CHAP. XII - Diptera (contd.)

Summary

Family Syrphidae

Mostly brightly coloured flies of moderate to large size; in the wings there is a second margin parallel with the outer wing margin formed by certain other veins, and also a false vein or’ vena spuria' between the radius and median. The group is an important one owing to the aphis-eating habits of certain species. Three members of this family attack narcissus bulbs and occasionally onions, parsnips and potato, and are in consequence shortly dealt with here.

Merodon equestris F. The Large Bulb Fly

DESCRIPTION. Adult. Large hairy flies of bee-like aspect.

Male. Head, eyes brown, with short yellowish pubescence, contiguous for about half the length of the frons, ocelli brown, distinct. Face with bright shining pubescence, antennae dark brown to black. Thorax shining black with thick pubescence which varies greatly in colour from all tawny to tawny on first thoracic segment with black on remainder. Abdomen shining black with long thick pubescence varying in colour from all black to black and tawny or all tawny. Legs black; hind femora slightly dilated; hind tibiae dilated with a spur at the tip. Wings clear, without markings, veins blackish, squamae large with a fringe of long hairs, blackish or tawny. Halteres small, concealed.

Female. Eyes not contiguous, frons widening. Pubescence on thorax usually all black. Length 10-12 mm.

Egg. Oval, chalky white. Length i-6 mm.

Larva. The mature larva is yellowish in colour, robust, somewhat rounded, segmentation distinct. Anterior spiracles brown, posterior spiracles black, somewhat raised. On each side is a short spine. Length 12-18 mm.

Puparium. Light to dark brown in colour. The anterior spiracles remain as a pair of horn-like processes, and the posterior spiracles as a black projection. Length 12 mm.

LIFE HISTORY. There is one generation per annum, the eggs are deposited singly in the soil or on the base of the plant, hatching in 6-15 days. The larva enters the bulb between the scales where it feeds; there is usually only one larva in a bulb. Pupation takes place in March or April, usually in the soil but occasionally also in the bulb. The flies are on the wing from May to July. Host plants are mostly narcissus bulbs; but the insect is also recorded from Amaryllis, Galtonia, etc. Theobald has found it attacking the wild hyacinth (Scilla nutans).