Diverse Filters to Sense: Great Variability of Antennal Morphology and Sensillar Equipment in Gall-Wasps (Hymenoptera: Cynipidae)

Abstract

Comparative studies on antennal sensillar equipment in insects are largely lacking, despite their potential to provide insights into both ecological and phylogenetic relationships. Here we present the first comparative study on antennal morphology and sensillar equipment in female Cynipoidea (Hymenoptera), a large and diverse group of wasps, with special reference to the so-called gall-wasps (Cynipidae). A SEM analysis was conducted on 51 species from all extant cynipoid families and all cynipid tribes, and spanning all known life-histories in the superfamily (gall-inducers, gall-inquilines, and non-gall associated parasitoids). The generally filiform, rarely clavate, antennal flagellum of Cynipoidea harbours overall 12 types of sensilla: s. placoidea (SP), two types of s. coeloconica (SCo-A, SCo-B), s. campaniformia (SCa), s. basiconica (SB), five types of s. trichoidea (ST-A, B, C, D, E), large disc sensilla (LDS) and large volcano sensilla (LVS). We found a great variability in sensillar equipment both among and within lineages. However, few traits seem to be unique to specific cynipid tribes. Paraulacini are, for example, distinctive in having apical LVS; Pediaspidini are unique in having ≥3 rows of SP, each including 6–8 sensilla per flagellomere, and up to 7 SCo-A in a single flagellomere; Eschatocerini have by far the largest SCo-A. Overall, our data preliminarily suggest a tendency to decreased numbers of SP rows per flagellomere and increased relative size of SCo-A during cynipoid evolution. Furthermore, SCo-A size seems to be higher in species inducing galls in trees than in those inducing galls in herbs. On the other hand, ST seem to be more abundant on the antennae of herb-gallers than wood-gallers. The antennal morphology and sensillar equipment in Cynipoidea are the complex results of different interacting pressures that need further investigations to be clarified.

Comparison of the antennal sensilla of females of four fig-wasps associated with Ficus auriculata

“…These wasps depend largely on species-specific chemicals to discriminate their host figs from other fig species (Hossaert-Mckey et al, 2010;Proffit et al, 2007;Wang et al, 2013). These types of antennal sensilla never occur simultaneously on a single species and their types are consistent with those observed on other hymenopteran parasitoids (Amornsak et al, 1998;Basibuyuk and Quicke, 1999;Ochieng et al, 2000;Onagbola and Fadamiro, 2008;Polidori and Nieves-Aldrey, 2014;Steinbrecht, 1997;van Baaren et al, 2007). The sensilla observed on C. emarginatus were similar to those found on the closely related fig pollinating wasp C. solmsi marchali (Li et al, 2009;Meng et al, 2016).…”

“…Hair-like TS were abundant on the antennae of the four study species and have been reported on the antennae of nearly all investigated hymenopteran parasitoids (Amornsak et al, 1998;Bleeker et al, 2004;Das et al, 2011;Gao et al, 2007;Li et al, 2009Li et al, , 2014Meng et al, 2016;Ochieng et al, 2000;Onagbola and Fadamiro, 2008;Polidori and Nieves-Aldrey, 2014;Romani et al, 2010;Roux et al, 2005;van Baaren et al, 2007). In the four analysed species, the TS occur in various forms and lengths and at different locations, but they always present more longitudinal grooves on the ventral side in the direction of the antennal axis.…”

“…A wide variety of sensilla have been recorded on the antennae of female parasitoids (Basibuyuk and Quicke, 1999;Isidoro et al, 1996;Polidori and Nieves-Aldrey, 2014;van Baaren et al, 2007), and their detailed structures and configurations can help interpret sensilla function with regard to sensory-guided behaviours, such as host discrimination and exploitation (Das et al, 2011;Isidoro et al, 1996;Ochieng et al, 2000;Roux et al, 2005;Staudacher et al, 2005;van Baaren et al, 2007). There is as yet no standardised naming of sensilla and the same types of antennal sensilla are subdivided and assigned to different sensilla types by different authors despite presenting similar morphologies and distributions.…”

“…It is a multisensory detector carrying various receptors that sense a series of signals, including smell, but also taste, temperature, sound, gravity, wind speed, and even the geomagnetic field (de Oliveira et al, 2009;Isidoro et al, 1996;MeyhöFer et al, 1997;Ochieng et al, 2000;Romani et al, 2010;Staudacher et al, 2005;van Baaren et al, 2007;Zacharuk, 1985). The extent to which variation in the structure of the antennae as well as the presence and distribution of different types of sensory receptors among wasp species can be explained by differences in behaviour and oviposition strategies are poorly known (but see Polidori and Nieves-Aldrey, 2014). For fig wasps, the few studies of the sensilla on the antenna have almost exclusively focused on pollinators.…”

Anatomy of the antennal dorsal organ in female ofNeodryinus typhlocybae(Hymenoptera:Dryinidae): A peculiar sensory structure possibly involved in perception of host vibration

“…The perception of such stimuli, which can often be released in very small amounts or be biologically active for a short time, has driven the antennal sensory structures of female parasitoids toward high specialization, leading to the evolution of specific sensilla (Barlin and Vinson, ; Bin et al, ; Isidoro et al, ; Basibuyuk and Quicke, ; van Baaren et al, ; Klopfstein et al, ; Romani et al, ; Ruschioni et al, ; Polidori and Nieves‐Aldrey, ).…”