Bembix antoni Krombein & van der Vecht 1987

Bembix antoni

ETYMOLOGY.—The taxon is named for the late Anton Handlirsch, whose monograph of the world fauna of Bembix (1893) set a high standard for systematic work on the genus.

This is one of the two largest Ceylonese Bembix, females being 19–20 mm long, and males 17–20 mm. Bembix lunata Fabricius may attain this size but it is readily distinguished from antoni by the red rather than black ground color of the body. Both sexes of these species differ from their Ceylonese congeners in having more robust mandibles with an oblique cutting edge beyond tooth (Figure 11).

Bembix antoni occurs in both Sri Lanka and South India, apparently in forested areas. Within Sri Lanka it occurs more commonly in the Wet Zone where the average annual rainfall is some 3900 mm. However, single individuals have been collected at Mau Aru, Dambulla, and Padaviya in the Dry Zone where the average annual rainfall may be no more than 1100 mm. Its closest relative, budha Handlirsch is widely distributed in eastern India but has not been collected in Sri Lanka. The two species are not known to occur together in South India where antoni has been collected only in the Walayar Forest in south Malabar near the west coast and budha only in Karikal, Thanjavur (= Tanjore) near the east coast.

This species belongs to the small papua Group of Handlirsch. He placed in that group his papua, budha, pinguis, and pugillatrix together with melancholica Smith. An additional distinguishing character of this species group not noted heretofore is the series of strong transverse carinae across the middle of the venter of the paramere (cf. Figures 7, 9) some of which become lamellate in certain species. These parameral carinae occur in males of papua, budha, antoni, and pugillatrix but not in melancholica; we have not seen males of pinguis. Such parameral carinae were not found in any of the North American or Australian species studied by Evans and Matthews (1968, 1973) and may be unique to the papua group. The parameral flange is relatively small and directed laterad.

The male genitalia of antoni and budha (Figures 7–10) are strikingly different, particularly the parameres. Those of antoni are broader, have denser, longer setae and more numerous, stronger transverse carinae across the middle. The external differences between these two species other than color are few and subtle. Both sexes of antoni have the clypeus slightly convex medially beneath the basal keel whereas this median area is slightly flattened in budha. A more noticeable distinction is the outline of male abdominal tergum 7, which is definitely lobate at the apex in antoni (Figure 19), whereas in budha (Figure 20) the sides are only slightly concave before the rounded apex.

Minor but reasonably reliable color differences separate the two species. Females of antoni have a pair of large, basal, black spots on the clypeus that sometimes coalesce, the transverse yellow band on tergum 1 is divided in the middle and tergum 6 is entirely black, whereas females of budha have the clypeus yellow, at most with a pair of tiny black spots, a broad uninterrupted band on tergum 1 and a large yellow spot sometimes covering almost the entire exposed part of tergum 6. Males of antoni have black clypeal spots though smaller than in the female and tergum 7 is usually black, only occasionally with a pair of tiny yellow spots, but those of budha have a yellow clypeus and tergum 7 has a large yellow area. Males of both species have a broad, uninterrupted, yellow band on tergum 1, but the bands on this and succeeding terga are narrower in antoni.

MALE (all figures from paratypes).—Length 20 mm, forewing 13 mm, wing index 1.87. Mandible (Figure 28b) stout, curved toward apex, inner margin with large oblique cutting edge beyond tooth, index 1.8; clypeus 1.76 times as wide as high, slightly convex medially below basal keel; least interocular distance about a third of distance between antennal sockets and anterior ocellus, 0.49 times eye height; center of vertex slightly below top of eyes; scape 2.3 times as long as wide; first flagellar segment 3 times as long as wide; flagellar segments 6–8 widened, tuberculate in profile, 11 concave in profile (Figure 22); flagellar segments 4–11 modified ventrally, with sensory concavities increasing in size toward 10, that on 11 small and on basal third (Figure 21); forefemur rounded beneath, × 3.0 as long as wide; forebasitarsus 3.8 times as long as wide, bearing 6 pecten spines; midfemur weakly serrate beneath, not sharply edged; tergum 7 lobate at apex (Figure 19); sternum 2 (Figure 17) moderately punctate, median process low, rather thin, apex in profile forming a blunt tooth; median process of sternum 6 low, obtuse in profile, continuing to apex as a low ridge (Figure 18); sternum 7 (Figure 15); genitalia (Figures 7, 8).

Color: black, the following yellow: mandible except apical third, labrum, clypeus except pair of oblique basal spots, scape beneath and a narrow line laterally, front except small oblique spot from clypeus to lateral margin of antennal socket and broad U-shaped mark surrounding anterior ocellus and extending halfway to antennal insertions, band along posterior orbit narrowing above, pronotum except transverse anterior blotch, scutum with median U-shaped mark and lateral band, broad curved band across middle of scutellum, metanotum except narrowly at apex, mesopleuron except blotch adjacent to pronotal lobe, most of metapleuron, most of propodeum except narrow line adjacent to metanotum, broad V-shaped mark on posterior surface and vertical bar on middle of lateral surface, forecoxa beneath, mid- and hind coxae laterally, trochanters apically, all femora except stripes above and spots at apices beneath of mid and hind, tibiae except short lines or spots beneath, tarsi except apices beneath of fore and of apical segments of mid and hind, broad band across anterior two-thirds of disk of tergum 1, tergum 2 except pair of narrow transverse subbasal spots and narrow band angularly widened in middle on posterior fourth, tergum 3 similarly marked but spots wider, terga 4–6 with basal black areas not enclosed, posterior black band on apical third angularly produced anteriorly in middle; tergum 7 with small lateral spot posteriorly adjacent to lobate apex; posterolateral spot on sterna 2–6 decreasing in size posteriorly. Wings hyaline; vestiture pale, short, and suberect on clypeus, long, denser and erect on front, vertex, gena, shorter, dense and erect on thorax, brown on dorsum, pale on sides, terga with quite short, moderately dense, suberect brown setae on terga, sparser setae on sterna.

FEMALE.—Length 19 mm, forewing 12.5 mm, wing index 1.86. Mandible (Figure 28a) stout, curved toward apex, inner margin with large oblique cutting edge beyond tooth, index 1.8; clypeus 1.88 times as wide as high, slightly convex medially below basal keel; least interocular distance 0.53 times eye height; vertex slightly below top of eyes; scape 2.8 times as long as wide; first flagellar segment 3.5 times as long as wide; forebasitarsus 2.8 times as long as wide, with 6 pecten spines; scutum with small subcontiguous punctures; sternum 2 with moderately large, scattered punctures medially, punctures laterally smaller and separated by less than the diameter of a puncture; tergum 6 narrowly rounded apically, laterally with dense small punctures, a narrow median strip smooth medially except for a few larger scattered punctures.

Color: black, the following yellow: mandible except apical third, labrum with a median decolorized strip, clypeus with a pair of large basal spots narrowly joined above, stripe on venter of scape, front except small oblique spot from clypeus to lateral margin of antennal socket and broad U-shaped mark surrounding anterior ocellus and extending halfway to antennal insertions, stripe on outer orbit narrowing above, pronotum except transverse mark anteriorly and small blotch on lobe, scutum with median U-shaped mark and lateral stripe, median band on scutellum broadened at side, metanotum except narrowly at apex, mesopleuron except blotch below pronotal lobe, most of metapleuron, most of propodeum except broad V-shaped mark on posterior surface with a median extension dorsad and vertical strip on lateral surface, coxae and trochanters black and yellow, rest of legs yellow except stripes posteriorly or ventrally on femora, beneath on tibiae, stripe beneath on forebasitarsus and at apices of next three segments, tergum 1 with a median stripe narrowly interrupted on midline, tergum 2 black anteriorly and with a broad stripe across middle posteriorly enclosing two transverse oval spots, terga 3–5 with a transverse band across middle, deeply biemarginate anteriorly and with a median emargination posteriorly, sterna 2–4 with rounded posterolateral spot decreasing in size posteriorly. Wings and vestiture as in male.

VARIATION.—Males are 17–20 mm long. The process on sternum 2 is sometimes evanescent in Sri Lankan specimens but better developed in South Indian specimens, and the process on sternum 6 is rarely weaker. Most males are maculated like the holotype; the clypeus is rarely entirely yellow and spots on tergum 7 are lacking in most. The male from Ambame Hena and one from South India are notably less maculated; the U-shaped mark on the scutum is reduced to three lateral and apical spots or to a pair of tiny spots anteriorly near middle, and the lateral band is narrower or separated into two spots; and tergum 1 has separated narrower spots and bands on terga 2–6 are noticeably narrower.

Females are 19–20 mm long. They are very similar to the allotype in structure but there is slight variation in coloration. Specimens from Padaviya and South India have more reduced markings. The darkened, decolorized streak on the labrum is occasionally lacking, the clypeal spots may be broadly joined, the U-shaped mark on the scutum may be divided into lateral and posterior spots or represented just by a pair of short, narrow, anterior spots, and the spots on the sterna may be smaller, that on 4 lacking or one present on 5 also.

COCOON.—The cocoon is ovoid with a more tapered posterior end, 25 × 10 mm, with firm walls of sand grains spun together with silk. It has six elevated single pores scattered around the circumference about 12 mm from the anterior end.

TYPE MATERIAL (USNM except as noted in parentheses).—Holotype : Sri Lanka, SABARAGAMUWA PROVINCE, Induruwa Jungle, Gilimale, 13–15 Mar 1979, K.V. Krombein.

Allotype : Same label data but 8 Mar 1979.

Paratypes: 20, 4, same label data but 7–8 and 13–15 Mar 1979 (1 in Malaise trap); 1, same locality but 16–19 Apr 1981, K.V. Krombein, L. Weeratunge, P. Leanage; 1, 4, Ratmalana District, Ambame Hena, 8 mi W Kalawana, 27 Mar () and 4 Apr 1981 (3), and reared ca 12 Feb 1982 from cocoon collected 4 Apr 1981, K.V. Krombein, P.B. Karunaratne; 1, SOUTHERN PROVINCE, Galle District, Sinharaja Jungle, Kanneliya section, 13–16 Jul 1978 (in Malaise trap), K.V. Krombein, P.B. Karunaratne, T. Wijesinhe, V. Kulasekera, L. Jayawickrama; 1, NORTH CENTRAL PROVINCE, Anuradhapura District, Padaviya, 180 ft, 2–8 Nov 1970, O.S. Flint, Jr.; 1, CENTRAL PROVINCE, Matale District, Dambulla, 21 Feb 1953, F. Keiser (Basel); 1, WESTERN PROVINCE, Colombo District, Labugama, 12 Aug 1975, P.B. Karunaratne (Colombo); 1, India, S(outh) Malabar, Sep 1946, P.S. Nathan; 2, 2, S(outh) India, S(outh) Malabar, Walayar Forests, 1000 ft, 8 Sep 1947 (), Apr 1951 (), Sep 1952 () and Sep 1956 (), P.S. Nathan (latter pair in Corvallis). A pair of USNM paratypes will be deposited in the National Museum, Colombo, two males and one female in the Rijksmuseum van Natuurlijke Historie, Leiden, a pair in the British Museum (Natural History) and a male in the Oxford University Museum.

Three specimens of antoni from the Colombo Museum are excluded from the type series because of their poor condition. Label data are: 1, (Southern Province, Matara District) Dondra, Sep 1911; 1, # 23; 1, Ellahara, Oct 1909, O.S. Wickwar (this locality not listed in available gazetteer.)

Bembix antoni

This large species was found nesting only in or near lowland rain forest in Ratnapura District in the southwestern part of Sri Lanka where the average annual rainfall is some 3900 mm. One male was collected in a Malaise trap in the Kanneliya section of the Sinharaja Jungle, Galle District, another locality in the lowland rain forest. However, other collectors have captured the species at localities in the Dry Zone where the average rainfall is as low as 1500 mm annually.

HABITAT.—The first nesting site was in the Induruwa Jungle, Gilimale, where antoni nested in level, coarse, riverine sand along the banks of a rocky stream. There were many boulders in the stream bed and on the banks, and rather heavy vegetated cover of grasses, herbaceous plants, and shrubs on the banks. The area was shaded by taller trees during much of the day. The soil below the surface was a damp sandy loam underlaid by a hard clay stratum. A second nesting site was found at a small, wayside, Hindu shrine, Ambame Hena, 13 km W of Kalawana. Adjacent to the shrine is a rectangular courtyard of some 50 m2 with a flat surface of coarse, firmly compacted, riverine sand brought up from the Kukulu Ganga, flowing some 20 m below. Viable cocoons of the wasp may have been brought up with the fill, or perhaps females nesting on the banks below may have found this area when they searched for prey. The surface of the compacted sand was swept every morning, so most nests did not have a spoil heap of excavated soil. The sand was very moist beneath the surface and overlaid a stratum of stone rubble at a depth of 15–19 cm that limited the depth of the nests.

ADULT ACTIVITY.—Three females were nesting at Gilimale 7–8 March 1979. There was also an aggregation of 15–20 males flying swiftly and erratically low over this site of about 100 m2 on these dates but none attempted to mate with a nesting female; perhaps they were awaiting the emergence of virgin females. Two more females were collected in a Malaise trap nearby on 13–14 March, males were again flying over the nesting area but no females were nesting. The colony was not active when we revisited Gilimale several times during March and April 1981.

Karunaratne saw several males flying over the nesting site at Ambame Hena on 27 March 1981, and also noted a pair flying in copula. Six females were nesting when we revisited the site on 4 April. We saw only one male that hovered close above a digging female but it did not attempt to mate.

NEST CONSTRUCTION.—We did not observe initiation of a nest. Two incompleted nests at Ambame Hena had burrows penetrating at 20°–30° for 13–14 cm where they ended blindly at the layer of rubble. Both wasps were inside when we dug these nests and had sealed the entrances from within. One nest at Gilimale went downward at 30° for 25.8 cm, ended at the stratum of hard clay at a depth of 34.7 cm, and there was no cell. The wasp was not in that nest when we dug it up but was captured later.

A wasp at Ambame Hena emerged from a sealed burrow at 1000. She had begun this nest that morning for there was a large spoil heap of excavated soil behind the entrance about 6 cm long, 4 cm wide at the middle and 2 cm high. (Other nests did not have such spoil heaps because the sandy area was swept quite early every morning.) She continued to excavate sand, pushing it backward, but sometimes emerging head first. At 1007 she sealed the entrance, using loose sand from the spoil heap, and then flew off. She returned without prey in 5 minutes, scratched open the entrance and leveled some of the spoil heap. She then excavated a little more sand, made a temporary closure and leveled more of the spoil heap. She flew off at 1020, leaving a spoil heap that was now 15 × 10 cm maximum length and width and 1 cm high in the middle. The nest had now been completed for she returned with a first prey at 1045.

NEST STRUCTURE.—The single completed nest at Gilimale had a burrow diameter of 10 mm, went downward at an angle of 30° for 39 cm, and ended at the stratum of hard clay. The cell dimensions could not be ascertained because of the occurrence of fine roots adjacent to the cell, but we recovered a small wasp larva, a whole prey, and head of a second prey.

Four nests at Ambame Hena had a burrow diameter of 7–11 mm. The burrows went downward at shallow angles of 30°–35° for 16.9–24.8 cm and turned horizontally for 3.8–9.1 cm when each met the stratum of hard rubble at depths of 15–19 cm. The ellipsoid cells were 2.4–3.5 cm long and 2.0–2.5 cm wide and high at the middle.

NEST PROVISIONING AND PREY.—The single provisioned nest at Gilimale contained a very small wasp larva, a whole calliphorid, Chrysomya megacephala (Fabricius), 8 mm long, and the head of a large syrphid, Eristalinus arvorum (Fabricius). There were no wings in the cell so the female may have removed them before bringing in the second prey.

At Ambame Hena one female brought prey at 0951 to a burrow that had a temporary closure. She left the burrow at 0954 but did not make a closure. She returned without prey at 1004, flew away at once without entering the nest, and returned with prey at 1005. She left at 1008, again without making a closure. At 1013 she returned with a prey, took it into the nest, and sealed the burrow entrance from within in a few seconds. The burrow was still sealed at 1025 and again at 1130 when we excavated the nest. The upper 12 cm of the burrow was solidly plugged. One may speculate from this that the wasp had brought in a sufficiency of food for the rest of that day. The wasp was in the cell 15 cm beneath the surface together with a small larva, four fresh female calliphorids, Calliphora megacephala (Fabricius), 8.5–9 mm long, and the remains of a fifth. Females usually made a temporary closure at the burrow entrance before departing upon a provisioning flight. However, one of the Gilimale females flew with prey to a nest whose entrance was open.

Two other nests at Ambame Hena contained fresh whole flies and some fragmented prey identified as follows: