Research Article |
Corresponding author: Matthias Schindler ( m.schindler@uni-bonn.de ) Academic editor: Michael Ohl
© 2018 Matthias Schindler, Michaela M. Hofmann, Dieter Wittmann, Susanne S. Renner.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Schindler M, Hofmann MM, Wittmann D, Renner SS (2018) Courtship behaviour in the genus Nomada – antennal grabbing and possible transfer of male secretions. Journal of Hymenoptera Research 65: 47-59. https://doi.org/10.3897/jhr.65.24947
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Due to low population densities, copulation in the cuckoo bee genus Nomada has not previously been observed, although a seminal paper by
Antennal structure, copulation, chemomimesis, male secretions, cuckoo bees
Bees (Apoidea, Apiformes) use visual, auditory and chemical signals to locate potential mates, and males may search for females at flowers, nest sites, or perch spots by non-aggressively patrolling along a strict route or by defending a territory in which females are likely to be encountered (
Nomada parasitizes predominantly species of Andrena (
The present study of the courtship and mating behaviour of Nomada is based on field and lab observations of N. fucata and N. lathburiana in central Germany (
Courtship behavior in Nomada fucata F. and N. lathburiana (K.) was studied both in the field and in the lab. The courtship phase was observed at nesting sites of the host species Andrena flavipes Panz. and A. vaga Panz. and at foraging plants in an abandoned gravel pit near Bonn (50.773293°N, 7.147145°E, about 50 m a.s.l.) in 1998 and 1999. The initiation and insertion phase of copulation in N. flavoguttata (K.) was observed on 24 May 2017 in the conservation area “Allacher Heide” in Munich (48.206729°N, 11.474383°E, 517 m a.s.l.). It was the first sunny and warm day after a longer period of cold and moist weather, leading to a major hatching event of several Nomada species. Within 5 m2, more than 50 Nomada bees could be observed foraging and mating on Taraxacum officinales.l. (Fig.
Mating of Nomada lathburiana (a, b) in the lab and of N. flavoguttata on Taraxacum officinale s.l.. (c, d). a ♂ mounts the ♀ and fixes its wings with its mid and hind legs and tries to entangle the female´s antennae spirally with its flagella. ♂ lifts the abdomen of the ♀ with its hind legs and tries to insert its genitalia in the female´s genital opening b ♂ repeatedly spirally entangles the female´s antennae with its left and right flagellum and pulls it off medially to apically. ♂ tries to insert its genitalia repeatedly c ♂♂ patrolling at a blossom of T. officinale d Insertion phase of copulation. Antennation of ♂ as described in (b).
Studies in the lab were carried out with virgin males and females of N. fucata and N. lathburiana. Bees were collected with emergence traps at the nests and released in flight cages (4 × 2 × 2 m) or transferred in petri-dishes (ø 15 cm) for observation. Nomada individuals were kept in refrigerators at 6 °C before being placed into the arena. Petri-dishes were illuminated with artificial light. Courtship behavior was documented with macro photographs and video records that were then analyzed frame by frame. Courtship was divided into the following phases, a) Courtship or pre-copula phase: males discovering mates, males approaching females, males mounting the abdomen of the females and attempting to copulate. b) Copula phase: male inserting his genital into the female’s genital aperture. We did not observe the separation phase of copulation.
Flagella morphology of males of Nomada fucata and N. lathburiana was studied under a photo stereomicroscope, with photos taken at 10 to 40 x. Morphological terminology for the antennae follows
Antennae of males of N. fucata and N. lathburiana were fixed in a Duboscq-Brasil solution (
Field observations revealed that males of N. fucata patrol together with males of Andrena flavipes, the host species, at foraging plants and above the entrances of the fossorial host nests. During these flights, we observed neither inter- nor intraspecific aggression. Nomada males attempted to copulate with females that they discovered on flowers or on the ground, but females rejected the males in all observed attempts (n = 11). Males of N. lathburiana did not patrol potential rendezvous sites.
For both N. fucata and N. lathburiana, copulation was studied in the laboratory, with females chilled down for immobilization (since mobile females repelled the males in the lab experiment). For N. fucata, two copulations were observed, and for N. lathburiana four. Males mounted the abdomen of the females, fixed their forelegs on the side of the females’ thorax, clinched the wings of the females with their middle legs and lifted their mates’ abdomen with their hind legs to insert the genitalia. In this position the males’ head was above the pronotum of the female. During the initiation of copulation males repeatedly wound their flagella (in case of N. lathburiana in a spiral) around the female’s antennae and then stroked the female’s antennae (Fig.
Mating of Nomada fucata (singular images of a video sequence). a ♂ mounts the ♀ and fixes its wings with its mid and hind legs. ♂ lifts the abdomen of the ♀ with its hind legs and tries to insert its genitalia in the female´s genital opening b ♂ entangles the female´s left antenna with its left flagellum c ♂ pulls its left flagellum from medial to apical along the female antenna d ♂ repeatedly entangles the female´s antennae with its left and right flagellum and pulls it off medially to apically. ♂ tries to insert its genitalia.
In all three species, the flagella of the males’ antennae bear tyloid like-structures (Table
Modifications on the antennae of Nomada fucata ♂ (a) (left antenna, dorsal), N. flavoguttata ♂ (b) (right antenna, ventral) and N. lathburiana ♂ (c) (left antenna, lateral). SEM micrographs. a1 weak elevation on flagellum 6 laterally. Scale unit: 0.1 mm b1 weak elevations on flagellum 4 ventrally. Scale unit: 0.1 mm c1 nodule on flagellum 9. Scale unit: 0.1 mm a2 pores and secretions on the elevation. Scale unit: 0.01 mm b2 pores and setae on the elevations. Scale unit: 0.01 mm c2 nodule covered with secretions. Scale unit: 0.02 mm.
Tyloid-like structures on the flagella of central-European Nomada males. The preselection of most species followed descriptions from
Species | Species-group | Tyloid-like structures | |
---|---|---|---|
position | morphology | ||
N. bifasciata Olivier | bifasciata-gr. | figs 3–8 | inconspicuous tubercles |
N. fucata Panzer | bifasciata-gr. | figs 3–8 | inconspicuous tubercles |
N. melanopyga Schmied. | bifasciata-gr. | figs 4–9 | inconspicuous tubercles |
N. succincta Panzer1 | bifasciata-gr. | figs 3–8 | inconspicuous tubercles |
N. flavoguttata (Kirby) | flavoguttata-gr. | figs. 3–7 | inconspicuous tubercles |
N. bluethgeni Stöckhert | furva-gr. | figs 2–4 | spiky spots |
N. distinguenda Morawitz | furva-gr. | figs 3–5 | inconspicuous tubercles |
N. furvoides Stöckhert | furva-gr. | figs 3–5 | spiky to rounded elevation |
N. kohli Schmied. | furva-gr. | figs 3–5 | rounded spots |
N. posthuma Blüthgen2 | c.f. furva-gr. | figs 3–6 | spots |
N. argentata Herr.-Schäf. | integra-gr. | figs 4–8 | tubercles |
N. beaumonti Schwarz | integra-gr. | figs 4–10 | spiky spots |
N. facilis Schwarz | integra-gr. | figs 3–9 | spiky spots |
N. integra Brullé | integra-gr. | figs 3–10 | transverse ridges |
N. pleurosticta Herr.-Schäf. | integra-gr. | figs 4–9 | transverse ridges |
N. stigma Fabricius | integra-gr. | figs 4–9 | transverse ridges |
N. braunsiana Schmied. | ruficornis-gr. | figs 2–9 | spots |
N. castellana Dusmet | ruficornis-gr. | figs 4–12 | spots |
N. lathburiana (Kirby) | ruficornis-gr. | figs 1–11 | thorn-like spots |
N. striata Fabricius | ruficornis-gr. | figs 3–7 | inconspicuous tubercles |
Histological studies of N. fucata and N. lathburiana corroborated that these antennal modifications are associated with glands (Fig.
Semi-thin sections of antennomere 9 of Nomada lathburiana ♂ [a=longitudinal, b=cross. Ty=Thyloid, C1=compact epidermal cells, C2= gland cells, type III (Noirot & Quennedey 1991). Scale unit: 0.05 mm (a1, b1, b2), 0.02 mm (a2). Topography: l=lateral, m=medial, v=ventral, d=dorsal] and of antennomere 7 of Nomada fucata ♂ [c=cross. Ty=Tyloid, C1= compact epidermal cells, C2=gland cells, type III, P=porous cuticle (Noirot & Quennedey 1991). Scale unit: 0.05 mm (c1, c2) Topography: l=lateral, m=medial, v=ventral, d=dorsal].
This is the first report of the mating behavior in Nomada. The males use their antennae to grab the females’ antennae for a chemical signal transfer, while they use their feet to pin down the female. In Hymenoptera and other insects, transfer of sexual pheromones from the males to the females is widespread (e.g. Hymenoptera, Terebrantes:
Male antennation has been interpreted in terms of sensory exploration of visual and tactile stimuli as well as the transfer of pheromones (
The biological function of the substance transferred by Nomada males to females during antennal grabbing may lie in making inseminated females unattractive to other males as suggested for Centris adani (
Constructive comments from the editor, Michael Ohl, an anonymous reviewer, and Gunnar Bergström are much appreciated.
DNA extraction, amplification and sequencing
DNA was isolated with the QIAGEN DNeasy-Blood & Tissue Kit (Qiagen GmbH, Hilden, Germany), using one leg per bee and following the QIAGEN Quick-Start Protocol (January 2011) with two modifications: The legs were incubated in Lysis Buffer (ATL) and Proteinase K for at least 48 h at room temperature and 5 to 10 hours at 56 °C. To increase DNA concentration, we used 100 μL elution buffer (PE; 5 mM Tris/HCL pH 8.5). A fragment of the mitochondrial cytochrome c oxidase (COI) gene with a 658 bp target region near the 5´terminus of COI was amplified using primers described in Schmidt et al. (2015), namely COIfor (ATT CAA CCA ATC ATA AAG ATA TTG G) and COIrev (TAA ACT TCT GGA TGT CCA AAA AAT CA). Polymerase chain reactions (PCR) were performed using standard conditions. Amplified products were sequenced on an ABI 3100 Avant capillary sequencer (Applied Biosystems), and forward and reverse sequences were manually edited and assembled,using Sequencher 5.1 (Gene Codes Corporation, Ann Arbor, Michigan, USA) and BLAST searching in GenBank. All species sequenced for this study have been previously barcoded for the GBOL-project, and reference sequences were therefore available in NCBI GenBank under DOIs: doi.org/10.5883/DS-GBAPI and dx.doi.org/10.5883/DS-GBAPS. Three new sequences were generated for this study and are available under as GenBank accessions MG845937, MG845938, and MG845939.
Schmidt S, Schmid-Egger C, Morinière J, Haszprunar G, and Hebert PDN (2015) DNA barcoding largely supports 250 years of classical taxonomy: identifications for Central European bees (Hymenoptera, Apoidea partim). Molecular Ecology Resources 15: 985–1000.