Numerical investment in sex and caste by stingless bees (Apidae: Meliponini): a comparative analysis - Santos Filho, Persio de Souza; Alves, Denise de Araujo; Eterovic, André; Imperatriz-Fonseca, Vera Lucia; Kleinert, Astrid de Matos Peixoto (Apidologie, 2006)