Manual for Diagnosis of Screw-worm Fly - xcs consulting

A Manual for the Diagnosis of Screw-Worm Fly
1.1 Geographical distribution
C. bezziana occurs throughout tropical and subtropical Africa, the Indian subcontinent and
much of southeast Asia from Taiwan in the north to New Guinea in the southeast (Norris and
Murray 1964). Within Papua New Guinea, SWF occurs throughout the mainland to an altitude
of 2,590m, and in New Ireland, New Britain and the offshore island of Daru in Torres Strait.
This species does not occur in the North Solomons Province of Papua New Guinea and has
not been recovered from any Australian islands in the Torres Strait. C. bezziana was
accidentally introduced to Bahrain in the Persian Gulf in 1980, probably from Oman or the
United Arab Emirates where C. bezziana is endemic, via shipments of live sheep (Kloft et al.
1981, Rajapaksa and Spradbery 1989). In 1996, a major outbreak of C.bezziana was
recorded in Iraq, a country in which SWF had not previously been recorded. C.bezziana has
also been recorded in Ethiopia and is probably widespread in the Horn of Africa.
Australia remains the only continent with a tropical climate which is free of SWF, in spite of its
close proximity (150km across the Torres Strait) to neighbouring Indonesia and Papua New
Guinea where SWF is endemic. The only recorded incursion took place in April 1988 when
several adult C. bezziana were recovered from a light (electrocutor) trap aboard a livestock
vessel in Darwin harbour (Rajapaksa and Spradbery 1989). The ship had just returned from
offloading cattle at Brunei.
1.2 Potential distribution of C. bezziana in Australia
The distribution of C. bezziana and Co. hominivorax is limited primarily by the inability of SWF
to survive cold temperatures. In Co. hominivorax adult activity decreases below 20ºC and
where mean temperatures are 9ºC for three months or 12ºC for five months, SWF
cannot survive (Paman 1945). Cooler temperatures result in such prolongation of the pupal
stage that at 13ºC pupation occupies 8 weeks compared with 7 days at 28ºC. Nevertheless,
pupae can survive brief periods at -9ºC and adults at -7ºC.
C. bezziana adults have been recorded dispersing up to 100km (Spradbery et al, 1994) and
Co. hominivorax up to 290km (Hightower et al. 1965). The strongly dispersive behaviour of
adults, together with livestock movements, would probably result in rapid colonisation of
vacant areas.
Figure 1: CLIMEX predictions for distribution of Chrysomya bezziana in Australia. A - permanent
colonisation, B – summer occupation. The relative climatic favourableness of each
location is proportional to the area of the circle (from Sutherst et al. 1989).
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