Re-skimmed a lot of Sex, Color and Mate Choice in Guppies by Anne E. Houde. Reporting on research involving wild-type guppies, she suggests that the behaviors of virgin guppies are different than those of the more choosy females who have already given birth to fry. Neither the younger virgins (age 2 months to maybe a couple of months older) nor the full grown virgins (4-6 months old?) were as adverse to the advances of male guppies. In fact the older virgins were the most responsive. Evidentially they can get pregnant throughout that time period.

If the males went into their dances, those sigmoid displays, responsive females would slow down their swimming into kind of a "glide response." That showed their interest without turning towards the male, which might be interpreted as an aggressive response to the smaller male. Mating didn't automatically follow, but that would be the first step in that direction.

That doesn't answer the question, when can an older virgin female still be viable? Again I am embarrassed to not know. I have almost never had to worry about getting selected guppies to reproduce, so the question never came up.

By the way, Houde's book is on sale again in hardback at
http://search.half.ebay.com/guppies_W0QQmZbooks

Stan Shubel, in his book, does allow as how sometimes a female from a batch doesn't work out as a mother and how he would go back to get a sibling and see if she was satisfactory. I'm guessing he could be working with a five-six month old guppy. If I had gone to that Chicagoland guppy show this weekend, I would have asked around.

"Nate" who sometimes graces Guppylog, had noted elsewhere and under another name that there comes a point where unmated female guppies can't be impregnated. That point was raised with miskairal and she discovered that her unmated females of over a year in age, would always remain that way.

Miskairal's discussion is at:
http://www.guppylog.com/?op=displaystory;sid=2005/2/23/23535/0819

I'd have gotten to this sooner, but I took my lady to a nice restaurant to celebrate our anniversary the other evening. Sometime later I noticed a considerable difficulty in breathing. A quick inspection in a mirror revealed a gorgeous red hue to my face and upper torso. The face but especially nose and lips were swollen to an extend that only a momma camel could love. The swelling of the tongue and constriction of the throat suggested that I had less than an hour to swing by a local emergency room or the camels and I would both be out of luck. They did a fine job of pumping the appropriate medications through an IV unit. But it has been a couple of days before I felt comfortable "running moving machinery" and catching up on everything waiting on the computer.

Never had an allergic reaction to food before. (Rats, another warrenty running out.)
So much for fresh shrimp scampi. :(
But I thank God for the chance to be back. :)