Species- and Sex-Specific Distribution of Antennal Olfactory Sensilla in Two
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Micron 106 (2018) 7–20 Contents lists available at ScienceDirect Micron journal homepage: www.elsevier.com/locate/micron Species- and sex-specific distribution of antennal olfactory sensilla in two T tortricid moths, Epiphyas postvittana and Planotortrix octo ⁎ Gwang Hyun Roha, Kye Chung Parkb, Hyun-Woo Ohc, Chung Gyoo Parka,d, a Institute of Agriculture and Life Science, Gyeongsang National University, Jinju 52828, Republic of Korea b New Zealand Institute for Plant and Food Research, Christchurch, New Zealand c Korea Research Institute of Bioscience & Biotechnology, Daejeon 34141, Republic of Korea d Institute of Life Science (BK21+ Program), Gyeongsang National University, Jinju 52828, Republic of Korea ARTICLE INFO ABSTRACT Keywords: We investigated the morphology and distribution of antennal sensilla in males and females of two tortricid Antenna moths, Epiphyas postvittana and Planotortrix octo, by scanning electron microscopy. The number and overall Morphology length of flagellomeres were significantly greater in females than in males in both species. The antennae of each Olfaction species bearing six morphological types of sensilla (trichodea, basiconica, coeloconica, auricillica, chaetica, and Scanning electron microscopy styloconica), with different numbers and distributions along the antennae. Among these sensilla, four types Sensilla (trichodea, basiconica, coeloconica, and auricillica) displayed multi-porous cuticular surfaces, indicating that Trichodea their primary sensory function is olfactory. Each of these four types of sensilla could be further classified into subtypes according to their size, shape, and surface structure. Both E. postvittana and P. octo exhibited sexual dimorphism of the profiles of antennal olfactory sensilla. Trichoid sensilla were the most abundant type in both species. Subtype I trichoid sensilla were male-specific in both species, indicating that they are responsible for the perception of conspecific female sex pheromone. By contrast, subtype II trichoid sensilla were more abundant in female antennae in both species, suggesting that some subtype II trichoid sensilla are involved in female-specific behaviors, such as oviposition. Chaetic and styloconic sensilla displayed relatively even distributions along the antennae. Our results indicate that the antennae of E. postvittana and P. octo have species-specific and sex-specific profiles of olfactory sensilla. The morphological information obtained in our study provides a basis for elec- trophysiological and behavioral studies of the olfactory sensory function of each morphological type of sensilla. 1. Introduction sensory modalities are often related to the purpose of sensory reception, such as finding host plants and mates of a particular species (Cossé Antennae are the major sensory organs in insects, bearing various et al., 1998; Baker et al., 2004; Ansebo et al., 2005; Pophof et al., 2005; types of sensilla for the detection of chemical and physical sensory cues Sun et al., 2011). The morphology and distribution of antennal sensilla from the surrounding environment. Each sensillum is an independent are often characteristic features of a specific group of insects and can be sensory unit containing sensory neurons, auxiliary cells, and various used for taxonomic identification (Notaro-Muñoz et al., 1997; Molero- extracellular components, and these components are spatially and Baltanás et al., 2000). The morphological identification of sensilla with physiologically isolated from the outside of the sensillum (Steinbrecht, specific sensory modalities can provide valuable information for sub- 1997). sequent electrophysiological or behavioral studies of the functions of These antennal sensilla display diverse morphological features, and sensilla (Baker et al., 2004; Malo et al., 2004; Pophof et al., 2005; Sun the specific external shape and morphological characters are typically et al., 2011). related to the sensory functions of sensilla. For example, thick and long Olfactory sensilla are the most abundant type of sensilla in the an- setae with basal sockets and no surface pores are typical features of tennae of many groups of insects, such as flies (Stocker, 2001; mechanosensilla, the presence of one or a few pores at the tip indicates Sukontason et al., 2004), beetles (Merivee et al., 2002; Ploomi et al., a gustatory function, and the presence of numerous nanoscale pores 2003), bees (Frasnelli et al., 2010), and moths (Gómez et al., 2003; throughout the cuticular surface suggests an olfactory function Gómez and Carrasco, 2008; Sun et al., 2011). These antennal olfactory (Zacharuk, 1980). The presence and abundance of sensilla with specific sensilla display distinct shapes, such as trichoid (long hair with a sharp ⁎ Corresponding author at: Institute of Life Science, Gyeongsang National University, Jinju 52828, Republic of Korea. E-mail address: [email protected] (C.G. Park). https://doi.org/10.1016/j.micron.2017.12.006 Received 12 September 2017; Received in revised form 15 December 2017; Accepted 18 December 2017 Available online 21 December 2017 0968-4328/ © 2017 Elsevier Ltd. All rights reserved. G.H. Roh et al. Micron 106 (2018) 7–20 tip), basiconic (short hair with a blunt tip), auricillic (rabbit ear shape), 2.2. Scanning electron microscopy placoid (round dome shape), and coeloconic (short peg with long- itudinal grooves). Despite the diverse shapes, all types of olfactory For scanning electron microscopy, antennae of adult moths were sensilla, except coeloconic sensilla, have numerous nanoscale pores excised at the base around the scape and fixed in 70% ethanol for ap- (approximately 20–50 nm in diameter) on their cuticular surface proximately 24 h. The antennae were then dried in closed plastic con- (Onagbola and Fadamiro, 2008; Kim et al., 2016; Roh et al., 2016; Wee tainers with desiccants and mounted on a piece of double-sided sticky et al., 2016). Instead, coeloconic sensilla possess longitudinal grooves tape attached to the top of aluminum specimen stubs. The samples were running along the sensory peg (Faucheux et al., 2006; Diongue et al., then gold-coated in a sputter coater (Q15ORS; Quorum, Lewes, UK). 2013; Roh et al., 2016). These pores and grooves appear to be the en- The antennal preparations were observed using two different scanning trance for odor molecules into the olfactory sensillum before reaching electron microscopes (JCM-5000, JEOL, Tokyo, Japan; FEI Quanta 250 their corresponding receptors on dendritic membranes through the FEG, FEI, Hillsboro, OR, USA) at 10 kV. sensillum lymph (Steinbrecht, 1997; Shields and Hildebrand, 1999). Different insect species belonging to the same group appear to share 2.3. Identification of olfactory sensilla and classification into morphological similar types of olfactory sensilla, although the detailed morphological types properties of sensilla can be species-specific. For example, elongated placoid sensilla are typical olfactory sensilla in hymenopteran species After counting the flagellomeres in male and female antennae of E. (Gao et al., 2007; Onagbola and Fadamiro, 2008), round placoid sen- postvittana and P. octo, the sensilla present in the 1st, 6th, 11th, 21th, silla are typical in homopteran species (Broeckling and Salom, 2003), 31th, and 41th flagellomeres were examined at low magni fications of short basiconic and auricillic sensilla are typical in dipteran species under × 5000. These sensilla were then classified into distinct groups, (Ilango et al., 1994; Sukontason et al., 2004, 2007), and long trichoid such as trichodea, basiconica, coeloconica, auricillica, chaetica, and sensilla are typical in moths (Diongue et al., 2013; Roh et al., 2016). styloconica, according to their gross morphology at low magnification. The light brown apple moth Epiphyas postvittana and the green- The sensilla belonging to each group were randomly sampled and ex- headed leafroller moth Planotortrix octo are polyphagous tortricid amined at high resolution, up to × 50,000, in which the detailed moths endemic to Australia and New Zealand (Danthanarayana, 1975; structures of the cuticular surfaces of sensilla were carefully examined. Suckling and Brockerhoff, 2010). Although they are polyphagous, fe- When numerous pores with diameters of 20–50 nm were present on the male moths of each species demonstrate preferences and aversions to- sensillum surface, the sensilla were regarded as olfactory. Peg-shaped wards distinct groups of plants for oviposition (Wearing et al., 1991; sensilla (coeloconica) with narrow longitudinal grooves were also re- Mclaren and Suckling, 1993; Suckling et al., 1998; Suckling and garded as olfactory. Then, the sensilla in each group were further Brockerhoff, 2010; Brockerhoff et al., 2011), indicating that female classified into subtypes based on their size, the presence of a basal moths process plant volatile cues via the olfactory sensory system. Both socket, and surface morphology. The sizes (length and width) of fla- E. postvittana and P. octo use multi-component female sex pheromones, gellomeres and sensilla were measured using ImageJ (Rasband, suggesting the presence of male-specific ORNs (olfactory receptor 1997–2006). The overall length and total number of flagellomeres on a neurons) for the detection of conspecific female sex pheromone com- flagellum were measured for five male and five female antennae in the ponents. Recent molecular studies have revealed the sex-biased ex- two species. pression of odorant receptors in the antennae of E. postvittana (Corcoran et al., 2015) and P. octo (Steinwender