We assessed the effect of two social constraints, density and OSR, on the expression and relative importance of female choosiness and male PLX4032 on mating outcome. We recorded male and female behaviours in densities and sex ratios covering the range of experimental conditions previously used in all laboratories working with this species (Fig. 1a). Thus, three densities (high: 0.44–0.45; intermediate: 0.065–0.067; low: 0.003–0.016 individuals/dm3) and three sex ratios (75, 50 and 33% of males) were tested in a crossed design. We accounted for the potential confounding effects of cage size on butterfly behaviour by creating treatments with identical densities and sex ratios produced using variable numbers of individuals in three cage volumes (small cylinder: π × 1.52 × 3.8 dm = 27 dm3; medium parallelepiped: 12 × 6 × 7 dm = 504 dm3; large parallelepiped: 420 × 190 × 215 dm = 17?157 dm3; Table 1, Fig. 1b). The design resulted in 14 different treatments and the radiometric time number of replicates per treatment varied from one to four (Table 1). Potted maize plants were present in the small (one plant), medium (four plants) and large experimental cages (10 plants) to allow perching and hiding. The 20 experimental trials were carried out with two cohorts from 25 April 2012 to 8 May 2012 and from 17 to 29 June 2012.