnistis citrel la) were examined by light and electron microscopy for extent of injur y and tissue recovery over time. Results confirmed that injury is conf ined to the epidermal layer, leaving a thin covering over the mine tun nel that consisted of the cuticle and outer cell wall. Wound recovery consisted of two possible responses: the production of callus tissue o r the formation of wound periderm. The production of callus tissue dev eloped within 3 days of injury when the uninjured palisade or spongy p arenchyma below the injured epidermis produced callus tissue through p ericlinal or diagonal cell divisions. After 1 month, the entire epider mis was replaced by callus tissue. In the absence of secondary microbi al invasion, this callus tissue developed a thick cuticle, followed by development of a covering of platelet wax after 4 months. Alternative ly, wound periderm formed if the outer cuticular covering was torn bef ore the cuticle had developed sufficiently to prevent the exposed cell s from being desiccated or invaded by fungi, bacteria, or other insect s. The wound periderm consisted of a lignified layer of collapsed call us cells, a suberized phellem layer, and a multilayered phelloderm-phe llogen. Since there were always cellular collapse or fungi and bacteri a associated with wound periderm formation, it was determined to be a secondary effect, not a direct effect of leafminer feeding.