An Investigation of the Life Cycle, Ecology, Anatomy and Morphology of the Hover-Fly Syrphus novae-zealandiae Macquart (1855)

Abstract

One thousand nine hundred and sixty adults of S. novae-zealandiae were examined during the years 1954-1955, and of these 73.4% were females and 26.6% males. This percentage composition of the sexes and the periodic fluctuations in the population appear to be a constant feature. All these flies were caught in cultivated areas, none being taken in truly native plant associations which formerly they were stated to inhabit. In the absence of an endemic aphid fauna in New Zealand, it is believed that in the past the now aphidophagous S. novae-zealandiae met the requirement of its life-cycle on the Psyllidae and Jassidae; though at the present time it carries out its life-cycle on the many introduced aphids, 54 of which have now become established in New Zealand. The complete life-cycle takes only about 18 days in summer, and a maximum of 42 days in early spring. Larval instars are not clearly defined by ecdyses. The larvae are subject to parasitic attack of an introduced ichneumonid Bassus laetatorius. Thoracic plates have been extensively studied and sorted out, providing a basic pattern for any future discussions in the group. Sexual dimorphism is significantly marked in the size and structure of the eyes, pulvilli and the post-abdomen. Anatomically there is little difference from the more generalised Diptera such as Musca domestica or Calliphora erythro-cephala. The presence of a large dorsal accessory metathoracic nerve is noted. The reverse order of spermathecae in the female reproductive organs is recorded. The fusion of the tergum and sternum in segment IX into an indistinguishable plate is described.