Stylet Morphometrics and Citrus Leaf Vein Structure in Relation to Feeding Behavior of the Asian Citrus Psyllid Diaphorina citri, Vector of Citrus Huanglongbing Bacterium

Abstract

The Asian citrus psyllid (ACP), Diaphorina citri (Hemiptera: Psyllidae), is the primary vector of the phloem-limited bacterium Candidatus Liberibacter asiaticus (LAS) associated with huanglongbing (HLB, citrus greening), considered the world’s most serious disease of citrus. Stylet morphometrics of ACP nymphs and adults were studied in relation to citrus vein structure and to their putative (histologically verified) feeding sites on Valencia orange leaves. ACP nymphs preferred to settle and feed on the lower (abaxial) side of young leaves either on secondary veins or on the sides of the midrib, whereas adults preferred to settle and feed on the upper (adaxial) or lower secondary veins of young or old leaves. Early instar nymphs can reach and probe the phloem probably because the distance to the phloem is considerably shorter in younger than in mature leaves, and is shorter from the sides of the midrib compared to that from the center. Additionally, the thick-walled ‘fibrous ring’ (sclerenchyma) around the phloem, which may act as a barrier to ACP stylet penetration into the phloem, is more prominent in older than in younger leaves and in the center than on the sides of the midrib. The majority (80–90%) of the salivary sheath termini produced by ACP nymphs and adults that reached a vascular bundle were associated with the phloem, whereas only 10–20% were associated with xylem vessels. Ultrastructural studies on ACP stylets and LAS-infected leaves suggested that the width of the maxillary food canal in first instar nymphs is wide enough for LAS bacteria to traverse during food ingestion (and LAS acquisition). However, the width of the maxillary salivary canal in these nymphs may not be wide enough to accommodate LAS bacteria during salivation (and LAS inoculation) into host plants. This may explain the inability of early instar nymphs to transmit LAS/HLB in earlier reports.

Colonization and Intrusive Invasion of Potato Psyllid by ‘Candidatus Liberibacter solanacearum’

“…The diameters of the different nymphal instar stylet bundle food canals are expected to become consecutively larger with each (increasing) developmental stage. The diameter of the adult stylet food canal has been estimated by TEM as approximately 0.818 µm (Ammar et al 2013), 0.6 µm (Cicero et al 2015), and 0.9 µm (Garzo et al 2012). Given this range in size, a predicted minimum threshold diameter by which CLso ingestion could occur would seem possible after stylet biogenesis during the pharate third instar.…”

Sclerenchymatous ring as a barrier to phloem feeding by Asian citrus psyllid: Evidence from electrical penetration graph and visualization of stylet pathways

“…citri nymphs and adults that reached a vascular bundle were associated with the phloem, whereas 10–20% were associated with xylem vessels [15]. A fibrous ring of thick-walled sclerenchyma fibers around the phloem in citrus leaves was shown to be more prominent (thicker, with more layers) in fully expanded mature leaves compared with younger leaves, especially on the lower (abaxial) side compared with the adaxial side, and in the midrib compared with secondary veins [15]. In a subsequent study [16], the fibrous ring in the midrib was found to be significantly thicker in one citrus accession (UN-3881) that is relatively resistant to D .…”

Calosa y especies reactivas de oxígeno expresadas en hojas de caña de azúcar por daño mecánico de mosca pinta

“…La respuesta a estos ataques del insecto requiere un mecanismo integrado donde las señales internas y externas de la planta detectan y ocasionan una reacción apropiada en la planta (Stepanova et al, 2005). El insecto en estado de ninfa y adulto se caracteriza por tener un estilete que inserta en la lámina foliar para alimentarse, lo que provoca daño celular con la fractura inter e intracelular (daño mecánico) que induce estrés biótico (Ammar et al, 2013).…”

“…Estos procesos de defensa se han estudiado en diversos modelos, algunos en cítricos donde estudian el daño causado por el estilete de las ninfas de Diaphorina citri, que es el sitio de alimentación (Ammar et al, 2013). En el caso de las gramíneas existen estudios en maíz donde se observó la acumulación de calosa por presencia de aluminio debido a la exposición que tienen las raíces a dicho elemento que les induce la expresión de un daño (Arcos y Narro, 2009).…”