REGENTS QUESTION ON BIOLOGY!!! I need help on this difficult question, read it...

[musicprincess4ever]

...below.? Growers of fruit trees have always had problems with insects. Insects casue visible damage to fruits, making them less appealing to consumers. As a result of this damage, much of the fruit cannot be sold. Insecticides have been useful for controlling these insects, but, in recent years, some insecticides have been much less effective. In some cases, insecticides do nothing to stop the insect attacks. Idenify the original event that resulted in the evolution of insecticide resistance in some insects. PLEASE EXPLAIN HOW YOU GOT YOUR ANSWER. THANK YOU SO MUCH!!!!!!!!