[JayG]

That's unfortunate - finding a caterpillar inside one ovary but not the other doesn't tell us whether it was the actual cause, or taking advantage of the damage caused by something else.

If it keeps happening, keep checking them, but the fact your other squashes are OK does potentially support the theory of too much heat for that particular variety (assuming it's being grown in similar conditions.)

You may have better luck when it cools down a little if the plant is still flowering.

[LotuSeed]

It's been 90+ here most of Spring and all of Summer. My pumpkins have not suffered from the heat. I have several varieties of pumpkins and one unknown variety of squash growing well. All of them put out male flowers first, sometimes for a while, and then put out a few female flowers. Not all of the female flowers have matured, in fact I think that for each mature fruit I have gotten, I've had at least two that never made it past the flower stage. The bud will only open for pollination if conditions are right for the plant to carry it through to maturity, at least that's my experience. I prematurely opened one in order to hand pollinate it and it ended up rotting. If the female flowers are appearing but staying tightly closed, then they are not going to get pollinated and are going to rot. Sometimes it takes a few duds before you get one that will actually open and set.  I'd be patient and check for new flowers daily. 

[surbie100]

I've picked off another 6 today.  Am guessing it was from the recent cold and rain, though I have 6 flowers which look hopeful. I count squashes rather obsessively...

[Justniv]

thank you all for trying to help...