Outside? Interesting...it has always been kept indoors - only had it 2 years now however. What formulation of sevin would you suggest? The same as for any outdoor shrubs, etc.? Is it likely that all the leaves will drop again? That's what happened a few months ago when the mealybugs got ahold of it. Thanks!!
"it has always been kept indoors"
which is probably why you're having problems. Slow decline, with an apparently sudden collapse is not unusual for "indoor" trees. Privet is an extremely tough plant--when it's outside. Indoors, drastically limit the amount of light it gets, as well as air circulation. Add to that constant overwatering (which the dense soil only makes worse) and even the toughest plant will eventually die.
Dropping leaves and insect infestations are markers of a weak tree.
Get it outside ASAP. You haven't provided your location, which is critical here, do you get winter weather?