The fruit grower might decide that protecting the fruit from maggots is more important and might apply a pesticide that also kills many of the syrphid flies. Populations of indirect pests, however, can be tolerated without harming the tree or crop. On apples, for example, an average of five or six mites per leaf can be tolerated. Only if the mite numbers exceed this threshold are sprays recommended. Other insects also are considered beneficial in the fruit planting.
Bees are beneficial since they pollinate most fruit crops.
Insecticides should never be sprayed when the crop is in bloom. Also, avoid the drift of insecticides onto other blooming plants when fruit crops are being sprayed. As mentioned above, many types of flies are predators or are parasitic on fruit pests. Syrphid fly larvae are typically maggot-shaped and legless, with a head end that is narrower than the tail end. These flies may be found foraging among colonies of aphids on the undersides of leaves.