Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/22/2013
Publication Date: 4/24/2013
Citation: Morgan, J.K., Luzio, G.A., Ammar, E., Hunter, W.B., Hall, D.G., Shatters, R.G. 2013. Formation of stylet sheaths in aere (in air) from eight species of phytophagous hemipterans from six families (suborders: Auchenorrhyncha and Sternorrhyncha). PLoS ONE. 8(4):e62444. Interpretive Summary: A common trait of plant feeding insects from the order Hemiptera is to form stylet sheath structures as they penetrate a plant to feed. These structures are created as the insect inserts its stylet into the leaf tissue and while penetrating it secretes a liquid material that hardens forming a surrounding structure encasing the stylet within the leaf tissue. These sheath structures are thought to provide the stylet with structural stability, directional orientation to aid in proper feeding, and to cloak the stylet from the natural plant defense responses as it penetrates and resides within the leaf tissue. A common held belief is that these stylet sheaths require plant molecular interactions to form these solid sheath structures. We here show that stylet sheath structures are made in air without the need of plant interaction for secretion and solidification. We show this trait to occur with various economically important hemipteran pests including: psyllid, aphid, mealybug, leafhopper, whitefly, and scale insects. Using a new technique (that we discovered) using 'mock feeding' (without food) chambers we were able to take real-time video, photo, and microscopic images of these structures for these various insects. The solidification of the sheaths themselves is very rapid (~45 seconds from liquid to solid state). Also, using a dissolvable membrane (Solvy) we were able to isolate the complete sheath structures for imaging and for use in other analyses. Our imagery of 'in air' formed sheaths when compared to 'in leaf' formed sheaths indicate that the air formed sheath structures appear to be very similar to sheaths formed within the leaf tissues. These results help to further advance our understanding of the stylet sheaths and help us to better understand the feeding process of these important insect pests.
Technical Abstract: Stylet sheath formation is a common feature among phytophagous hemipterans. These sheaths are considered essential to promote a successful feeding event of these piercing-sucking insects. The stylet sheath composition is unknown, and it is suggested that it forms through interactions with external (host plant) molecules. This report demonstrates for the first time, that stylet sheaths form and solidify in air (in aere) without plant or diet interaction by six hemipteran families: Diaphorina citri (Psyllidae, Asian citrus psyllid), Aphis nerii (Aphididae, oleander/milkweed aphid), Toxoptera citricidus (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 aere formed stylet sheaths by confocal and scanning electron microscopy, shows a common morphology of 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 flange region show flange sealing upon stylet bundle extraction for both psyllids and aphids, while whitefly and glassy-winged sharpshooter flanges remain unsealed. Structural similarity of in aere sheaths appear in common to stylet sheaths found in planta and in artificial diets. The use of ‘Solvy’, a dissolvable membrane, for intact (complete) stylet sheath isolation is reported. These observations show for the first time this mode of stylet sheath synthesis expanding the understanding of stylet sheath formation in phytophagous hemipterans.