Sexing Nymphalis antiopa Pupae

After all our mourning cloak (Nymphalis antiopa) larvae pupated, we sexed the pupae.

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Now that all of our antiopas have pupated, we removed all the pupae from their substrates (branches, lid) and collected them in plastic containers. We could have left them hanging and have them eclose in their natural position which would likely result in less crippled butterflies, but collecting the pupae grants us the rare opportunity to sex and collect data from them.

Sexing Nymphalis antiopa pupae is quite straightforward and similar to sexing any Lepidoptera pupa in general - just inspect the sex marking at the ventral rear of the abdomen. As in other Lepidoptera species, the females have a long, distinct slit cutting through the center of the fourth and fifth abdominal segment past the wings. The male's sex marking, on the other hand, is contained only in the fifth segment, and is a small hole rather than a slit. The photos below show these markings. 

We were able to reliable sex the vast majority of our 157 pupae, though some of them were difficult due to deformities on the abdomen. We ended with 71 females and 84 males, with 2 that we were unable to determine due to severe deformities near the sex marking. The sex ratio is not quite even which is quite unusual for such a large sample size, so we may have misassigned some females as males. However, we double checked and it didn't appear that we had made any mistakes so we probably could have only misassigned a few at most. This underrepresentation of females could suggest that there were some unusual factors that increased female mortality, so just to verify whether or not the sex ratio is truly unreasonable or not, we decided to take the statistical approach.

The proportion of females is 0.458 and males is 0.542. A one-proportion z-test showed that the 0.458 female proportion is not significantly less than the expected 0.5 even with a sample size 0f 155 (z=1.044; p=0.148). So, looks like we simply got a bit unlucky with the low proportion of females, though it is not unreasonable extreme. 

After we had finished sexing the pupae, our next task was to weigh and collect the mass data to compare the male and females masses. See Nymphalis antiopa Pupa Mass Data.

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Authors
Alan Liang

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