Stingless Bee, Meliponula Bocandei (Spinola)

.��v, .j3io¡. Trop., 11(1 ): 25-45, 1963 Phylogenetic Significan ce of an Unusual African Stingless Bee, Meliponula bocandei (Spinola) by Alvaro Wille* (Received for publication February 7, 1963) The main purpo'Se of this paper is, first, to show that a general knowledge of Meliponula bocandei is essent:al in obtaining a better and greater understanding of the phylogeny of the stingless bees, and second, to indicate the systematic position of this unusual African species. Meliponula bocandei is found throughout most of Africa (Liberia, Ni geria, French Cameroons, Guinea, Congo, Uganda, Angola, Mozambique) where it is highly regarded by the people because of its honey, M. bocandei being the best producer among the African stingless bees. It is said that one nest can yield from 5 to 18 liters of good honey, and the bees are easy to handle. In general appearance M. bocandei looks like a rusty yello".' brown Melipona of almost a centimeter in length. Its tegument is minutely granulo se, w:th the thorax covered with dense and short pilosity. A worker of M. bocandei can be easily differentiat ed from the other species by the very robust hind legs. The femur is stout and swollen; the tibia sub-spatulate, with the lower two-fifths concave, shiny, and slightly bent inwards, while the upper three-fifths is convex, swollen, dull, and finely granulose. The species M. bocandei was qescribed by SPINOLA (12) in 1853 and was regarded for many years as be10nging to the genus Trigona. In 1934, howev er, COCKERELL (1) propased Meliponula as a subgenus of Melipona to include M. bocandei and eight more species. Later, it was found that the additional eight species were not actually very close to M. bocandei. For this rcason, M. bocandel became the only known species of the group Meliponula which was then raised to generic status. The fact that M. bocandei has been included both in the genus Trigona and in Melipona shows already that this species has an unusual set of characters. * Department of Entomology, University of Costa Rica, San José. 25 REVISTA' DE BIOLOGIA TROPICAL 26 MAJOR EVOLUTIONARY TRENDS AMONG THE STINGLESS BEES In order to analyze the position of Meliponula bocandei it is necessary to review the major evolutionary trends among the stingless bees. If we ignore for the moment the species M. bocandei, it is possible to distinguish two majar and diverging lines among the stingless bees. For convenience these two evolu tionary trends can be called the Trigona line and the Melipona lineo That these two lines actually represent monophyletic lines is strongly indicated by the whole constellation of morphological and biological trends and characters .. ' by which these two groups can be separated. For the differences in morphology, reference should be made to TabIe 1, in which the main morphologicaI differences are TABLE 1 Morphological characters differentiating the Trigona line fl'om the Melipona line Characters Trígona line Melipona line Size usually small from 2 to 8 mm Usually rather Iarge (from 8 to in length) and slender 15 mm in length) and róbust Pubeseenee usually short and sparse upper half of head and thorax densely hairy, hairs long Basal area of propodeum usually glabrous, but sometimes tessellate and entirely tessellate and pubeseent pubeseent Length of fore wing usually long and extending well relatively short and not, or beyond apex of abdomen slightly surpassing tip of abdomen Pterostigma realtively broad, and distinetly poorly developed, narrow to rounded or convex below linear, not rounded below Submarginal angle (basal angle of first variable distirtetIy aeute R eell) Hamuli usually from 5 to 8 from 9 to 16 Shape of hind tibia variable normal, without any type of depression Nerve system abdominal ganglion 3 abdominal ganglion 3 loeated in first metasomal located in thorax segement Dorsal vessel thoracÍe portion straight thoracÍe portion making an arch between longitudinal muscles of thorax WILLE: PHYLOGENETIC SIGNI FICANC E OF MELIPONULA BOCANDEr 27 tabulated. In Table 2 the major biological characters are inJicated. When a trend rather than an invariable charaeter is described, the word "usually" is added. TABLE 2 Biological characters differentiating the Trigona line fl'OlII the Melipona fine Characters Trigona line Melipona line Determination of presumably trophicaUy supposedly geneticaUy workers and queens determined determined Size of the virgin qucens larger than workers, with smalIer than workers, especiaUy a notably wider thorax, in width of thorax, and reared ' reared from 'larger royal ceUs from ordinary comb ceUs Ovaries of the newly weU developed underdeveloped emerged queens Rate of production of queens relatively rarely produced frequentIy produced Location of royal ceUs near periphery of combs intermingled in the combs with ceUs of workers and males Nature of the nest entrance usuaUy made out of cerumen usualIy made out of mud and batumen plates Typically, the Mel¡pona line is represented by the genus Melipona and the Trigona line by the genus Trigona. Other recognized genera are merely specíalized branches of the Trigona lineo These two evolutionary trends or lines have been regarded by MOURE (8) as tri bes, namely, the Meliponini and Trigonini. How ever, we should point out that the gap between them is much smaller than that normally found between tribes (e.g., in those recognized by MICHENER (6). The narrowness of this gap is suggested by the difficulty many investigators encoun tered for almost a century in separating Melipona and Trigona. Although it is true that the separation of Melipona and Trigona has been made easier in recent years by the discovery of new and apparently valid taxonomic charaeters, such as those conterned with the dorsal vessel (WILLE, 14) and the ventral nerve cord (WILLE, 16), it is also true that the separation becomes apparently more difficult and uncertain when the characteristics of M. bocandei are considered. For this reason, a careful stlldy of M. bocandei is necessary in order to obtain a better understanding of the general phylogeny of the stingless bees. TRIGONA-LIKE CHARACTERS OF MELIPONULA BOCANDEI Morphologically there are three struetures in Meliponula bocandei which are typically Trigona-like. These structures are: the forewing, the hind tibia, and the ventral nerve cord. 28 REVISTA DE BIOLOGIA TROPICAL FO REWING (Fig. 1): Although the length oE the forewing in M. bocandei is not as great as the most typical Trigona, it is relatively long and extends beyond the apex oE the abdomen. However, the Eeature which gives the Eorewing an unmistakable Trigona-like character is the pterostigma, which, even though smaU, is distinctly rounded below. AIso the submarginal angle is slight1y greater than 90Q• In aH the species of Melipona that are known the sub marginal angle is slightly less than 90Q• HIND TIBIA (Fig. 2): The hind tibia of M. bocandei is definitely not of the Mefipona type, since it is not triangular in shape, and lacks the posterior apical angle. On the contrary, the shape of the hind tibia in M. bocandei is sub spatulate, with the distal posterior comer obliquely truncate and armed with a rasteUum (comb, in MOURE'S terminology, 8) made up of rather weak bristles. Furthermore, the inner side of the tibia has a posterior and slightly depressed bare strip, suggesting that of Plebeia and Scallra. VENTRAL NERVE CORD (Fig. 3) : In M. bocandei abdominal ganglion 3 is locat,ed in the first metasomal segment, as in aH the species of Trigona and unlike Melipona. Moreover, ganglia 6 and 7 in M. bocandei are located in the fifth abdominal segment (fourth metasomal segment); these ganglia are very close, almost fused (Fig. 3, B). It should be pointed out that one of the two males dissected has ganglia 6 and 7 completely fused (Fig. \ C), while, on the other hand, the other male had the same ganglia well separated, with ganglion 7 located in the sixth abdominal segment (Fig. 3, A). These differences in the two males are not very surprising, since it has been shown elsewhere that specimens occasionaHy differ somewhat from the normal types. It is possible, however, that our first male represents the normal type for the males and that the second is an abnormal example. ActuaUy, the second case (Fig. 3 A) is a very primitive condition found previously (WILLE, 16) only in Trigona flllviventris Guérin. In any case, these two mal e examples illustrate the evolutionary trend in M. bocandei toward the fusion of abdominal gangb 6 and 7 as shown in figure 3. BiologicaHy it seems that M. bocandei is similar to Trigona rather than to Melipona. At least, we know from the work of PORTU GAL-ARAÚ]O (9) that the virgin queens of M. bacandei are larger than the workers, and are reared from specialized royal ceUs. MELIPONA-LIKE CHARACTERS OF MELIPONULA BOCANDEI Besides the Trigona characters discussed aboye, MeliPonllla bocandei also possesses certain important features which are typical of Melipona. These are general appearance, body surface, and the dorsal vessel. GENERAL ApPEARANCE: M. bacandei is a very robust bee of about 8 mm in length, with a short and stout abdomen that gives it an unmistakable appear ance of Melipona. It seems appropriate to discuss here the number of hamuli, since, as has be en shown by SCHWARZ (10), the number tends to be correlated with the size oE the bee. Thus, species of small size usuaUy have fewer hamuli, while species of more robust build frequently have a larger number. In M. bo- II7lLLE: PHYLOGENETIC SIGNIFICANCE OF MELlPONULA BOCANDEI 29 candei the average number is nine; this number seems a consequence of the Melipona- like build. The size also explains the specimens of the largest Trigona, like T.

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