I’ve never heard of this. It is a good question for your local Agricultural Agent.

And, here's the answer from a Texas A&M Horticulture PhD Extension Specialist. These folks are good! If you have a question that demands a little more insight than that of, say, a Master Gardener, they'll pop it up to someone with expertise in the matter.

"It is true that all domesticated cucurbits have cucurbitacins at very low levels generally at the 0.1 to 0.3%. They are mostly found in the leaves and stems followed by roots and fruit. Generally, plant stresses such as hot temperatures and lack of water can increase the amount in the fruits. There are differences between summer squash, winter squash, watermelons, cucumbers and other melons and even between varieties within these cucurbits. So, the bitter taste is due to these compounds and people can get sick if they eat a bitter tasting fruit due to the actual planting stressing due to the environment and increasing the levels in the fruit. Generally, these domesticated cucurbits are safe to eat but consumers should avoid any bitter tasting fruit and generally the rind is not eaten except for cucumbers and summer squash. For cucumbers removing the skin helps reduce these compounds and burpless varieties contain less as well as cooking them like summer squash reduces the active component. "

Thank you, Dr. Anciso!

I learned something too - thanks!

This made me recall some surprisingly bitter organic yellow squash I bought once upon a time. I thought it was old.