Abstract
Stylet sheath formation is a common feature among phytophagous hemipterans. These sheaths are considered essential to promote a successful feeding event. Stylet sheath compositions are largely unknown and their mode of solidification remains to be elucidated. This report demonstrates the formation and solidification of in āere (in air) produced stylet sheaths by six hemipteran families: Diaphorina citri (Psyllidae, Asian citrus psyllid), Aphis nerii (Aphididae, oleander/milkweed aphid), Toxoptera citricida (Aphididae, brown citrus aphid), Aphis gossypii (Aphididae, cotton melon aphid), Bemisia tabaci biotype B (Aleyrodidae, whitefly), Homalodisca vitripennis (Cicadellidae, glassy-winged sharpshooter), Ferrisia virgata (Pseudococcidae, striped mealybug), and Protopulvinaria pyriformis (Coccidae, pyriform scale). Examination of in āere produced stylet sheaths by confocal and scanning electron microscopy shows a common morphology of an initial flange laid down on the surface of the membrane followed by continuous hollow core structures with sequentially stacked hardened bulbous droplets. Single and multi-branched sheaths were common, whereas mealybug and scale insects typically produced multi-branched sheaths. Micrographs of the in āere formed flanges indicate flange sealing upon stylet bundle extraction in D. citri and the aphids, while the B. tabaci whitefly and H. vitripennis glassy-winged sharpshooter flanges remain unsealed. Structural similarity of in āere sheaths are apparent in stylet sheaths formed in planta, in artificial diets, or in water. The use of ‘Solvy’, a dissolvable membrane, for intact stylet sheath isolation is reported. These observations illustrate for the first time this mode of stylet sheath synthesis adding to the understanding of stylet sheath formation in phytophagous hemipterans and providing tools for future use in structural and compositional analysis.
Highlights
Many phytophagous hemipterans are characterized by common structural mouthparts [1] that penetrate host plants inter- or intra-cellularly to feed on contents of vascular tissues or other vegetative cell types
To determine if in aere stylet sheath production was an attribute of other phytophagous hemipterans, similar mock’ feeding chambers (MFC) were tested with: P. pyriformis (Figure 3A–C), F. virgata (Figure 3D–E), H. vitripennis (Figure 4A and B), B. tabaci (Figure 4E and F), and aphid (Figure 4I and J) insects with each of these produced in aere stylet sheaths
Observations indicated that D. citri, F. virgata, and P. pyriformis in aere sheaths were longer and more complex than those deposited by aphids, B. tabaci, and H. vitripennis under this artificial system
Summary
Many phytophagous hemipterans (true bugs) are characterized by common structural mouthparts [1] that penetrate host plants inter- or intra-cellularly to feed on contents of vascular tissues or other vegetative cell types. Phytophagous hemipterans feed by penetration of a stylet bundle into plant tissues. A common trait of these insects is the concurrent formation of a solidifying sheath structure (termed stylet sheath) that encapsulates the stylet bundle while they penetrate into the plant tissues. Watery and gelling (sheath) saliva represent two common forms of salivary secretions that are implicated in stylet sheaths composition and hemipteran feeding [8,9,10,11,12,13,14,15]. The exact function(s) of the stylet sheath in feeding are not known; trait conservation across phytophagous hemipterans [5], implies biological importance. Stylet sheaths are thought to provide stability and directional orientation to the stylets during the piercing process [16], to aid in proper feeding [16], to ‘cloak’ the stylets from host (plant) defense responses [9], and to seal up cell damage caused by stylet probing [17,18]
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