Methoprene increases reproductive organ development and mating behavior in fall migrants. (A) Reproductive development is increased in fall migrants following methoprene treatment. Numbers represent the animals examined. Postmortem reproductive development was assessed for all migrants depicted in Figure 2; vehicle-treated migrants (blue bars) and methoprene-treated migrants (red bars). Reproductive development of male migrants (upper panel) was quantified by extracting and weighing reproductive glands (tubular gland and ejaculatory duct), while reproductive development of female migrants (lower panel) was quantified by counting all mature oocytes (that is, those with well-defined ridged chorion). (B) Mating behavior was increased in vehicle-treated migrants (blue bars) compared to methoprene-treated migrants (red bars). Numbers represent the animals tested. To assess mating behavior, male and female butterflies from each group were placed together in flight cages under high intensity light of 2.6 × 105 photons/cm2/s during the light period of LD at 25°C, and the number of animals in a mating pair was recorded over a 2-day period.