Q.Cherry fruit is damaged with little bugs that eat their way out of ripe fruit and puncture skin. The flesh of the fruit disintegr
ates I guess the little creature starts life when the cherry is in blossom and has arranged its life cycle so it is ready to chew its way out of the fruit when the cherry is just about ripe. They come out of a small hole that they make. The skin once punctured is attacked by wasps and other insects.
When should I spray the cherry flowers and with what?
There are a couple of possible pests causing this damage.
These links will help you.
http://fruitandnuteducation.ucdavis.edu/fruitnutproduction/Cherry/Cherry_Pest_Deficiencies/Cherry_Insect_Mite_Nematode/
https://www.gardeningknowhow.com/edible/fruits/fegen/fruit-tree-spraying.htm