What kind of insect? Recommendations will differ for different pests, and indiscriminate, "kill everything" style spraying is a thing of the past (thank goodness!)

Insect that spoils the fruit of stone -fruits (eg plums) is the Mediterrenean fruit fly when the fruits already set.Insecticide spray should be used after fruit set,not during flowering stage.At this stage,the beneficial insects,like bees,would have already done their sterling job.Harmful insects would try to come along ,but the smell of such spray repels them as long as spraying is reapeated ever 3 weeks.