Blowfly resistance management and prevention of flystrike

Australian sheep blowfly
Lucilia cuprina is resistant to
some flystrike prevention chemicals.

A.C.G. Heath
AgResearch Wallaceville, PO Box 40063, Upper Hutt

(Updated March 2003)

Reason for strategy

Both the Australian sheep blowfly, Lucilia cuprina, and its European counterpart, L. sericata, are resistant to some insecticide groups used in the prevention of flystrike in New Zealand sheep (Wilson 1999). Management strategies aimed at reducing reliance on insecticides will not only conserve the efficacy of existing products, but will help reduce residues in wool to levels that are acceptable to overseas markets.


Individuals of the Australian sheep blowfly, Lucilia cuprina, that are thought to have entered New Zealand in the late 1970s, carried alleles that conferred resistance against diazinon, an organophosphate insecticide (Arnold & Whitten 1976; Wilson & Heath 1994), the basis of resistance being a microsomal esterase E3 (Hughes & Raftos 1985). Many years before, in Australia, L. cuprina had demonstrated resistance to cyclodienes and carbamates (Shanahan 1959; Hughes & McKenzie 1987). In New Zealand, L. sericata, a blowfly responsible for flystrike from the early days of sheep farming in this country had also shown cyclodiene resistance (Hart 1961). More recently, some populations of L. cuprina showed altered susceptibility to formulations containing benzoyl ureas, and L. sericata is demonstrating more widespread organophosphate resistance than previously (Kotze et al. 1997; Haack et al. 1999; Wilson 1999).

Flystrike (ovine myiasis) is a disease of livestock caused in New Zealand by four species of blowflies (Calliphoridae), either individually or in concert (Heath & Bishop 1995). Both L. cuprina and L. sericata are responsible for initiating the majority of flystrikes, but the primary lesion is often colonised a little later by either Calliphora stygia, the brown blowfly, or Chrysomya rufifacies, the hairy maggot fly. Both of these latter species alone can also initiate flystrike. Sheep affected with flystrike can suffer a variety of symptoms ranging from weight loss to death. Survivors lose wool and pelt quality as well (Heath 1994).

The principal means of preventing flystrike has always been dipping, which saturates the entire sheep's fleece, or body regions most prone to flystrike, in an insecticidal formulation that persists for long enough to provide the farmer with a worry-free period during times of high blowfly activity.

Because dipping sheep is not a straightforward or cheap procedure, farmers often use insecticides that combine flystrike prevention with louse control in one operation. This means that selection pressure for resistance can operate on both parasites simultaneously (Sales et al. 1996), which is not a desirable outcome.

Current status of blowfly insecticide resistance in New Zealand

Diazinon-resistant populations of L. cuprina and L. sericata occur throughout New Zealand (Wilson 1999) and have weak side resistance to other organophosphates. The result is that protection periods afforded against flystrike are substantially shorter (ca 75% less) than might otherwise be expected (Levot & Boreham 1995). There is also a degree of resistance to the benzoyl urea diflubenzuron in some populations of L. cuprina that seems to be directly correlated with diazinon resistance (Haack et al. 1999). There have been no reports of altered susceptibility to other chemical groups currently in use as flystrike preventives.

Resistance management and prevention strategy

There is no recorded resistance to triazines, pyrimidine carbonitriles or macrocyclic lactones among blowflies in New Zealand or overseas. These materials can be used in regions where diazinon and diflubenzuron resistance makes flystrike prevention difficult. Alternatively, although there is side resistance to organophosphates other than diazinon, it is not strong, and satisfactory flystrike protection periods can still be achieved using these chemicals.

For farmers wanting to reduce reliance on synthetic insecticides, a range of non-chemical methods available that, if used in an integrated fashion, can reduce flystrike prevalence (Cole & Heath 1999; Edwards et al. 2001). Blowfly trapping and behavioural disruption (Heath & Leathwick 2001), along with parasitoids (Bishop et al. 1996) and specialist forage crops that reduce breech soiling (Leathwick & Heath 2001) can, when used in conjunction with husbandry and grazing management provide flystrike protection, largely independent of chemical use.

Products with label claims for prevention of flystrike in New Zealand

Table 1: Products with label claims for prevention of flystrike in sheep in New Zealand (Nottingham 2003; see also Many of these products have a dual purpose and are used to control sheep body-louse, Bovicola ovis, as well, whereas others have even wider claims that include many ectoparasites of sheep. These label claims are not shown here. Method of application varies with products and is shown for each as the choice of high versus low volume can be relevant in resistance management and environmental protection.
Pesticide category
and IRAC chemical group
Pesticide common and (product) namesMethod of application
Organophosphate 1B chlorfenvinphos (Supreme) Plunge, shower, jetting
chlorpyrifos (Xterminate 10) Plunge, shower, jetting
coumaphos (Asuntol liquid) Plunge, shower
propetamphos (eNkamphos 500, eNkamphos 1250) Plunge, shower, jetting
Organophosphate/pyrethroid 1B/3 chlorpyrifos/cypermethrin (Flypel) Applicator/spray
Pyrethroid 3 alpha-cypermethrin (Duracide, Vanquish) Pour-on
high cis cypermethrin (Cypor) Applicator/spray
Macrocyclic lactone (avermectin/milbemycin) 6 ivermectin (Jetamec jetting fluid for sheep) Jetting
(Ivomec maximizer CR capsule for lambs, Ivomec maximizer CR capsule for adult sheep)
Ruminal constant release capsule
ivermectin (Erase MPC) Spray/jetting
Benzoyl urea 15 diflubenzuron (Blitz, Ectogard, Fleecemaster, Zenith) Plunge, shower, jetting
triflumuron (Epic ezy pour-on for sheep) Applicator
triflumuron (Zapp, Zapp jetting liquid) Applicator/spray, jetting
Triazine 17 cyromazine
(Cyrazin liquid, Vetrazin liquid, Cyro-fly 500 dip and jetting fluid)1
Plunge, shower, jetting
(Cyrazin spray-on, Vetrazin spray-on, Cyro-fly 60 spray-on)1
Pyrimidine carbonitrile unclassified dicyclanil (Clik)1 Applicator/spray
Spinosyn 5 spinosad (Extinosad) Plunge, shower, jetting

1For flystrike prevention only, no biting-louse claim.

Note: Control failure does not always imply resistance

The following guidelines are recommended:


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Bishop DM, Heath ACG, Haack NA 1996. Distribution, prevalence and host associations of Hymenoptera parasitic on Calliphoridae occurring in flystrike in New Zealand. Medical and Veterinary Entomology 10: 365-370.

Cole DJW, Heath ACG 1999. Progress towards development and adoption of integrated management systems against flystrike and lice in sheep. Proceedings of the New Zealand Grassland Association 61: 37-42.

Edwards S, Marshall A, Cole D, Heath ACG 2001. Fly and Lice, Numbering their Days. WoolPro, Wellington, New Zealand. 52 p.

Haack NA, Heath ACG, McArthur MJ 1999. A preliminary survey of tolerance to diflubenzuron in the blowflies Lucilia cuprina and L. sericata in New Zealand. New Zealand Journal of Zoology 26: 81(Abstract).

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Heath ACG, Bishop DM 1995. Flystrike in New Zealand. Surveillance 22: 11-13.

Heath ACG, Leathwick DM 2001. Blowfly traps and prevention of flystrike: a review of the New Zealand experience. Proceedings of the FLICS Conference, Launceston, Tasmania, June 2001: 273-278.

Hughes PB, McKenzie JA 1987. Insecticide resistance in the Australian sheep blowfly, Lucilia cuprina: speculation, science and strategies. In: Combating Resistance to Xenobiotics. Ford MG, Holloman DM, Khambay BPS, Sawicki RM ed. Ellis Horwood, Chichester. Pp. 162-177.

Hughes PB, Raftos DA 1985. Genetics of an esterase associated with resistance to organophosphorus insecticides in the sheep blowfly, Lucilia cuprina (Wiedmann) (Diptera: Calliphoridae). Bulletin of Entomological Research 75: 535-544.

IVS Annual 2005.

Kotze AC, Sales N, Barchia IM 1997. Diflubenzuron tolerance associated with monooxygenase activity in field strain larvae of the Australian sheep blowfly (Diptera: Calliphoridae). Journal of Economic Entomology 90: 15-20.

Leathwick DM, Heath ACG 2001. Specialist forages-a role in flystrike management? Proceedings of the FLICS Conference, Launceston, Tasmania: 374-379.

Levot GW, Boreham PFL 1995. Resistance and control of sheep ectoparasites. International Journal for Parasitology 25: 1355-1362.

Nottingham R ed. 2003. IVS Manual 2003, Volume 18. MediMedia, Auckland, New Zealand. (See also

Sales N, Shivas M, Levot G 1996. Toxicological and oviposition suppression responses of field populations of the Australian sheep blowfly, Lucilia cuprina (Wiedmann) (Diptera: Calliphoridae) to the pyrethroid cypermethrin. Australian Journal of Entomology 35: 285-288.

Shanahan GJ 1959. Genetics of resistance to dieldrin in Lucilia cuprina Wiedmann. Nature 186: 181.

Wilson JA 1999. Aspects of insecticide resistance in New Zealand strains of the sheep blowflies, Lucilia cuprina and Lucilia sericata. PhD thesis, Victoria University of Wellington, New Zealand. 467 p.

Wilson JA, Heath ACG 1994. Resistance to two organophosphorus insecticides in New Zealand populations of the Australian sheep blowfly, Lucilia cuprina. Medical and Veterinary Entomology 8: 231-237.