Bionomics and Physiology of Aphidophagous Syrphidae

Abstract

The Syrphidae belong to the cyclorrhaphous families of Diptera. The feeding habits of their larvae are varied, some being carnivorous, other phytophagous, and a third group acting as scavengers in various media. Representatives of various genera devour aphids, these carnivors are some of the most effective biological agents which cause premature mortality of their prey, and they are beneficial insects which must be considered in pest control. However, the management of Syrphidae in biological and inte­ grated control is not an easy task because of their relatively high ecological demands on the environment. Larvae and adults have different diets ; the adults feed not only on honeydew of aphids but also on nectar and pollen. Uptake of pollen is a prerequisite to normal ovarial function and fecundity. Landscapes or seasons without flowers hamper their ecological and econom­ ical efficiency. Many species are swift and indefatigable fliers. The adults can easily escape from inadequate environments. Theoretically they could shift periodically from feeding to breeding sites over great distances but ex­ perience indicates that they prefer areas with flowers even for oviposition. Univoltine species overcome a shortage of food during summer and autumn by entering into diapause at the end of larval growth. Every biological and ecological work is based on the identification of the species in question. In addition to the usual handbooks and keys, some papers of recent date should be mentioned. The classification of the Syrphi­ dae, according to natural relationships (for instance the limit between the species Syrphus and Epistrophe), has not yet been definitely concluded (36, 44) ; a distinction should be made between genuine characteristics of species and variations in color in the S phaerophoria species (4). Living old larvae show surface structures and subcutaneous colored markings typical of their species, so that identification is possible in most cases already in this stage (13, 22, 29, 32-34, 48, 61, 73). Scott (78) published a key for the identifi­ cation of the pupae of 28 aphidophagous syrphids. Even the chorion of the eggs shows specific characteristics (28, 78). However, the establishment of any comprehensive key for the identification of eggs seems to be doomed to failure owing to the fact that the structure of the eggshells of closely re­ lated species (for instance, Syrphus ribesii, S. vitripennis, S. torvus), or