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Hi all,

A known phenomenon with Purple Emperor larvae is that their sex can be determined when in the final instar based on the presence (or absence) of a pair of pale patches on the eighth segment that are the developing testes, indicating a male larva. I think I've just found a photo showing this in the Small White also. Does anyone else have anything similar? Thanks!
Cheers,

- Pete

Green-veined White too!
Cheers,

- Pete

Hi Pete,
I have seen this as well in both Small White and Green-veined White, but not just in their final instars. I have noted patches of colour (usually purple) showing up on the 8th segment (abdominal segment A5) of some larvae in their 4th instar.

Small White

Male larvae
Female larva for comparison Green-veined White

Male larvae
I have also had a quick scan of other species (concentrating on those that have green larvae) and Ben Smart's Small Skipper looked promising although the pale marks appear to be in the 9th segment (A6) rather than the 8th.
Vince

Wall Brown? There definitely appears to be a paler mark in the same area as the other larvae shown.
James

Thanks Vince and James!

Some interested thoughts from Mark Youles here: http://apaturairis.blogspot.com/2014/02 ... exing.html

Cheers,

- Pete

Going through my archive, I think that this final instar Silver-spotted Skipper may also show its developing testes.
Cheers,

- Pete

is this just for butterflies, or do moths eg Hawk Moth also show this. Although on the hairy larvae it would be very difficult to see. Im not sure if Glanville larvae do either will look later in the season.

MrSp0ck wrote:is this just for butterflies, or do moths eg Hawk Moth also show this. Although on the hairy larvae it would be very difficult to see. Im not sure if Glanville larvae do either will look later in the season.

The phenomenon seems most prevalent in species whose final instar larvae have few (or no) hairs and a pale ground colour, so I suspect it's seen in some moth larvae too, but I don't think you'd see it in a Glanville Fritillary larva for these reasons.

Cheers,

- Pete

I'm currently working on the Large Skipper species description and came across this 2nd instar larva - the first time I've seen anything that might hint at testes in anything other than a final instar larva!
Definitely a topic to be studied in more detail at some point!

Cheers,

- Pete

[Edit] Here's a 4th instar, also with the pale markings.

Lulworth Skipper
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We were working on the Emperor Moth larvae, and think the spotting in the last instar may be different sexes too, the pink and the yellow in the black bands, when we do the species again, the larvae will be sorted so adults emerge in different cages, to see if males and females are all in the same cages.

Are the marks on the same segments on the male pupae as the last intar larvae ? We have all been straining our eyes looking at moth pupae all these years looking for the 2 bumps/marks.

MrSp0ck wrote:Are the marks on the same segments on the male pupae as the last intar larvae ?

I don't think so - the testes always 'show' on the 8th segment, whereas the diagnostics for sexing of pupae is based on the position of the genitalia at the end of the abdomen (see http://www.ukleps.org/sexingpupae.html).

Cheers,

- Pete

And another example - Wood White, 4th instar!
Cheers,

- Pete

Fascinating stuff. I trust that this information will be included in your forthcoming work, Pete?

David M wrote:Fascinating stuff. I trust that this information will be included in your forthcoming work, Pete?

Thanks David. It does get a mention in the Purple Emperor description, but will probably become an article post-book!

Cheers,

- Pete

Thanks for that, Pete. Looks like this publication will help stave off the depression next winter.