Natural Enemies and Insecticides That are Detrimental to Beneficial Syrphidae

Abstract

SYRPHIDAEFlies in the family Syrphidae, called syrphid flies, flower flies, sweat flies, hover flies, or drone flies, belong to the order Diptera, suborder Brachycera, section Cyclorrhapha.They are small, medium, to large flies, smooth or pilose, dull to brightly colored.Many of the most common species are distinguished while in flight by their darting movements and their suspended flight above flowers, whereby they have acquired the name "hover flies."Almost all types of bees, bumblebees, social wasps and solitary wasps are mimicked by syrphids, and so often does this occur throughout the family that they form one of the most striking examples of what appears to be protective mimicry.The resemblance is complete in some species even to a humming sound while in flight much like that of a bee.The resemblance of Xylota chalybea (Wied.) to some of the black hunting wasps is complete, even to a rapid twitching of the wings when resting or moving about on the ground.Adult syrphid flies may be found almost anywhere, and some are quite common.Most of them visit flowers in sunny spots, but some occur only in woods, in moist places, in fields, or near ants' nests, depending upon their feeding and oviposition habits.Almost any locality, except arid ones, should yield nearly one hundred species over an extended period of persistent collecting, notably during the spring and early summer months.Several state check lists exceed two hundred species.In economic importance the Syrphidae comprise one of the foremost families of the Diptera.The adult flies of this family are considered by some authorities to be second only to honeybees in importance as pollinators.It is the author's opinion that their importance in this respect varies with the locality, with the plants to be pollinated, and from year to year, bumblebees and other Hymenoptera often being of greater importance in effecting pollination.Adult syrphids frequent flowers and feed upon nectar and pollen.Various species visit many of the same plants frequented by bees, wasps, skippers, and tachinid flies, transporting pollen from flower to flower as they go.It is difficult to measure the great service thus performed.In addition, the larvae of syrphids of several genera are predaceous on aphids and certain other Homoptera.They are generally rated second to the ladybird beetles among the aphidophagous predators.A few species attack Psylliidae (= Chermidae), Cercopidae, and lepidopterous larvae.Ewing (1914) included syrphids in a list of 14 natural predators on the common red spider, or spider mite, Tetranychus telarius L.The family is a beneficial one, except for a few species wherein the larval stage is injurious to growing bulbs and a few other plants (Wilcox, 1927).Medical annals record several scattered cases of myiasis caused by syrphids larvae, particularly those in the rat-tail maggot group (James, 1947).Based on his extensive studies in California of Syrphidae and their parasites, Kamal (1926a) stated, "The aphis-feeding syrphids rank as high, and under certain conditions higher, than our common ladybird beetles in their efficiency as plant lice enemies.On account, therefore, of the usefulness of these flies, a study of their natural enemies is of unusual importance from an economic standpoint."Fluke (1929) ranked Syrphidae first among the natural enemies of the pea aphid, Macrosiphum pisi (Kalt.),followed according to their importance in this respect by Coccinellidae, fungus diseases, Aphidius (Braconidae), and Chrysopidae.