Botanical origin and seasonal variation in pollen collected by Tetragonisca weyrauchi (Apidae: Meliponini) in an urban area of Rio Branco, State of Acre, Brazil

Abstract The botanical origin and seasonal variation of pollen collected by Tetragonisca weyrauchi were studied by means of palynology (pollen identification). The study was carried out between August 2016 and July 2017 with a hive introduced in a house garden in an urban area (09° 56′ 38.7″ S; 67° 52′ 42.9″ W) near the campus of the Federal University of Acre (UFAC). In total, we identified 87 pollen types from 31 botanical families, with the most representative ones being: Alismataceae, Amaranthaceae, Arecaceae, Boraginaceae, Cyperaceae, Euphorbiaceae, Fabaceae and Urticaceae, all displaying percentages above 10%. The pollen types Alternanthera (Amaranthaceae), Cecropia (Urticaceae) and Cordia sellowiana (Boraginaceae) obtained relative abundances above 90% and are therefore considered events of temporary specialization. The lowest diversity and evenness values were found for July (H′ = 0.127; J′ = 0.071) and August (H′ = 0.070; J′ = 0.043), and the highest values for October (H′ = 2.025; J′ = 0.715) and April (H′ = 1.941; J′ = 0.611), thus not suggesting relationships with the rainy (November–April) or dry (May–October) periods. Furthermore, there was no preference by the bees for morphological characteristics of the pollen such as size, exine texture or aperture number. However, the most representative grains are among the small and medium size, reinforcing the hypothesis that this bee species prefers small flowers available in dense inflorescences.