To tell the difference between the male and female Brassica butterflies just count the dots on their wings.  The male has one dot and the female has two.  We figured out an easy way to remember this.  The word "male" is one syllable and the male has one dot on each wing.  The word "female" is two syllables and she has two dots on each wing.

Male Brassica Butterfly

Female Brassica Butterfly

one dot on each wing two dots on each wing