I did a great Bat Mitzvah last year in the Hamptons and it was an awesome outdoor event. However, just before start time a swarm of bugs came flying in like a kamikaze fleet. They were out for us and all the guests soon to arrive. Luckily my staff went out and bought 

a slew of bug spray for the attendees to use.  We also lit our tiki torches (all 20 of them) to combat the attack. It worked and the threatening swarm seemed to disperse in a half hour or so. 

Lesson learned? Be prepared for those little flying party spoilers. The best way is to have your property sprayed a day or two before the party. Ask your landscaper about an organic option that is made up of rosemary and mint oil. Its safer than the conventional insecticide and smells great! Another great option is to put a bottle of bug spray in the bathroom(s) for your party goers to use. Again, try to get a nice smelling one so all your guests don't start reminiscing about their last camping trip. OFF makes a nice Tropical or unscented spray.

One more tip, NO chocolate fountains outside!! Its like having an all banana buffet for a group of ravaging monkeys. Go for chocolate covered strawberries if you need that fix. EVEN better, serve frozen chocolate covered bananas on a stick!