Schwarziana quadripunctata

Schwarziana quadripunctata is a small, stingless bee found in a stretch of the South American Amazon from Goiás, Brazil, through Paraguay, to Misiones, Argentina. This highly eusocial insect constructs earthen nests in the subterranean level of the subtropical environment, an unusual feature among other stingless bees. The species ranges in sizes from 6.0 to 7.5 millimeters and feeds on a diverse diet of flowering plants found abundantly on the forest floor, including guacatonga (Casearia sylvestris) and the mistletoe species Struthanthus concinnus. S. quadripunctata was first described by the French entomologist and former president of the French Entomologist Society Amédéé Louis Michel le Peletier in 1836. Although originally placed in the genus Trigona, more recent taxonomic evaluations have since placed it under its current genus, following the 1943 work of Padre J.S. Moure, occasionally referred to as “the Father of Brazilian Bee Taxonomy.' However, some still consider the term Schwarziana as a subgenus rather than genus and instead incorrectly classify it under the closely related genus Plebeia. The closest relative of S. quadripunctata is the species Schwarziana mourei, determined through morphological and genetic evidence collected in the early twenty-first century. Until recently (2015) it was believed that these were the only two existing species under the genus Schwarziana in the world. However, two more species were discovered in the high altitude environment of South America – S. bocainensis in southeastern Brazil and S. chapadensis in central Brazi. The stingless bee S. quadripunctata varies in size from 6.0 to 7.5 millimeters. Worker bees and dwarf queens tend to be on the lower end of this spectrum while queens tend to lie on the higher end. Dwarf queens and workers tend to have an average weight of about 30 mg, but have been known to weigh as much as 40 mg or as little as 22 mg. Mated queens (those in charge of the nest) are, in comparison, much larger. The average queen bee weighs in at about 130 mg. However, some have been measured at over 160 mg, about a quarter of the weight of an average paperclip. Colonies contain a larger queen with greater fecundity than dwarf queens, causing the size discrepancy between the two. Unusual for most other eusocial insects, worker bees and dwarf queen bees tend to be similar in weight and size. The bees have a pale coloration of brown or reddish-brown with occasional yellow markings on the head. They maintain a punctate thorax and abdomen and a dorsal thoracic area sporting a few hairs. Glands are present on the head and thorax. The glands are larger in the heads of general worker bees and larger in the thorax for nursing worker bees. Nests are entirely underground on the subtropical floor and consist of vast and expansive cavities. Each nest is occupied by a single colony consisting of an individual queen and several thousand workers. Brood cells are arranged in spiral combs, each housing only one individual. Cells housing queens are typically much larger than the surrounding cells housing males and workers. The distribution of S. quadripunctata ranges from the central highlands of Brazil down towards the northern edge of Argentina on the eastern side of South America. Here, the environment consists of a wide variety of biodiversity living within lush tropical and subtropical rainforests. Altitudes can reach up to fifteen hundred meters (1500 m) in some areas. Lying so near the equator, temperatures are fairly warm year-round, averaging twenty-five degrees Celsius (25 °C). Nests are built into the fertile topsoil of the subtropical rainforests. The niche breadth of S. quadripunctata includes a wide variety of flowering plants that overlaps with many other eusocial bees native to the area, including members of the tribes Meliponini and Trigoni, as well as Africanized honeybees. Each nest features a single, simple rounded entrance, as opposed to a triangular entrance or one with a tube network, several layers, or multiple openings. S. quadripunctata nest entrances in São Paulo, Brazil consisted of an average entrance area of 14.5 square millimeters (mm2), relatively small compared to the 2.1 square millimeter (2.1 mm2) body of the bee. This may account for the lower traffic levels of the stingless bee through the entryway, an average of 17.4 bees per minute per nest. Members of this species are fairly common in their large South American region, with nests containing over several thousand members each. However, their population is believed to have declined by nearly sixty-five percent (65%) over the past few decades due to competition with the introduced Africanized honeybees along with human deforestation. This decline is projected to continue into the future.