The “acrostyle”: A newly described anatomical structure in aphid stylets Marilyne Uzest a , Daniel Gargani a , Aviv Dombrovsky b , Chantal Cazevieille c , Didier Cot d , Stéphane Blanc a, * a UMR BGPI, INRA/CIRAD/AgroM, TA A54/K, Campus International de Baillarguet, 34398 Montpellier Cedex 05, France b Agricultural Research Organization e the Volcani Center, P.O.B. 6, Bet-Dagan, 50250 Israel c Centre Régional d'Imagerie Cellulaire/Institut Universitaire de Recherche Clinique, 34093 Montpellier, France d Institut Européen des Membranes, UMR 5635, 34095 Montpellier Cedex 05, France article info Article history: Received 25 November 2009 Accepted 10 February 2010 Keywords: Aphid Maxillary stylets Transmission electron microscopy Scanning electron microscopy Cuticular protein Virus transmission abstract The recent demonstration that a plant virus could be retained on protein receptors located exclusively in a small area inside the common duct at the tip of aphid maxillary stylets indicated the possible existence of a distinct anatomical structure at this level. Since no distinct feature within the common duct of any aphid species has ever been reported in the literature, we first carefully re-examined the distal extremity of the maxillary stylets of Acyrthosiphon pisum using transmission- and scanning-electron microscopy. Here, we describe an area of the cuticle surface displaying a different structure that is limited to a “band” paving the bottom of the common duct in each opposing maxillary stylet. This band starts at the very distal extremity, adopts a “comma-like” shape as it continues up towards the salivary canal, reducing in width and disappearing before actually reaching it. Investigations on several aphid species led to the conclusion that this anatomical featuredwhich we have tentatively named the “acrostyle”dis highly conserved among aphids. We then produced an antibody recognizing a consensus peptide located in the middle of the RR-2 motif of cuticular proteins from A. pisum and showed that this motif is accessible specifically within the acrostyle, indicating a higher concentration of cuticular proteins. While it is clear that at least some viruses can use the acrostyle to interact with their aphid vectors to ensure plant- to-plant transmission, the role of this new “organ” in aphid biology is unknown and calls for further investigation in the near future. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Aphids have long been the subject of intense research for several reasons: (1) they cause important economic losses; (2) they have adopted a complex life cycle with alternating asexual and sexual phases; (3) they show remarkable phenotypic plasticity; and finally (4) they transmit hundreds of plant pathogens, mostly viruses. These diverse features have motivated research interest in the anatomy, physiology, population genetics and functional genomics of aphids. Notably, the capacity for virus transmission has engen- dered much research on aphid feeding behavior in conjunction with a very detailed analysis of the anatomy and ultrastructure of aphid stylets. Aphids are insects with piercing-sucking mouthparts composed of a short and triangular labrum, which covers the base of the stylet bundle, the labium, which is a segmented and tubular organ with complex musculature that contracts and shortens during insertion of the stylet into plant tissue, and the stylet bundle inserted in a groove dug along the length of the anterior surface of the labium. This bundle comprises two external mandibular stylets that surround and protect two inner maxillary stylets, all transformed into four long needle-like cuticle structures, several hundred microns in length (typically 400e700 mm) and slightly enlarged at the base coming from the head capsule. Only the mandibular stylets are innervated by two dendrites present in a small internal duct (Forbes, 1966). Their distal extremity is curved inward and sharpens at the tip, the outer surface harboring a series of barb-like ridges (Forbes, 1969; van Hoof, 1958) that play a role during insertion of the bundle into the plant, lacerating tissues and, together with a clamping action by the tip of the labium, probably anchoring the stylets between thrusts (Forbes, 1966; Klingauf, 1987). Maxillary stylets are also sharply pointed at the distal extremity, but they display a much more complex architecture (a graphical representation of the stylet bundle is presented in Fig. 1). The whole length of the inner face of both maxillary stylets is sculpted by longitudinal ridges and grooves, interlocking in a “zip-lock” * Corresponding author. Tel.: þ33 4 99 62 48 04; fax: þ33 4 99 62 48 22. E-mail address: blanc@supagro.inra.fr (S. Blanc). Contents lists available at ScienceDirect Arthropod Structure & Development journal homepage: www.elsevier.com/locate/asd 1467-8039/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.asd.2010.02.005 Arthropod Structure & Development 39 (2010) 221e229