RESUMEN
Applications of Juvenile Hormones JH I, II and III in single or fractionated doses to larvae of Melipona compressipes, Melipona quadrifasciata, Melipona rufiventris and Melipona scutellaris at the L3 and beginning of cocoon-spinning phase (pre-defecating larvae - LPD) activated feminizing genes, inducing differentiation of female larvae into queens. The technique of fractionated treatment proved to be highly efficient in Melipona species for producing of queens. It is difficult to obtain 100% queens with single dosage of JH in some species which implies in a mechanism of JH degradation by specific esterases. One hundred per cent of queen production occurs only when an adequate amount of Juvenile Hormone is administered within the period that is critical for caste determination. The threshold dosage of JH I for Melipona compressipes (below which it is not possible to obtain 100% queens) was 0.1mu JH I 4 applications of 0.25mu g each. For Melipona quadrifaciata the threshold dose for obtaining the highest proportion of queens was 0.2mu g JH I in 4 applications of 0.05mu g each. For Melipona scutellaris 0.025mu g JH I/mj 1 in single dosage induced 100% of queens. No 100% production of queens in Melipona Rufiventris treated larvae were obtained; the highest proportion was 86% of queens with 0.2mg g JH I/mu 1. In order to obtain expression of the feminizing genes in Melipona species, JH I was the most efficient followed by JH III. Each species respond differentialy to JH dosage, and this dosage must be tested before use.