Manual for Diagnosis of Screw-worm Fly - xcs consulting

A Manual for the Diagnosis of Screw-Worm Fly
When gravid or nearly so, female C. bezziana search for suitable hosts on which to oviposit.
Experiments in Papua New Guinea in which radioactively labelled flies were released from
locations 15, 25, 50 and 100km distant from traps and sentinels, labelled egg masses were
recovered from host animals at all distances, suggesting that host-seeking behaviour may
involve strongly dispersive activities.
2.2 Oviposition
C. bezziana females oviposit on the dry edges of wounds, depositing several layers of eggs
in a compact mass cemented together in an oval plaque (Fig. 5, Plate 1). The average time
taken to lay an egg mass is 4.1 minutes. In the hot, dry country around Port Moresby in Papua
New Guinea, oviposition occurs in the late afternoon and evening, continuing until dusk, with
some individuals completing oviposition in the dark (Spradbery 1979).This behaviour ensures
that most exposed egg masses are not subject to lethal amounts of solar radiation. Second
and subsequent egg masses can be laid at 4 day intervals (at 28ºC) with the protein
necessary for egg development being acquired at the oviposition site when females feed
on the wound fluids (Fig. 5) (Spradbery and Schweizer 1979). Females rarely lay more
than two egg masses under field conditions.
2.3 Incubation period
Under experimental conditions, eggs of C. bezziana hatch in 10.5 hours at 37ºC, 20 hours
at 27ºC and 50 hours at 20ºC. On host cattle, egg masses were observed to hatch between
12 and 20 hours (mean, 15.5 hours) after they were laid.
Figure 5: Oviposition by Chrysomya bezziana
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