**2.3 Obtaining hybrids**

Mass crossings in both directions were performed in population boxes (16 cm3), using 200 couples, between NA-FS and MU-S, NA-FS and MO, NA-FS and AR and MU-S and MO. After setting up a cross, the courtship behavior was observed for 10 minutes, as described by Markow (1981). The culture media were placed in Petri plates at the bottom of the boxes and were changed every three days. After every plate change, the plates were inspected to detect eggs. The plates were maintained at a constant temperature of 20ºC ±1ºC until late third instar hybrid larvae were observed. These larvae were obtained directly from the plates and frozen at -20ºC for further electrophoretic analyses.
