The Process of Colony Multiplication in the Sumatran Stingless Bee Trigona (Tetragonula) laeviceps

Abstract

Colony multiplication of the Sumatran stingless bee Trigona (Tetragonula) laeviceps was observed from October 1980 to May 1982. Mass flights of several dozen males or of about 1000 workers were observed several times around nests whose workers had started scouting for new nest sites. Transport of building materials to a new daughter nest continued for about 20 days, but the entrance tube was not completed until arrival of a virgin queen. Mass flight of workers and males around the daughter nest continued for about 3 hours. Most workers of the mother participated in this mass flight and were observed to enter the daughter nest, following the virgin queen. After an overnight stay about half of them returned to the mother nest. The proportion of workers remaining in the daughter was about 30 percent when the daughter became virtually independent of the mother (about one week after swarming). Males' mass flight continued around the daughter nest for 2 days after swarming. The young queen was tightly surrounded by workers and made repeated buccal contacts with them for about 5 days after swarming. Oviposition also started one week later. The mother could produce another daughter about one month later. The most remarkable results are return to the mother nest of many workers which went to the daughter nest and the negligibly small amounts of building materials and food carried into the daughter nest, compared with the stocks in the mother nest. These points were compared with other species to clarify characteristics of the reproductive strategy of T. laeviceps. IN TWO GROUPS OF HIGHLY EUSOCIAL BEES, honeybees (Apis) and stingless bees (Meliponinae), colonies are founded by swarming. The process of swarming, however, differs in important aspects between the two groups (Michener 1974, Sakagami 1982). For honeybees a large mass of workers rather abruptly leaves the original with the old queen. By this departure the relation between the original and the swarm is abruptly broken, and a new nest site is selected by scout bees from the bivouac (Lindauer 1955). For stingless bees, on the other hand, the break between mother and daughter colonies is rather gradual, and it is a young queen that leaves the parental nest. Observing several species of the Neotropical stingless bees, Nogueira-Neto (1954) showed the following steps of swarming: exploration by scout workers for a new nest site, gradual shift of workers transporting resources from the mother colony, arrival of a virgin queen at the new site (not always accompanied by a mass of workers), and rupture of the relation of mother and daughter colonies several days to half a year later. Later observations revealed the occurrence of mass emigration of workers with a virgin queen (Terada 1972, 1974; Darchen 1977). Although these and some other studies described the sequence of swarming, few quantitative analyses have been undertaken to answer the following questions: Under what conditions does the mother start swarming? How many workers leave the mother and how much nesting materials, food, or other resources are carried to the daughter nest? These questions are also interesting for testing theories of reproductive strategy (Pianka 1978, Horn 1978, Southwood 1981). But these theories consider only an individual as the unit of reproduction; the optimal reproductive strategy is theoretically derived through individual selection. Therefore, these theories cannot be applied directly to the highly eusocial bees whose unit of reproduction is always a and whose virgin queens lack the ability to found new nests. Wilson (1971) termed this colony in contrast to individual selection. In selection there are three crucial parameters related i Contribution to the ecological and bioeconomical studies of the stingless bees II. 2 Contribution No. 6 of Sumatra Nature Study (Entomology). I Received 21 January 1983, revised 20 June 1983, accepted 26 June 1983. 100 BIOTROPICA 16(2): 100-111 1984 This content downloaded from 207.46.13.21 on Tue, 27 Sep 2016 04:15:00 UTC All use subject to http://about.jstor.org/terms to the reproductive effort of colony: the duration of dependence of the daughter on the mother colony, the proportion of workers which go to the daughter colony, and the proportion of resources that are carried into the daughter nest from the mother nest. If the duration of dependence is short and the two proportions are small, the mother could produce another daughter soon but might reduce the success of the daughter in some degree, and vice versa. The optimal combination of these parameters for each species would be determined, under the species-specific restriction, by environmental characteristics, e.g., resource abundance and enemy pressure. The stingless bees are ideal for comparative studies on these problems because there are about 200 species known from three tropical regions; although principally forest dwellers, some species adapt to savanna and man made environments; and preferred nest sites, population size, and body size vary from species to species, promising a variety of reproductive strategies. Since 1980 we have studied reproductive strategies of several stingless bees in Sumatra, Indonesia. As the first step, this paper aims to clarify the process of multiplication for Trigona (Tetragonula) laeviceps Smith, the commonest species in disturbed areas, characterized by small body size, moderate size, high acceptance of human constructs as nest sites, low aggressiveness, clustered brood cell arrangement, and virtual absence of thermoregulatory ability (Sakagami et al. 1983). STUDY AREAS AND METHODS Two study areas were chosen in the suburbs of Padang: the Horticultural Experiment Station of Sumatera Barat at Lubuk Mintrun (LBMT) and the Laboratory for Sumatra Nature Study at Ulu Gadut (LAB) (cf. Sakagami et al. 1983). At LBMT, T. /aeviceps nests in cavities of tropical fruit trees (rambutan, mango, and durian) or clove, and also in perforated bamboo stems used to support shades for seedlings of the above trees (henceforth S). We set out two types of traps to increase chances of swarming: bamboo stems with a hole, 1.2 cm in diameter (B) and glass topped wooden boxes, covered with wooden lids when they were not examined, with the inside dimensions 7 x 20 x 5 cm (W). At LAB five colonies collected in the suburbs of Padang were transferred to wooden observation hives (0) modified from those of Sakagami (1966). When any rudiments of swarming, particularly mass flights around either established nests or sites available for colonization, were discovered some participating workers were paint-marked and their movements followed to locate the daughter or mother nests, respectively. After arrival of a virgin queen at the daughter nest, extraW152 hu nLM.* tre an baboplaso Ch u,*pl * s2B41