Distribution and pest status of the Old World screw‐worm fly, Chrysomya bezziana (Diptera: Calliphoridae), in Papua New Guinea and the threat to Australian livestock and wildlife

Abstract

AbstractThe distribution of the Old World screw‐worm fly Chrysomya bezziana Villeneuve and the incidence of traumatic myiases (strikes) in livestock, humans and wild animals in Papua New Guinea (PNG) for the period 1973–1985 is described as a foundation for current considerations of risk to Australia. Field studies indicated myiasis caused by C. bezziana occurred throughout PNG to an altitude of 2590 m. Cattle and sheep were the most commonly recorded hosts. The impact of strikes on individual cattle properties varied from negligible levels to every animal being infested on average each year. The incidence of strikes was apparently related to vegetation cover with fewer strikes in open grassland and more strikes in wooded areas. There was no statistical correlation between rainfall and strike incidence although most properties reported that the number of strikes by C. bezziana was greatest after periods of rain. On a mixed‐breed sheep property in the highlands, Romneys suffered an annual strike rate of 20% compared with 9% in Perendales and 7% in Corriedales. The majority of strikes in sheep were in the vulva and anus region (59% of total). Repeated vulva strike in ewes resulted in reduced fertility such that annual lambing rates were reduced by 66% after three strikes and no lambs were produced after five consecutive strikes. Management practices such as dehorning, castration, tail docking and ear tagging frequently resulted in strikes. Deaths of livestock attributed directly to myiases from C. bezziana infestations were common. The incidence of C. bezziana infestations in wildlife and humans in PNG is documented. The results are discussed in relation to risks of its entry to Australia and potential impact of C. bezziana on the livestock industries and wildlife if C. bezziana was accidentally introduced and became established. The implications of predicted climate change on the potential distribution and hosts in Australia are also examined.