Rediscovery of Tetragonula praeterita after 1860: an unremarked common stingless bee endemic to Sri Lanka

Three species of stingless bees are documented from Sri Lanka, namely, Tetragonula iridipennis (Smith), Lisotrigona cacciae (Nurse) and the endemic Tetragonula praeterita (Walker). Tetragonula irdipennis is the well-known, widely distributed stingless bee in Sri Lanka while L. cacciae is a recent record of a tear drinking stingless bee from a single site in Sri Lanka. Until the recent rediscovery, T. praeterita was known only from its type specimen deposited in the British Natural History Museum, London with Sri Lanka as its locality and 1860 as its date of description. Location of several stingless bee nests, with an entrance different to that of the well-known T. iridipennis, led to the re-discovery of T. praeterita. Its nesting sites, characteristics of the nest entrance tube and the morphological and morphometric differences of the worker caste compared to those of T. iridipennis are presented in the paper. Eight species of stingless bees have been reported from the Indian subcontinent. It is possible that more than three species of stingless bees occur in Sri Lanka.


INTRODUCTION
Stingless bees (Hymenoptera: Apidae) of the tribe Meliponini are known to have existed in the tropics for well over 65 million years, much longer than the stinging Apis bees (Camargo & Pedro, 1992; and southern subtropical areas of the world. They are considered as major pollinators in the tropics (Michener, 1974) and are particularly common in tropical America and Southeast Asia. According to Rasmussen (2013) there are eight species of stingless bees in the Indian subcontinent. from Sri Lanka was Tetragonula iridipennis (Smith, 1854). The type specimen of this species (deposited in the British Museum of Natural History, London) is from ca. 467 m a.s.l.), according to Rasmussen (2013). Until the recent discovery of a new tear drinking stingless bee from Sri Lanka by Karunaratne et al. (2017), stingless bees of Sri Lanka was known only by the single species, Trigona iridipennis, known as Tetragonula iridipennis since 1961. Moure (1961) addressed the change in the generic name from Trigona to Tetragonula in his wide distribution in the island and is known to nest in a variety of wooden structures. In 2017, Karunaratne et al. reported a new stingless bee species Lisotrigona cacciae (Nurse, 1907), from the Knuckles Forest Reserve of bee to be reported from Sri Lanka. Rasmussen (2013) in his publication on the eight species of stingless bees of the Indian subcontinent, records yet another stingless bee species, Tetragonula praeterita (Walker, 1860) from Sri Lanka, known only from a single specimen deposited in the British Natural History Museum, and described by Francis Walker in 1860. The stingless bees build elaborate hives often characteristic to a species or to a higher taxon (Michener, 1974;Sakagami, 1982). The individual species are recognised from their nest entrances and often their nest site (Roubik, 2006). A recent survey conducted to record the distribution of nests of stingless bees within the Kandy District revealed the presence of nests with an external nest entrance tube different

March 2018
Journal of the National Science Foundation of Sri Lanka 46 (1) from that of typical T. iridipennis. This observation led to further investigations and descriptions; including the distribution of this new nest type in the Kandy District, the morphology and morphometric data analysis for T. iridipennis.

METHODOLOGY
Field surveys were conducted in several locations within in 2016 to record the nests of stingless bees, making detailed observations of the type of external nest tube/ entrances. The nest entrances were photographed and the entrance tube/types, 55 individuals from each nest type The key of Rasmussen (2013) was used for the features of nests, specially the nest entrance tube, were taken using a camera. Selected morphometric measurements of the head, based on information given in Sakagami et al. (1996), such as the inner ocellar distance, upper inter ocellar distance, head width, inter-antennal distance and eye length were made using a micro view USB digital microscope (×650). The morphometric data were subjected to statistical analysis, sample t-test and principal component analysis (PCA) to determine the extent of variation among individuals from different nests.

RESULTS AND DISCUSSION
Out of 65 stingless bee nests located, 31 stingless were recorded from the study area. All the individuals

Diagnosis
Worker female: The two species of Sri Lanka Tetragonula; T. iridipennis and T. praeterita are similar in appearance, the latter species is slightly smaller than the former. The major difference in the worker bee lies in the arrangement of hairs on frons and clypeus of the two species: plumose hairs on clypeus and frons are abundant in T. iridipennis and they are sparse in T. praeterita (Rasmussen, 2013).

Comparison of morphometric data of the head of T. iridipennis and T. praeterita
Analysis of morphometric data of the variation in head measurements of the worker bees of the two species all measured variables (Table 1). This observation was are seen (Figure 1). The highest contribution to the variation is from the head-width (covariance = -0.652).

External nest entrance tube:
In nests of T. iridipennis, the nest entrance is sticky (Figures 2a and 2b) due to resin and is circular-oval with a length of 23 ± 9.0 mm (widest part measured) and a width of 17 ± 6.7 mm (n = 7) (Figure 3). The nests are found mostly in tree trunks and crevices of cement ( Figure 2a) and rock walls (Figure 2b). In contrast, the nests of T. praeterita have length of 17.4 ± 4.0 mm and a width of 6.0 ± 0.7 mm (n = 5). Its nests are found in wooden man-made structures such as electricity meter frames (Figures 3a1 and 3a2), window frames (Figure 3b1), crevices of cement and rock walls ( Figure 3b2) and abandoned tires (Figure 3c). The nest tubes were formed of wooden particles, sand particles or both glued together with resin. The nests of the two species are common in houses and buildings within the Peradeniya University premises in the Kandy District.

Behaviour of guarding worker bees at the nest entrance:
In T. iridipennis, worker bees that guard the nest entrance did not change their behaviour when an object was moved closer to the nest. In contrast, in T. praeterita,  Couvillon et al. (2008), the larger nest entrance constructed by T. iridipennis the entrance tube guarded by more aggressive workers, compared to T. praeterita. The temporary sealing of the nest entrance tube at night by T. praeterita may reduce predator and robber pressure (Roubik, 2006). In contrast, sticky nest entrance of T. iridipennis may 2006). Nogueira-Neto (1997) showed that stingless bees actively immobilised any intruder to the nest using resin deposited in the nest. Although stingless bees the nests of stingless bees, particularly of T. praeterita are vulnerable to destruction by humans as they also use man-made structures for nesting. The recent survey revealed that more than 90 % of the nests are built on the wooden frames of electricity meters. According to personal information obtained from meter readers, house not knowing that the nests belong to stingless bees. Therefore, public awareness on the importance of these bees that are harmless is timely for their conservation. The re-discovery of T. praeterita many decades after of the country.