Original article

Why males of leafcutter bees hold the females’ antennae with their front legs during mating

D Wittmann B Blochtein

1 Laboratório de Pesquisas Biológicas da Universidade de Tübingen, PUC/RS, Av Ipiranga 6681, 90620 Pôrto Alegre, Brazil; 2 Zoologisches Institut, LS Entwicklungsphysiologie, Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany

(Received 12 September 1994; accepted 21 December 1994)

Summary — Epidermal odor glands were found in the front leg basitarsi of males of various subgenera of leafcutter bees from the Old and New World. In these males, the legs, the mandibles and the head capsules are modified. During mating these structures are used by the male to grasp the female and bring the antennae of the female in close contact with the openings of the basitarsal odor glands of the front legs. Odor glands and analogous modifications of associated body structures were also found in xylocopine bees and in a sphecid wasp.

Megachilidae / Xylocopini / Sphecidae / odor gland / mating

INTRODUCTION of orchid bees (Euglossini) are the only example where structurally modified legs serve to collect materials. With dense tufts A conspicuous sexual dimorphism in legs of branched hairs on their front is common in all taxa of bees in which legs (Moure, these males scrape from females have corbiculae or scopae on their 1950), fragrances and transfer them hind legs to transport pollen. In floral oil col- flowers (mainly orchids) lecting bees (Anthophoridae: Centridini, Exo- into pouches of their inflated hind legs malopsini, Tetrapediini; Ctenoplectridae: (Dressler, 1982). The front and/or middle Ctenoplectra Smith 1857; Melittidae: legs of males of some oil-collecting bees, Macropis Klug 1809, Rediviva Friese 1911), namely those of Monoeca Lepeletier 1828 the front and/or middle legs bear scraping and Paratetrapedia Moure 1941 bear combs and oil-collecting structures (Vogel, 1966, and scrapers which closely resemble the 1974; Neff and Simpson, 1981). However, oil-collecting structures of the females. The modified legs are also found in males. Males function of these modifications is unknown. Well known are the adhesive and clasper The purpose of this study was to eluci- organs on the hind legs of Apis drones date the function of some structural modifi- which serve to hold the female during cop- cations in front legs and other body parts ula in flight (Ruttner, 1975; Koeniger and of megachilid bees and to compare them Koeniger, 1991). with similar structures in carpenter bees and The function of the dilated front legs of sphecid wasps. Preliminary reports on our have been elsewhere males of some species of carpenter bees findings published Blochtein and (eg, Xylocopa (Platynopoda) tenuiscapa (Wittmann et al, 1992; Westwood 1840, X (Platynopoda) magnifica Wittmann, 1993). (Cockerell 1929), X (Platynopoda) latipes (Drury 1773), X (Platynopoda) perforator MATERIALS AND METHODS Smith 1861) is only partially understood. For carpenter bees, Anzenberger (1978) and Osten (1989) found the following func- This study was initiated with a survey of modi- tion of the modified legs during copula in fied body parts in males of megachilid bees from the Old and New World. As a flight: males grasp the females in flight and working hypothesis, a general pattern of the function of these struc- place their front or middle legs, which have tures during mating was developed and predic- of over the fringes long setae, compound tions were made on the presence of odor glands eyes of their mate. Very little is known about in the modified legs of megachilid and xylocopine the function of the modified legs in some bees and a sphecid wasp. species of Nomada Scopoli 1770 and in var- The external morphology of preserved males ious genera and subgenera of Megachile of about 150 New and Old World megachilid (eg, Eumegachile Friese 1899, Pseudo- species, 2 xylocopine bee species from India and centron Mitchell 1934, Sayapis Titus 1905, Africa (X (Platynopoda) tenuiscapa, X torrida Westwood 1838 and 3 Melanosarus Mitchell 1934, Acentron (Mesotrichia) species from Brazil (X (Megaxylocopa) frontalis Mitchell 1934) Chalicodoma Lepeletier 1841 (Oliver 1789), X (Dasyxylocopa) bimaculata and Fidelia Friese 1899. Mitchell (1930, Friese 1903, X (Neoxylocopa) nigrocincta Smith 1980), Batra (1978) and Osten (1989) 1854) and 1 European sphecid wasp species assume that the modified front legs in (Crabro cribrarius (Linnaeus, 1758)) was studied Megachile Latreille 1802 play a role during under a stereomicroscope at 40-60x. Dry were in mating. The few ethological observations museum specimens placed boiling water for 10 min to make them flexible during spreading on of bees with modified copula megachilid of the legs and thus facilitate access to the other- front legs (Batra, 1978) indicate that the wise hidden structures. males also cover the eyes of the compound In search of glandular structures, we studied with setae at female fringes of located their the inner morphology of tarsal segments in some front leg tarsi. megachilid bees (M ericetorum Lepeletier 1841, Modifications that resemble those found M willughbiella (Kirby 1802), M rotundata (Fabri- cius 1784), M (Acentrina) anthidioides in and males are also megachilid xylocopine Radoszkowski 1874, M lagopoda (Linnaeus known from As a sphecid wasps. conspicu- 1761), M (Acentron) spp, M (Pseudocentron) ous feature, the front leg tibia of many males spp). Furthermore, we searched for glandular is widely dilated, forming a concave shield. structures in the front legs of X (Platynopoda) During mating, the male places these shields perforator and X (Mesotrichia) torrida, and the C cribrarius Linnaeus. For the scan- over the compound eyes of the female sphecid wasp electron studies et al, 1979; Low and Wcislo, ning microscopic (SEM), speci- (Matthews mens were mounted on aluminium stubs and 1992). Little attention has been paid to the coated with gold and palladium. To study the inte- use of the front leg tarsal segments, the rior surface of the tarsal segments, they were cut mandibles and the head capsule in mating. open, macerated in 5% KOH for 12-24 h, de- hydrated in 70, 80, 90 and 100% acetone, and By doing so, the concave fan of long setae dried at 30°C. covers the compound eyes of the female. To test our hypothesis on the use of modified With his middle legs, he presses the body structures during mating, the behavior in M female’s wings downward and thus prevents was studied at the Botanical Gar- willughbiella her from taking off. The hind legs are posi- den of the of from June to University Tübingen tioned under the female’s abdomen and August 1992 and 1993. We also analysed the A closer look at the copulation behavior of laboratory reared, newly pulled slightly upwards. emerged M rotundata using video recordings. morphology of these body parts gives us a These matings occurred in glass boxes measur- better understanding of their positioning and ing 7 x 2 x 2 cm. function during copulation (fig 1). Males of megachilid species (M (Acentrina) apicipennis Schrottky 1902, M (Pseudocentron) Modified structures of the mandibles terrestris Schrottky 1902) collected in Brazil, and and the head of M the European M willughbiella, captured on flowers capsule willughbiella in Germany, had their heads and front legs removed, washed and extracted in pentane. Gas Below their articulation, the mandibles pro- chromatographic and mass spectroscopic anal- trude into a ’basal’ or ’inferior process’ yses were carried out at the Institute of Organic according to Moure (1943) and Mitchell Chemistry and Biochemistry, University Ham- (1980). These structures have their coun- burg, on a Varian MAT 311. A coupling system in the head using a 50 m x 0.25 mm (id) fused silica column terpart capsule immediately beneath the articulation each mandible. with a FFAP-CB as a stationary phase was of employed. That is, the head capsule is deeply exca- vated and projects ventrally into a pointed protuberance (fig 2). RESULTS Function: When the male has mounted the female, he pushes her antennae into the wide buccal the Although our focus in this paper is on the space by grasping scapi functional morphology of modified body with the mandibular basal processes. By the the male parts, a short description of the positioning widely opening mandibles, of the male during copulation in M willugh- presses the flagellum of each antennae into the excavations of the head In this biella, is also presented. Subsequently, we capsule. one can see the female’s compare it with the positioning of males in M position, flagella out on either side the rotundata. A more detailed description of sticking through gap the mating and territorial behavior in M between the male’s mandibles and the head willughbiella has previously been reported by capsule. Blochtein and Wittmann (1993). Modified structures of the male’s front leg coxa of M willughbiella Case study: overview of the copulation behavior in M willughbiella The coxae of the front legs protrude into long spines which are curved anteriorly. At In M willughbiella, the male mounts the their tip and their margins, these coxal have of female in such a position that his head is spines patches sensory receptors above and in front of the female’s head. He (fig 3). then places his dilated front leg basitarsi Function: When the male has mounted the over the flagella of the female’s antennae female, he places his coxal spines behind and presses them downwards to the fronts. the head capsule of the female. This not only allows the male to tightly hold the head cover a very small number of ommatidia of of the female, but also forces the head the compound eyes of the female. slightly downwards and thus prevents any roll and movements. pitch Modifications of the middle and the hind legs of M willughbiella Modified structures of the front leg tarsus of M willughbiella The tibiae of the middle and the hind leg are slightly inflated and curved ventrally. The basitarsi, and tarsi 2, 3 and 4, bear They bear long setae, but do not form fan- fringes of branched setae which form an like fringes. elongated and slightly concave fan. This fan Function: The males clasp the wings of the has the curvature and almost the size of the females with their middle legs and press female’s compound eye. The anterior-ventral them down and towards her body. With his side of the basitarsus is strongly expanded hind legs, the male clasps the abdomen of and deeply excavated into a ’U’-shaped the female and pulls it upwards. groove (fig 4). This ’marginal excavation’ We should now ask the question as to (Mitchell, 1980) is elongated and reaches the purpose of the clasping structures of the the distal of the second tarsal tip segment. mandibles, the coxal spines and the lateral Furthermore, a hairless black spot is found excavation on the front legs’ basitarsi. on the dilated second and third segment of Clearly, the male stabilizes his position on the tarsus. The surface of these spots the female by grasping her antennae with smooth when viewed with the SEM. appears his mandibles and by pushing the coxal Function: When the male has grasped the spines against her head. By immobilizing female’s antennae between the basal pro- the head and capturing the antennae with cesses of the mandibles and head capsule, the mandibles, the male can readily push he inserts her flagella into the marginal exca- the flagella into the lateral excavation of the vation of the basitarsi and presses them basitarsi. However, holding onto the flag- onto the fronts of the female. Since the flag- ella, the loose ends of the antennae, cannot ella are slightly longer than the marginal provide the male with a firm hold. There- excavation, their tips can be seen extending fore, we hypothesize that the marginal exca- beyond the male’s basitarsi. In this position, vation serves to keep the female’s flagella the concave fans cover the female’s eyes closely attached to the basitarsus of the and serve as blindfolds. The black dots male. If so, this would suggest that chemical

signals are emitted by basitarsal glands. found in M willughbiella can be extended to Indeed such glands were detected. other megachilid bees, and some xylocopine bees and a sphecid wasp, we examined the modifications of the of other bee Odor glands in the front, the middle body parts In our examination of the and the hind legs of M willughbiella species. general, coxal spines, the basal processes at the mandibles and the lateral excavations of SEM analyses of the front legs revealed the the front legs basitarsi has revealed that presence of pores (d = 2 μm) on the sur- most of the with lateral excavations face of the marginal excavation of the species on the basitarsi also have coxal and basitarsi (fig 5a). This is exactly the loca- spines modified mandibles. There are, however, tion in which the female’s antennae come in which the males have either 1 or in contact with the basitarsi. From the inner species 2 modified These surface of the front legs basitarsi, these body parts. body parts are lateral excavation and basal processes pores lead into cuticular ducts (d = 2 μm; of the mandibles without its on I= 120 μm) which end in branched tubules counterpart the head capsule (eg, M (Acentrina) anthid- (fig 5b,c). These tubules are located within or mandibular in combi- the secretory cell. The main compounds ioides), processes nation with coxal but without a lateral found in the basitarsal glands of the front spines, excavation of the front basitarsus legs are carbohydrates and esters. Of all leg (eg, M rotundata, M On mod- species analyzed, 7-pentacosen and pen- ericetorum). many ified front black dots 9 tacosan were the dominating components. legs, (see fig below) are found on the ventral side of tarsal Furthermore, we found pores of odor glands seg- ment 2. In some the black dots are on the tibia of the middle leg and on the species, found on tarsal 2, 3 and/or 4. In basitarsi of the hind legs. On the inner sur- segments rare such as M euzona face of these segments, the pores also lead cases, (Stelodides) into long chitineous ducts (d = 2 μm, I = Perez 1899, males have black dots on the 40-100 μm). The list of compounds, and basitarsus, or as in M (Dactylomegachile) the histology of the basitarsal odor gland sp Mitchell 1934, on the tip of the mush- units, and other epidermal odor glands, will room-shaped spine of the strigillum. In some with be described elsewhere (Blochtein et al, species modified legs (eg, M lagopoda unpublished data). and M (Tylomegachile) orba Schrottky 1913), the black dots are lacking. Function: When the male holds the female’s flagella in the lateral excavation of his front Our examination of the fine structures of and ducts of the odor in the legs basitarsi, the pores of the odor glands pores glands basitarsi has shown that are also are in close contact with the flagella. This pores pre- sent in like M anthid- facilitates close range chemical communi- species (Acentrina) cation during courtship and/or mating. Stud- ioides, M (Acentron) sp, M lagopoda, M and Anthidium mani- ies are in progress on the function of the (Pseudocentron) sp odor glands of the middle and hind legs dur- catum (Linnaeus 1758). We also found odor ing territorial marking and the post-mating glands in M ericetorum, M maritima (Kirby behavioral period. 1802), M (Pseudocentron) curvipes Smith 1853, M rotundata and M willughbiella. In our studies of the front leg tarsal seg- Megachilid bees ments, different patterns of modifications were found within various species of To test whether our explanations of the func- Megachile. We recognize a morphological tional properties of the modified body parts series of modifications of male basitarsal holding structures for the antennae of the 1878, the front leg basitarsus, and the sec- female. This is best illustrated by some ond and third tarsal segments, are folded examples: in such a manner that the 3 segments

- In M ericetorum and M rotundata, the almost form a tube. This tube has a diame- ter in size to that of the males’ front legs do not possess a holding corresponding structure for the female’s antennae. Some female’s antennae. These modifications tarsal segments have elongated setae, but strongly suggest that they also serve to hold the female’s antennae. it they do not form a fan (fig 6). Furthermore, should be noted that males of M (Pseudo- - In M (Acentrina) anthidioides and in M centron) spp have false, hook-like spurs (Pseudocentron) sidalceae Cockerell 1897, which protrude from the anterior surface of the front leg basitarsi are thickened slightly the middle leg tibia. Their shape and position and 2 distinct rows of curved bristles bor- strongly suggest that they serve to press der an elongated area which is covered by the female’s wings downward during mat- a few branched hairs. The width of this area ing. corresponds to the diameter of the female’s antennae. No conspicuous blindfold is pre- sent 7). (fig Case study: overview of the copulation - In M (Tylomegachile) orba, M (Pseudo- behavior in M rotundata centron) framea Schrottky 1913, M (Acent- rina) squalens Haliday 1836, M (Acentrina) brunneriella Cockerell 1917, M willughbiella For our second case study, we selected M and M maritima, the basitarsus is excavated rotundata as a representative of species in which males have no structures for in its long axis. Both sides of the excava- holding the female’s on the front tarsal tion are bordered with bristles, a fan-like flagella leg blindfold is present (fig 8). segments. Males, in this instance, have coxal spines and basal mandibular pro- - In M (Pseudocentron) curvipes, the tarsal cesses. However, odor glands are also pre- 1-4 are dilated and bear a fan- segments sent in their basitarsi. In M rotundata, the like blindfold. The basitarsus is elongated male mounts the female and pushes his This forms a con- laterally. elongated part coxal spines behind the female’s head and lateral excavation and is bordered spicuous with his middle legs he presses the female’s on both sides rows of bristles 4, 9). by (figs wings downward. He then grasps the scapi of the female’s antennae with the basal pro- cesses of his mandibles. The flagella now Exceptions in the pattern protrude on both sides below the head of of modified parts body the male. He then grasps the female’s flag- ella with his front leg tarsi. Subsequently, In M (Chrysosarus) bella Mitchell 1930, M he pins the flagella with his tarsi to the frons (Chrysosarus) melanopyga Costa 1863 and of the female. To fix the flagella in this posi- M (Chrysosarus) inermis Provancher 1888, tion, he hooks the claws of his front legs to the mandible, at its point of articulation, does the inferior margin of the female’s not protrude into a basal process but instead mandibles. While the female is held down has a bundle of stiff bristles which serves and thus motionless, the basitarsi are in to hold the female’s antennae. We also direct contact with the proximal part of the found an exception in the basic pattern of flagella. This clearly shows that even males, the basitarsal holding structures: in males without a holding structure for the female’s of M (Chelostomegachile) otomita Cresson antennae on their front legs basitarsi, can use their modified body parts in such a man- the lower margin of the compound eye, a ner that the openings of their basitarsal odor pyramid-like structure protrudes (fig 12a). glands come in direct contact with the flag- The shield-like blindfold on the front leg how- ella of the female. ever is formed by the tibia (fig 12b). On the ventral side of the strongly dilated basitar- sus, as well as on the other tarsal segments, Modified structures and odor glands we find 2 conspicuous rows of bristles, which in the front legs of xylocopine bees border an elongated area (fig 12b,c). Simi- lar to what occurs in some megachilid and carpenter bees, these structures are suit- In males of some Old World species, for able to hold the female’s instance in X (Platynopoda) tenuiscapa, X flagella. Moreover, we found and ducts of odor (Platynopoda) latipes and X (Platynopoda) pores glands on the inner surface of the basitarsus. perforator, the front legs basitarsi are ’S’- shaped, dilated and bordered by dense hairy fans (fig 10). Although we found spines on DISCUSSION the coxae of the front legs, the clasping structures on the mandibles and the marginal excavations on the basitarsus are The conclusions drawn from our morpho- lacking. In our studies of the inner surface of logical, functional and behavioral studies on the front legs basitarsi in males of X the general positioning of the modified body (Platynopoda) perforator, we found odor parts during copula in megachilid bees are glands in the dorsal parts. The pores, ducts confirmed for other species by a photograph and the end apparati of these glands are of Chalicodoma spissula (Batra, 1978) and similar to those found in megachilid bees an unpublished photograph by F Amiet of (fig 5). In males of some New World xylo- M argentata Friese 1899. Batra (1978) and copine species (eg, X frontalis, X nigrocincta, Sihag (1986) give interesting descriptions X bimaculata), the front leg tarsal segments of the courtship and copulation behavior are not dilated, but bear blindfolds of long and its effect on the female. We are now hairs at their posterior side. On the ante- aware that basitarsal odor glands are rior-ventral margin of the basitarsus of X involved in copulation behavior in various bimaculata, we found an elongated almost megachilid bees, and thus their descriptions hairless area which is bordered by long bris- are subject to a different interpretation. tles suitable for the female’s holding flag- Sihag (1986) studied the mating and cop- ella. More at the basal of importantly, part ulating behavior in 4 Indian megachilid this structure are pores 2 holding (d = μm) species (M nana Bingham 1897, M similar to those found in bees. megachilid cephalotes Smith 1853, M flavipes Spinola Spines, are present on the coxa and the 1838, M lanata Fabricius 1775). We exam- trochanter of the front legs (fig 11). ined his material and found coxal spines and a marginal excavation in M cephalotes, but only coxal spines in M lanata. The other Modified structures of the front legs 2 species had no modified parts. For all and the head in C cribrarius body capsule 4 species Sihag states: "In the dorsal mount- (Sphecoidae) ing position in the beginning, the head of the male projects ahead of the female. The In males of C cribrarius, the mandibles have fore-legs grapple the head of the female. at the upper part of their articulation a hook- The male, then, in this position strikes his shaped process (fig 12a). In contrast, near antennae vigorously on the forehead/anten- nae of the female ... after this the female female’s antennae in close contact to the becomes motionless and her antennae are odor source suggest that at least some of directed downwards." Batra (1978) reports the semiochemicals from the basitarsal on C spissula: "then the male placed the glands are likely to serve as short range sig- wide, flattened, pale, hairy tarsi of his front nals. We are not sure, whether there are legs over the upper part of the female’s com- substances involved which could not be pound eyes and presses her wings down detected by our sampling methods and our with his other legs. If she began to move, GC analysis. Moreover, it is not clear, he rubbed her eyes with these tarsal whether the chemical signals emitted from brushes, which calmed her." The observa- the front leg basitarsal glands are only used tions of both authors further corroborate our for species recognition, or if they also func- findings in regard to the general pattern in tion in mate acceptance. Virgin females of M the positioning of the male’s legs on the rotundata rejected some conspecific males female. Most importantly, in all the cases in mating box tests, but copulated with other so far reported, the male’s front legs made individuals under identical conditions. M contact with the head of the female. It is an willughbiella, under natural conditions, was open question whether the front legs made also observed to reject males. These contact with the antennae. At least in the females literally throw off males by using case of M cephalotes, we assumed that this rapid abdominal jerks. Thus, a female is is the case because the front legs of these clearly able to escape or reject a male. males have a lateral excavation. The elucidation of the overall effects of chemical communication in M willughbiella is further complicated by the fact that males Female choice and chemical have also odor glands on the middle and communication the hind legs, and in sternite 6. Studies on the function of volatiles in territorial mark- and behavior are in At a first glance, the elaborate array of clasp- ing post-mating progress ing structures make it questionable that (Blochtein and Wittmann, 1993). there is any possibility for the female to reject a male, once he has mounted her. Sihag (1986) states: "The female’s rejection Convergent modifications in bees and response only appears in the form of offer- sphecid wasps ing some resistance by not rising and open- ing of her genitalia otherwise she, in a true The similarities in the modifications of front sense, is raped by the male." However, in a legs and functionally related structures in large series of conspecific males of M (Acen- male megachilid and xylocopine bees, and trina) apicipennis, we found pronounced dif- in sphecid wasps, are remarkable. Not only ferences in size of these structures. The do these structures serve the same mechan- holding structures of smaller males would ical functions, but they are also associated hardly fit larger females. Therefore, a with odor glands. Interestingly, in males of female’s choice for a male may also be Xylocopa (Platynopoda) spp, the modified based on his size. Furthermore, the set of front legs serve as blindfolds (Hurd and holding structures and the possible use of Moure, 1963; Osten, 1989) and bear odor chemical communication, or pheromones, glands, whereas in males of X (Mesotrichia) employed by a male during courtship and/or torrida the middle legs bear a blindfold mating, requires finely tuned motor coordi- (Anzenberger, 1978) but no odor glands. In nation. Holding structures for keeping the xylocopine bees, we were unable to detect distinct mandibular holding structures for the front leg basitarsal odor glands to the the antennae of females. Holding structures antennae of females. at the mandibles, however, were found in a sphecid wasp. In contrast to megachilid bees, they are formed by lateral and not ACKNOWLEDGMENTS basal processess of the mandible. When the wasp mandible is opened, it forms a We thank JM Camargo, Padre JS Moure, T Osten clamp with a pyramid-like structure at the and RC Sihag for providing collection specimens, lower margin of the compound eye. In sphe- WS Stephens for sending us pupae of megachilid cid wasps it is the front leg tibia which forms bees, H Schoppmann for patient and skillful assis- tance the SEM F Amiet for a shield-like blindfold. As suggested by during studies, pro- Matthews West Eberhard viding us with his photograph of copulating leaf- et al (1979), cutter bees, W Francke and T for and Low and Wcislo the Taghizadeh (1984) (1992), GC/MS analysis, J Zeil and W Engels for valu- membranous in the blindfold openings may able suggestions on the initial manuscript, and transmit species-specific patterns of light A Dietz who provided helpful criticisms on the signals when held over the female’s eyes. In final manuscript. This study was supported by a this respect, it is noteworthy that the highly DFG grant to DW and a CAPES scholarship to BB. The was carried out as modified front in bees are study cooperative legs megachilid between the of and translucent, and, with the project University Tübingen yellow exception the PUC-University at Pôrto Alegre, Brazil. of a few species, bear black dots. In some megachilid species, without front legs mod- we found disk-like dilations with ifications, Résumé — Pourquoi les mâles de méga- black dots on tarsal 1 to 4. The segments chiles tiennent-ils les antennes des presence of the black dots to be appears femelles avec leurs pattes antérieures of the modification found on independent au cours de l’accouplement ? Jusqu’à the front This could indicate a legs. highly présent on ne sait pas pourquoi les pattes function of these dots. That specialized is, antérieures des mâles de plusieurs espèces these dots serve as visual may species spe- de mégachiles (Megachilidae), de xylocopes cific of illumi- signals by shading (instead (Xylocopinae) et de sphécidés (Sphecidae) of ommatidia of nating) specific groups sont modifiées de façon spectaculaire. En females. In males of many species, these étudiant la morphologie des pattes de ces dots are located at the of rounded margins insectes, nous avons trouvé sur les basi- indentations between the tarsal segments tarses des glandes odorantes. Ces sub- and thus the (fig 9), may augment light-dark stances odorantes sont étalées directement contrast when these front perception legs sur les antennes de la femelle lors de are held over the of the females. eyes l’accouplement. Chez les mâles de méga- chiles il existe d’autres parties du corps qui sont modifiées en rapport avec le transfert CONCLUSIONS de substances odorantes : sous leur arti- culation les mandibules portent une excrois- In conclusion, our studies show that in leaf- sance et les coxas des pattes antérieures cutter bees, carpenter bees and a digger des protubérances pointues. Les tarses des wasp analogous modifications of different pattes antérieures sont élargis et bordés de body parts function as blindfolds and hold- longues soies en forme d’éventail. Chez les ing structures for the female’s antennae. mâles de quelques espèces les basitarses These structures work together to improve sont fortement élargis et creusés d’un sillon the transmission of chemical signals from (fig 4). Les observations faites sur le com- portement d’accouplement de Megachile (Sphecidae) dienen. Bei unseren Untersu- willughbiella et de M rotundata indiquent chungen zur Morphologie dieser Insekten- que les coxas modifiés servent aux mâles à beine, fanden wir in den Basitarsen Duft- s’agripper à la femelle au cours de la parade stoffdrüsen. Wie sich zeigte, werden die et de la copulation. Le mâle attrape avec Duftstoffe dieser Drüsen bei der Kopula ses mandibules les articles basaux de direkt auf die Antennen des Weibchens auf- l’antenne de la femelle. Il essaie ensuite de getragen. Bei den Männchen der Blatt- mettre en étroit contact les basitarses de schneiderbienen stehen weitere modifizierte ses pattes antérieures avec le flagelle des Körperteile in funktionellem Zusammenhang antennes de la femelle. Les mâles de M mit der Duftstoftübertragung: Die Mandibeln willughbiella, par exemple, engagent le fla- sind unterhalb des Gelenkes zu Haken aus- gelle des antennes de la femelle dans le gezogen und die Coxae der Vorderbeine sillon latéral de leurs basitarses. Les tragen lange dornförmige Fortsätze. Die antennes viennent alors en contact direct Vorderbeintarsen sind verbreitert und von avec les ouvertures des glandes odorifé- langen Haaren eingesäumt. Bei Männchen rantes. Lorsque le mâle presse ses pattes einiger Arten sind die Basitarsen stark ver- antérieures sur le front de la femelle, l’éven- breitert und zu einer Rinne ausgekehlt. tail de soies des tarses élargis couvre les Beobachtungen des Paarungsverhaltens yeux composés de la femelle. Les mâles bei Megachile willughbiella und bei M rotun- de M rotundata possèdent bien, sur les basi- data ergaben, daß die modifizierten Coxae tarses de leurs pattes antérieures, des dem Männchen dazu dienen, sich während glandes odoriférantes mais aucune struc- der Balz und der Kopulation auf dem Weib- ture particulière pour maintenir le flagelle chen festzuhalten. Dabei fixiert das Männ- de l’antenne. Lors de l’accouplement ils chen mit den Mandibeln die Basalglieder caressent de leurs tarses les antennes de la der Antennen des Weibchens. Das Männ- femelle et pressent le flagelle avec leurs chen versucht dann seine Vorderbein-Basi- pattes antérieures sur le front, en accro- tarsen in engen Kontakt mit den Antennen- chant leurs griffes sous les mandibules de la geißeln des Weibchens zu bringen. Die femelle. Chez les xylocopes de l’Ancien et Männchen von zB M willughbiella führen du Nouveau Monde et chez les sphécidés dazu die Antennengeißeln in die laterale on trouve des modifications semblables sur Rinne ihrer Basitarsen ein. Dabei kommen des parties du corps, qui servent à appli- die Antennen in direkten Kontakt mit den quer les substances odorantes des pattes Öffnungen der Duftstoffdrüsen. Presst das antérieures directement sur les antennes Männchen seine Vorderbeine auf die Frons de la femelle. des Weibchens, so werden mit dem Haar- saum der verbreiterten Tarsen die Kom- Megachilidae / Xylocopini / Sphecidae / plexaugen des Weibchens abgedeckt. Die glande odoriférante / accouplement Männchen von M rotundata haben in ihren Vorderbein-Basitarsen zwar Duftstoffdrü- sen, aber keine spezielle Struktur zum Fest- Zusammenfassung — Warum Männchen halten der Antennengeißel. Bei der Kopula von Blattschneider-Bienen bei der Paa- streichen sie mit ihren Tarsen über die rung die Antennen der Weibchen mit den Antennen des Weibchens und pressen die Vorderbeinen festhalten. Bisher war Flagella schließlich mit ihren Vorderbeinen unklar, wozu die auffällig modifizierten Vor- auf die Frons, indem sie ihre Klauen unter derbeine der Männchen mehrerer Arten von den Mandibeln des Weibchens einhaken. 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