Manual for Diagnosis of Screw-worm Fly - xcs consulting

A Manual for the Diagnosis of Screw-Worm Fly
3. Description of life stages
3.1 Adults
Adult C. bezziana are metallic blue, bluish purple or blue/green in body colour with
predominantly orange coloured heads and burgundy-coloured eyes (Plate 7). The hind
margins of the abdominal tergites are black, giving the abdomen a slightly striped
appearance which is more obvious in C. bezziana from Africa (see Fig. 31). In females the
compound eyes are widely separated but in males, the eyes are virtually touching dorsally
(Fig. 10). The frontal stripe of females is parallel sided and diagnostic for C. bezziana (Fig.
10). The ovipositor and associated sclerites of C. bezziana are markedly shorter than closely
related, similar-looking species of Chrysomya (see adult key).
The size of adults varies, depending on the feeding regime during the larval stages. Body
length is up to 10.0mm and head width up to 4.1mm.
male female
Figure 10: Head of male and female Chrysomya bezziana. Note that the compound eyes nearly
touch in the male and both sexes have a marked “excavation” in the cheek area.
3.2 Eggs
The oval egg mass is brilliant white and firmly attached to the dry epidermis, or the exposed
dermis adjacent to a wound or injury of the host animal (Plate 1). The eggs are glued to each
other along their long axes with a dense secretion filling the spaces between the eggs which
may be in three or more layers. The eggs are characteristically laid parallel to each other,
giving the appearance of a shingled roof (Fig.11). The individual eggs are difficult to separate
from an egg mass without the use of chemical solvents such as dilute potassium hydroxide
(KOH). Egg masses contain from 95 to 245 eggs (mean, 180) although, if a female is
disturbed while ovipositing, two or more smaller egg masses may be deposited.
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