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Sexing Monarchs

LARVAE

The sex of monarch larvae can be determined only in dissection. Males will have a testis located in the 6th abdominal segment, dorsal to the gut. If you have a last instar male caterpillar, the testis will appear as two bright red or pink sacs; often they appear to be one sac.

PUPAE

To determine the sex of pupae requires only keen eyes or a dissecting microscope. Surrounding the cremaster (the structure from which the pupa hangs) are a series of rings, called abdominal sternites. Within the first ring (9th abdominal sternite) are several paired black dots next to the cremaster; turn the pupa so that you are looking at these dots. If the monarch is a female, the ring adjacent to the 9th sternite will have a line dissecting it; this line (indicated by the arrows on the photo and diagram below) will be centered between the pairs of dots. Male monarch pupae do not have this line.


Diagram of a monarch pupa

Diagram modified from: Hughes, P. R., C. D. Radke, and J. A. A. Renwick. 1993. A Simple, Low-Input Method for Continuous Laboratory Rearing of the Monarch Butterfly (Lepidoptera: Danaidae) for Research. American Entomologist 39: 109-111.

ADULTS

Male Monarch image

 

 

Male Monarch: Notice the thin vein pigmentation and swollen pouches on the hindwings.


Female Monarch image

 

 

Female Monarch: Notice the thick vein pigmentation and no hindwing pouches.

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