Lisotrigona Moure, Engel 2022

In a genus-level revision of Lisotrigona Moure, Engel et al. (2022) transferred L. carpenteri to the new genus Ebaiotrigona Engel & Nguyen on convincing morphological evidence. Workers of E. carpenteri are easily distinguished from those of Lisotrigona and Pariotrigona by the yellow face maculation (among other characters, including the slightly larger size of E. carpenteri). This removal from Lisotrigona could also support the behavioural difference between species of the two genera, namely, that E. carpenteri is not truly lachryphagous, or at most only rather weakly or accidentally so. The very similar L. cacciae and L. furva from Thailand are best identified by differences in body size, as shown by Michener (2007), and confirmed with further measurements by Bänziger & Bänziger (2010), viz. head width 1.05‒1.23 mm in L. cacciae and 1.25‒1.41 in L. furva, without overlap. The body length is not a reliable measurement because it is dependent on the crop fullness of the telescoping metasoma. In India, besides the presence of L. cacciae, five new species of Lisotrigona were recently described, viz. L. mohandasi Jobirai & Narendran (Jobiraj & Narendran, 2004), L. chandrai Viraktamath & Sajan Jose, L. revanai Viraktamath & Sajan Jose (Viraktamath & Sajan Jose, 2017), L. darbhaensis Viraktamath, and L. kosumtaraensis Viraktamath & Jagruti (Viraktamath et al., 2023). Whereas in the report by Thangjam et al. (2021) there is no doubt that several specimens of Lisotrigona drank tears in three separate cases in India, according to Viraktamath (pers. comm., 11 March, 2022), the identity of such species remains unknown. Also, there is some controversy regarding the actual number of good species of Lisotrigona in India (Rasmussen et al., 2017; Viraktamath et al., 2021). Regarding Pariotrigona klossi, Schwarz (1939) described it as a variety of P. pendleburyi (Schwarz), then under Trigona, both from Peninsular Malaysia. But Michener (2002 [2001]) found intergrading characters in specimens from Borneo, Sumatra and Malaysia, and proposed P. klossi as a synonym of P. pendleburyi. This was followed by Rasmussen (2008), Rasmussen et al. (2017), and Engel et al. (2018, 2022). However, in lachryphagous specimens found by H.B. in S Thailand, the main characters consistently matched P. klossi, and Michener, whom H.B. had sent specimens for verification, did not question H.B.’s identification. Unfortunately, Michener died before we could redescribe P. klossi for validation. This is now in preparation, based on additional material. Marking Experiments and Feeding Behaviour of the Bees This was carried out in N Thailand, with wild populations of Lisotrigona in forest sites to make sure that the behaviour was not potentially influenced by artificial components (e.g., bees from meliponaries, degraded environment). Two sites were visited at least once monthly, May 2013 to November 2014, another was visited daily, 31 May to 20 June, 2013; session time lasted 1.5–11 h depending on the bees’ harvesting time (averaging more than 3 h), total session time 360 h (B ӓ nziger, 2018). Bees were marked (Fig. 3) while they avidly sucked tears, H.B. being both lachrymation source and experimenter, by his applying a minuscule drop of waterproof paint to the mesosoma back with a finely trimmed brush, viewed in a concave mirror. Generally, during one day, only one or two bees were marked, the touching causing the bee to fly off. If she returned, the colour, shape and position of the mark, which differed in every bee, were photographically recorded for correct recognition among large assemblages over hours, and days. The marking, 34 L. cacciae and 23 L. furva, revealed that the very same bees can visit human eyes up to 78 and 144 times in one day, respectively. Depending on the bees’ position at the eye and competition with other bees, sucking lasted 0.4‒6.2 min (average 2.2 min) in L. cacciae, 0.4‒5.3 min (average 1.6 min) in L. furva. Intervals between consecutive visits were 1.5‒7.5 min (average 3.3 min) and 2.0‒8.0 min (average 3.8 min), respectively. In one day, the same bees may collect tears for up to 10.5 h (includes round trip time), average 3 h 15 min in L. cacciae, 2 h 14 min in L. furva; five workers of each returned on the following day for up to 78 and 44 harvesting bouts, respectively; one L. furva came on three consecutive and on the seventh day. Tear drinking occurred throughout the year (rainy, dry hot, and dry cold seasons), except during heavy rain and at temperatures below 22°C when no workers left the colony to forage. Lachryphagy was observed even during light rain and after a downpour. So water was not the principal component sought. The other well-known component is salt (NaCl) but, generally not appreciated, there is a third main component, viz. proteins, and they are on a par with that of salt, ca. 6.7 mg in 1 ml (Rauen, 1964), 200 times the proteins present in sweat. Tear collecting is not a simple matter of imbibing moisture; it requires special behavioural adaptations because the source is not dead matter or a flower, but can be a highly mobile, sensitive and reactive vertebrate. Although single experienced tear collectors can be so surreptitious and gentle to occasionally avoid detection by the host, more often they tend to be avid and persistent to become pestiferous when in large groups. The most critical time for lachryphagy is during the bees’ approach to the eyes – not while sucking there. Humans normally flip them away when circling near the face (in zig-zag flight in the horizontal plane, whereas the common lachryphagous drosophilid flies tend to zig-zag vertically). The bees are likely to return and, if they manage to avoid the flipping and are about to reach the eye, the eyelids may automatically blink repulsing the bee. Animals, especially large herbivores, are less sensitive but flip with their ears, chase them off by tail, paw, claws, or shake their head. But in their persistence the bees tend to return time and again – like face flies do. The host may walk away but, unless running, the bees tend to follow in pursuit. The most experienced tear collectors will fly in low and very gently land below near the cilia or at the inner corner of the eye (e.g., Fig. 3) (no eyelashes there), less often at the outer corner, and then advance to where their proboscis can reach the tears accumulating in the menisci and trench between lid and eyeball. They evidently crawl by using only the tarsal soft arolia pads but with the claws automatically in retracted position, as described for honey bees when crawling on vertical smooth surfaces (Federle et al., 2001). Once landed and feeding at the eye, often only a faint tickling is perceived, if at all (H.B. occasionally had to check by mirror if a bee was still sipping or had already departed). The bees’ proboscis is very fine and soft (about 1mm long, a third of the bee’s body length, and only 0.025 mm wide distally) so essentially it is not perceived on the conjunctiva and the eyeball, unlike the bees’ tarsi and claws of inexperienced drinkers which may cause tickling to the host. When settled, the bees would not fly off if the host walks or even slowly runs away, but continue to feed until satiated. Analysis of 117 photographs of Lisotrigona at human eyes revealed that none of the 302 bees present carried pollen loads, whether small or large (Fig. 4), in their corbiculae. From stereomicroscope checks of collection specimens from eyes, only a few had pollen remnants, presumed result of the age polyethism from previous pollen collecting, or from contacts with nest-inmates. Because, as detailed above, lachryphagy is not a simple imbibing of liquids, but requires specific and unusual behavioural adaptations, including additional features described below (e.g., the consecutive bouts of tear drinking instead of switching to the much easier sucking of sweat), B ӓ nziger (2018) proposed that Lisotrigona might have specialized tear collectors – a new division of labour in meliponines sensu Michener (1974), who used it in a broad sense, which in Lisotrigona probably is a part-time division of labour. Bee Scent Marking and Recruiting Some Lisotrigona were also seen along the groove between the lids of closed eyes of a drowsy or sleeping animal host, e.g., a dog. Presumably the bees can locate the eye when they have scent marked it during a previous visit, or when attracted by the odour of tear incrustations or tear seepings along where the lids meet. Scent marking is indeed likely to occur: a fully satiated bee with turgid crop would not directly fly away but often remain a second or so while moving her head, antennae and forelegs, and then causing a typical tickling sensation to the lid/cilia of H.B. as if forcibly grasping them for an instant on take-off. Such head movements have been noted in neotropical Trigona hyalinata (Lepeletier) for odour-marking by mandibular glands (Nieh et al., 2003), and in Melipona seminigra Friese for tarsal ‘footprint’ marking (Hrncir et al., 2004). Quite often H.B. felt a slight burning or itching sensation at the eyelid, continuing after the bee had left, which indicate probable cases of scent marking. The observation that there tended to be an exponential increase in arrivals following the first tear collector, indicates that Lisotrigona employ some form of recruiting. No traillaying was observed. Possibly, an experienced collector piloted a recruit by sight and/ or by an aerial scent plume released by the guide. Occasionally, H.B. noted that when a Lisotrigona was squeezed between his fingers, a strong odour was perceived; such a volatile might be used as a guiding plume. This type of recruiting had been proposed by Lindauer & Kerr (1958) for neotropical meliponines. The information exchange and recruiting behavior in Lisotrigona supports the use of the term ‘congregating’ rather than ‘aggregating’ when describing lachryphagous Lisotrigona. The former su