Biology, morphology and anatomy of aphidophagous syrphid larvae

Abstract

The paper deals with the biology, morphology and anatomy of seven species of syrphid larvae viz. Syrphus luniger Meig., S. balteatus De Greer, S. ribesii Linne, Catabomba pyrastri Linne, Sphaerophoria flavicauda Zett., Sph. scripta Linne, and Platychirus scutatus Meig.The habitat, mode of progression, aphidophagous habits and characteristic coloration are described for each species.It is shown that the larvae of all the above species, like larvae of other cyclorrhaphous Diptera, definitely pass through three stages separated by two moults. The mode of dehiscence of the puparium is described briefly.Each of the species, except Catabomba pyrastri, has three generations in the breeding season which lasts from May to October. Platychirus scutatus hibernates only in the larval stage, but the other species may be found in both the larval and pupal stages during the winter.The larvae of all the above species, except Syrphus balteatus, are commonly parasitized by ichneumonid larvae.The morphology of the egg, the three larval stages and the puparium of S. luniger is described in detail.The characters common to the third stage larvae of all the species dealt with are summarized and short descriptions of the third stage larvae and puparia of the individual species are given. The general appearance of the living larvae and details of the buccopharyngeal armature, spiracles and puparia of each of the species is represented in figures.In connexion with the pupae a number of new structures are described and it is suggested that some of them are concerned with the formation of the characteristic shape of the puparium and with the dehiscence of the puparium.Internal pupal spiracles are present in all the species dealt with, but external pupal spiracles are present only in Platychirus scutatus.The anatomy of P. scutatus is described and figured, an account being given of all the structures except the musculature of the body wall. Study of the anatomy affords evidence as to the carnivorous mode of life of the larvae and also indicates that the larvae have evolved from aquatic forms.The comparative morphology of the Syrphinae is discussed with respect to the relationship of the Syrphinae to other Aschiza and to the cyclorrhaphous Diptera.