Milky Spore: Depends on how many times is occasional and when it is applied.
Milky spore needs the grubs to survive and multiply. so if you kill a big percent of the grubs then it reduces the amount and effetiveness of Milky spore. do this mutiple years and ......... Apply another insecticied at the time there are the least Japanese grubs in the soil if you can depending on what it is your trying to control. If it is grubs, then identify them as which beetle. If japanese beetle then no other insecticide.