Manual for Diagnosis of Screw-worm Fly - xcs consulting

A Manual for the Diagnosis of Screw-Worm Fly
Third Instar (Figs. 12,17)
Third instar larvae are 6.1-15.7mm long and 1.1-3.6mm in diameter. Young third instar larvae
are whitish to cream coloured with mature larvae developing a pinkish colouration. The heavy
bands of dark, robust, thornlike spines are very prominent. The anterior spiracles are nonfunctioning
(occluded) with 4-6 lightly sclerotised (pale brown) papillae or branches. The
posterior spiracles are each surrounded by a heavily sclerotised peritreme (dark brown to
blackish) which is incomplete ventrally, and with 3 slit-like spiracular openings at
approximately 45º to the horizontal.
3.4 Puparia (Fig. 9)
The mature larva, after burrowing into the soil, undergoes a process of pupariation during
which the cuticle of the larva becomes heavily sclerotised. In the early stages of pupariation,
the larva contracts its longitudinal musculature thereby shaping the puparium. The colour
changes from deep pink, through brown and finally to almost blackish brown as sclerotisation
is completed. The ends of the puparium are rounded with the anterior end a little more
pointed. Some of the characters observed on the cuticle of the third instar larvae, especially
the bands of spines, are retained in the surface structure of the puparium.
The puparium is up to 10.1mm in length and 3.6mm in diameter.
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