The most effective way to rid your crops of fruit bats, or flying foxes, is to make it impossible for the animals to access them. If you benignly demonstrate to your bats that you mean business, they'll take their business elsewhere. In the meantime, try to think of the presence of fruit bats in a positive light. The bats are there to eat not only the fruit, but the bugs that plague your plants. Then they excrete what they've eaten and digested, which fertilizes your plants.
Examine the evidence to determine that bats are the culprits. Fruit damage is inflicted by a range of other pests including birds, fruit flies, rats and opossums. Look for whole or partial fruits dropped on the ground beyond the tree's canopy. Inspect partially eaten fruits marked by distinctive scrapings from sets of large canine and tiny front teeth. Poke around under the tree or shrub for telltale little balls of fruit pulp and squirty droppings. These are all unique indicators of bat plundering.
Pick fruits a day or two early before they mature completely. Fruit-eating bats prefer their meals ripe or overly ripe.
Cover individual fruits with paper bags if you can reach them safely.
Drape the foliage of attractive fruiting plants with bird netting.
Hang annoying, distracting objects from and near your fruiting plants. Use anything highly visible that moves easily or makes noise. Strips of aluminum foil, wind chimes, suncatchers, old CDs and windsocks are effective. Alternate objects and their positions often.
Send the family dog out to earn his keep in the affected area. The bats won't appreciate his presence if the pet is persistent.