I recently propagated a Golden Pothos -- took 2 nearly identical cuttings and placed them both in water. One however, was treated w/ a 24-7-15 plant food and in the other, I discovered a small dead bug had trapped itself in the container. Oddly, the one w/ only water and a bug already started roots whereas the other who was given plant food has yet to show anything.

I've Googled this question w/ no results and wonder if anyone has any insight into this?

Thanks!

would need to duplicate this with several to come to any kind of conclusion on it.
Possible the nutrients from the bug decomposing fed the plant.

Agreed. Would certainly need to replicate for conclusion. But, how likely is it that the bug is feeding the plant?

Any personal experience with this sort of thing?

well there are nutrients in the decomposing body of the insect which the plant may have used. I would say very likely.

What kind of bug and how big was it? A big roach maybe would have enough nutrients in its decaying body to feed a cutting a little bit. But I'd have to say I'm doubtful that this will work dependably. I start cuttings of all sorts of plants in water, some make roots right away and some take weeks or months. Depends mostly on the cutting, where it came from on the mother plant, what stage of growth it's at, the temperatures (all mine are outdoors) and light levels.

I've put 5 cuttings of my Brugmansias in one jar of water, left them on the patio table and had some make roots right away, some sit happily with perky leaves and no roots, and some rot and die, all in the same jar, all from the same pruning of the same plant on the same day. Begonias the same, some make roots immediately, some wait weeks.

decomp does add nutrients, but over a LONG period of time. The bug isn't just dissolving nutrients into the water. Fungi and bacteria are decomposers, they will consume chemicals from the dead things and produce waste which is used as nutrients for other things. Plant decomp can happen much faster and provide nutrients for other plants much more quickly than bug or animal decomp, but even then.. just having a dead plant in the water is unlikely to provide such an immediate result.

Pothos cuttings do not need or benefit from nutrients in the water. The bug and the fertilizer are both irrelevant to root development. If both had been placed in plain water, you would have gotten the same results.