Keys for the identification of common bees of Sri Lanka

Illustrated keys are provided for the identification of 41 species of bees in 25 genera and three families that are commonly encountered on flowers of common flowering plants of Sri Lanka. The generic and species keys to bees are annotated with known natural history information on distribution, floral hosts, special behaviour at flowers, nest type and nesting sites. Details of external morphology of bees used in the keys have been included. A brief taxonomic history of bees relevant to Sri Lanka is also included.


INTRODUCTION
There has been a long felt need for a key for the identification of bees of Sri Lanka that are commonly encountered on flowers of a variety of plants including cultivated plants of horticultural and agricultural importance, weeds and the natural vegetation. Previous studies on bees have tended to deal with the four wellknown species of hive -nesting honeybees of the family Apidae. The domesticated Asian honeybee, Apis cerana, the feral giant honeybee, Apis dorsata, the feral dwarf honeybee Apis florea and the stingless bee, Trigona iridipennis are common in rural and urban landscapes. Detailed information on non-honeybees or the solitary pollen bees of Sri Lanka that outnumber the honeybees was lacking until a recent field study 1 on bees by the authors that covered most areas of the country.
This study has documented 138 species of bees in 35 genera collected from areas other than the North and North-East of Sri Lanka 1 . The keys developed in this study aid in the identification of the commonly occurring bees of Sri Lanka.

A brief taxonomic history
The earliest published work on bees of Sri Lanka dates back to the British Colonial Period when Bingham 2 recorded, described and provided keys for 42 species of bees in 15 genera from Sri Lanka. Thereafter, the insect surveys conducted in Sri Lanka  by the Smithsonian Institution, Washington resulted in the identification of several bee species by Sakagami and Ebmer 3 ; Schwarz 4 ; Sakagami 5,6 ; Sakagami; Ebmer & Tadauchi 7 , 8 ; Snelling 9 and Baker 10 . These publications are noteworthy in that they include descriptions and species keys for specific genera. The landmark publication on the bees of the world by Michener 11 has included information and keys for several genera (27) of bees documented from Sri Lanka. An annotated list of bees of Sri Lanka listing 132 bee species in 25 genera and 4 families was published by Wijesekara 12 through a survey of published literature on bees of Sri Lanka.

Features used in the identification of bees
Like all other insects bees have three body regions, head, thorax and abdomen ( Figure 1). A description of the external morphological features used in the keys is given below. Figures given in Michener, McGinley and Danforth 13 have been used for illustration of these features.

Head
The head bears a pair of antennae, two compound eyes, three simple eyes and three pairs of mouth parts formed into a proboscis or "tongue" (Figures 2a & 2b). The difference in the number of antennal segments is useful in sex determination. The apical segments that form the flagellum of the antenna are 10 segmented in the female and 11 segmented in the male. The relative lengths of these segments, especially the basal segments, is of considerable value as a key character. W.A.I.P. Karunaratne     A large number of characters used in the higher classification of bees are based on features of the proboscis. The proboscis is formed of the maxillae and the labium. Each maxilla consists of the cardo, stipes, maxillary palp and galea. The labium consists of the prementum, glossa, paraglossa and the labial palps (Figures 2a & 2b). In structurally more specialized bees, the glossa becomes acute and more or less elongated, the lacinia becomes reduced in size, the number of segments in the maxillary palps is reduced and various other modifications may be found. The proboscis is extended to probe flowers for nectar. Bees are grouped into either short-tongued or long-tongued species based on the modifications in the galea, labial palps and glossa. The labrum (upper lip) and mandibles are relatively simple generalized structures, not markedly different from most insects. However, they show a wide range in form and in relative size in different taxa.
The face is often divided into ill-defined areas, as indicated by dotted lines in Figure 3a. They are the two paraocular areas, the supra clypeal area, the frons or supra antennal area and the vertex. The malar area is between the eye and the mandible. The foveae of the face are depressions, usually black in colour.
The antennae arise from the antennal sockets (alveoli). Nearly all bees have a subantennal suture extending from each antennal socket down to the episternal suture (some have two sub-antennal sutures, below each antenna defining a subantennal area). The epistomal suture defines the upper limits of the clypeus. A longitudinal carina immediately mesal to the antennal base occurs in some bees, which is called the juxtantennal carina ( Figure 3a). In some bees (e.g. Ceylalictus), the paraocular area seems to have moved downwards becoming lobed down into the clypeus on each side. The resultant lobe of the paraocular area into the clypeus is called the paraocular lobe. The term orbit is usually used for the eye margin, inner orbit for the facial margin and outer orbit for the genal margin. The genal area is the region behind the eye and in front of the preoccipital ridge. The ridge surrounding the concave posterior surface of the head above and laterally is called the pre-occipital ridge (Figure 3b). The proboscidial fossa (Figure 3b) is the large, deep groove on the underside of the head into which the proboscis folds.

Thorax
The thorax (Figures 4a & 4b) of bees is a compact structure consisting of three segments; prothorax, mesothorax and the metathorax. The thorax bears legs and wings. The first true abdominal segment is termed the propodeum. The prothorax is represented primarily by the collar-like pronotum. The pronotum extends ventro-laterally forming the pronotal lobe ( Figure 4b). In dorsal view, the mesothorax can be divided into four distinct sclerites; the scutum, scutellum and paired axillae. Laterally, the mesothorax is represented by the mesepisternum. This is sometimes divided by the nearly vertical episternal groove (pre-episternal groove). The episternal groove may extend down, often meeting the anterior end of the horizontal scrobal groove, on to the lower anterior part of the mesepisternum, as in the subfamilies Colletinae and Halictinae. Dorsally, the metathorax consists of the sclerite, metanotum. The metepisternum forms the lateral surface of the metathorax (Figure 4b).
The form and subdivisions of the propodeum are important systematically. The propodeum commonly exhibits 4 distinct surfaces; dorsal, posterior and lateral surfaces. In many species of groups these surfaces are defined by marginal carinae. The dorsal part of the propodeum is called the basal zone (basal area) and is further characterized by striations, reticulations or other sculpturing which are of considerable taxonomic importance. Many bees have a pair of impressed lines on the propodeum (dotted in Figure 4a), beginning near its anterior dorso-lateral parts and extending downward and postero-medially and nearly meeting in or above the propodial pit, a median depression of the lower posterior surface. These lines, together with the anterior dorsal margin of the propodeum, enclose the propodeal triangle.

Wings
The wings of bees exhibit a considerable range of variation between genera and the other higher taxa but are commonly of little help in the separation of species within a genus. Important differences in the forewing include the number of submarginal cells (2 or 3), the relative size of the stigma, the size and form of the marginal cell, the form of the basal vein and 2 nd recurrent vein, and the relations of the recurrent veins to the submarginal cells. Among the veins in the forewing, of special importance are the three veins that look like crossveins: the second abscissa of Rs (or first transverse cubital), first r-m (or second transverse cubital), and second r-m (or third transverse cubital), named according to the Cumstock and Needham system. These veins help to define the sub marginal cells, which are usually either 3 or 2 in number. The veins are termed as 1 st , 2 nd and 3 rd submarginal crossveins (Figure 5a).

Legs
The three pairs of legs bear five segments; coxa, trochanter, femur, tibia and tarsus ( Figure 6). The legs in most female bees differ from those of the other Hymenoptera chiefly in the broadening of the tibiae and basitarsi of the hindleg and to some degree, the basitarsi of the middle legs. Along with the expansion of these parts there has been a development of pollen collecting hairs, which are borne on hind legs in all groups except in the family Megachilidae. Because, male bees carry no pollen, these leg features are lacking, with all segments usually quite slender. In parasitic bees, both sexes are wasp-like in appearance, as the females also have lost their pollen carrying structures.
The tibial spurs are the movable inferior apical spurs on the tibiae; there is only one spur on the front tibia, one on the middle tibia and, in nearly all bees, two on the hind tibia. The inner hind tibial spur is especially important taxonomically. This spur usually has two toothed margins; the inner one that is commonly elaborated in various ways and an outer margin. The spurs are described as pectinate when its inner margin is produced into several long, coarse, often blunt projections, even though the number of such projections is in some cases reduced to only one or two. These spurs provide a hold against their nest burrow walls. Bees pivot on these spurs, somersaulting to change the direction of their head 14,15 . The tibial spines ( Figure 6) are immovable, sharp superior apical projections, usually small in size, often blunt or minute, found in some bees. There are none, 1 or 2, or rarely 3 spines per tibia.
The basitibial plate is on the upper or outer side of the base of the hind tibia of many bees. It is best developed in females and presumably is important for support as bees move up or down with legs bent within their burrows in the   16 . On the inner surface of the hind tibia of most bees is an area of variable size, covered with hairs of uniform length, usually blunt, truncate, or briefly bifid ( Figure 6). These hairs, the keirotrichia, appear to serve for cleaning the wing. In some bees they are replaced by longer, more ordinary hairs that may function as part of the scopa in females. On the hind basitarsus of many female bees is a process that extends beyond the base of the second tarsal segment. Sometimes this process bears on its apex a small brush, the penicillus. Between the tarsal claws there is often a protruding pad-like arolium ( Figure 6).

Scopa
Two forms of pollen collecting organs are found in bees. In all of the pollen bees (except in parasitic bees) they are composed of localized brushes of hairs, and the resulting organ is known as the scopa. Usually these scopal hairs are more elongate and spine-like than the other body hairs, and they may be either simple and unbranched or more or less densely plumose.
The honeybees of the family Apidae have a more specialized structure, called the corbicula or "pollen basket". In such bees the outer surface of the hind tibia is bare and highly polished and is surrounded by a marginal fringe of hairs, forming the basket. Female bees have scopae for holding and transporting pollen while the males lack such structures. Exceptions are the bees of Hylaeniae, Euryglossinae and Colletidae, parasitic and robber bees in various families, and queens of highly eusocial bees (Apidae), all of which lack scopae. The scopa consists of pollen carrying hairs in which pollen is carried back to the nest. In most bees the scopal hairs are on the hind legs, but in non-parasitic Megachilidae they are on the metasomal sterna; in some Collectids and Halictids they are on both the underside of the metasoma and on the hind legs.

Metasoma
Excluding the propodeum, which is the 1 st abdominal segment, the abdomen includes 6 well-defined segments in the female and 7 in the male. Each segment is composed of a dorsal, strongly arched tergum and a relatively flat ventral sternum. There are no pleural plates.
Metasomal terga and sterna are referred to as T1, T2, etc., and S1, S2, etc. T1 and S1 constitute the basal segments of the metasoma (Figure 7a). Each metasomal tergum or sternum consists of a plate commonly marked by some transverse lines. Across the anterior margin, always completely hidden in the intact metasoma, is the antecostal suture. Near the posterior margin of each tergum and sternum is usually another transverse line, the premarginal line, separating the marginal zone from the rest of the sclerite (Figure 7b). T1 differs from other terga because its base is constricted to the narrow connection with the thorax. The terga are always provided with transverse bands of pale hair which are termed as metasomal bands.
The pygidial plate (Figure 7a) is usually a flat plate, commonly surrounded laterally and posteriorly by a carina and in some cases produced as an apical projection, on T6 in females and T7 in males. It is more often absent or rudimentary in males than in females. Soil dwelling females use the pygidial plate to compact the soil of burrows and cells 17 . Dense hairs on T6 of females, on each side of the pygidial plate, constitute the pygidial fimbriae, which are divided into two parts by the plate. T7 of the female is always completely hidden.

Collection of bees
Bees are active when the sun is out and can be collected from flowers, off vegetation and their nesting sites. A standard insect net can be used for collecting bees that is swung rapidly over vegetation. A net with a long-handle is used for collecting bees from tall trees. Bee specimens collected should be curated according to standard methods before identification.

Material used in the key
All materials upon which these keys are based were field collected and the specimens were either identified by experts (Dr. Alain Pauly, Dr. M. Terzo, Dr. S.W.T. Batra and Dr. B.B. Norden) or by the authors using taxonomic keys and descriptions and crosschecked with expert identified reference specimens lodged in the National Museum, Colombo and the Invertebrate Systematics and Diversity Facility (ISDF) of the University of Peradeniya.

Identification keys
The keys have been designed for use with bee specimens mounted on pins viewed under a stereo-microscope (magnification 2 x 0.7 -4.5). Notes on general appearance, distinguished features, habits in life (buzzing at flowers and nectar robbing) and host-plant range as well as their distribution have also been included. This information can be an additional aid to identification. The keys provide salient features of 41 commonly occurring species of bees in 25 genera, and the 3 families (Halictidae, Megachilidae and Apidae).   1. Marginal cell of fore wing tapers much toward its apex, which is not rounded; when there are three submarginal cells, 3 rd is shorter than 1 st and less than twice as long as second submarginal cell (Figure 19).   . Wings fulvous; scopa yellowish white; T1 and T2 thickly covered with reddish-brown hairs; body black; face in front covered with a thick coat of fulvous pubescence; thorax above thickly covered with reddish-brown hairs; T1 and T2 thickly covered with reddishbrown hairs, remainder apically banded with white hairs; wings fulvo-hyaline, fuscescent along apical margin; common below 900 m elevation in all three major zones of the country; largely found on flowers of Fabaceae; solitary bees that nest in bamboo stems and in hollows of stems. -Wings hyaline at base followed by an orange brown tint to end in dark fuscous at the apex; scopa white with the tip black; body black, face in front with fulvous black pubescence; on thorax laterally close to wing base, scutellum above sparsely and propodeum laterally with orange-brown hairs; T1 and T2 with a fascia of dark-brow orange hairs; fascia on T3 narrower and fulvous; T4 and T5 with a narrow white fascia; visits herbaceous flowers, common in all three major climatic zones of the country; nests in hollows of stems.