Strategic fly control in sheep

Economic impact of blowfly strike in New Zealand. 

Economic impact of blowfly strike 

Blowfly strike is the second most costly parasitic disease of sheep in New Zealand, ranking only behind gastro-intestinal roundworms in economic importance. ¹ Research has shown that even relatively small strikes can cause a marked loss of appetite in the struck animal, resulting in weight loss.² 

Anecdotal evidence suggests that ewes and ewe hoggets struck in late summer/autumn are far less likely to get in lamb than non-struck animals. 

In addition, farmers are legally required to protect their stock against blowflies. 

Preventing blowfly strike 

Four species of blowfly are recorded as initiating strikes on sheep in New Zealand, with the Australian green blowfly (Lucilia cuprina) and the European green blowfly (Lucilia sericata) recognised as the most important species.   

Prevention of blowfly strike caused by the larvae of these species is largely reliant upon application of insecticides by a variety of means (e.g. saturation dipping, jetting, low volume pour-ons or spray-ons) to the fleece of at-risk animals.  

Most blowfly strike preventative products belong to the insect growth regulator (IGR) group of chemicals. In turn, IGRs can be divided into two distinct chemical classes based on their different and unrelatedmodes of action:

Blowfly resistance to treatments 

Lucilia spp. blowflies have a remarkable ability to develop resistance to various chemicals used to control or prevent flystrike. Resistance is first shown as a shorter than expected period of protection, even if the product is correctly applied at the right dosage.  

Strains of L. cuprina and L. sericata resistant to diazinon, an organophosphate, have been recorded throughout New Zealand.³ Resistance by Lucilia cuprina to diflubenzuron was confirmed in Australia in 2002 with cross-resistance to diazinon identified as a factor in its development.⁴ The registration of diflubenzuron for the prevention of blowfly strike in sheep in Australia was voluntarily removed in 2008.  

A large study run in 2010-11 confirmed the presence of triflumuron resistant European Green Blowflies^5. in New Zealand, most particularly in North Western regions of the North Island. 

Strains of the Australian Green Blowfly (Lucillia cuprina) resistant to cyromazine and dicyclanil have been identified in Australia ⁷, with the resistance appearing as a reduced protection period. This resistance has not yet been identified in New Zealand; however Elanco NZ have set up a resistance testing service as part of any adverse event investigations looking at loss of expected efficacy of blowfly strike protection products. 

Blowfly resistance management guidelines  

Minimising the losses caused by blowfly strike requires a planned preventative treatment approach using effective products applied at the correct time.  

Resistance management also needs to be factored in when planning blowfly strike prevention programs, with sheep farmers needing to recognise that flies could develop resistance to any chemical. 

Recommendations for resistance management of sheep ectoparasites in New Zealand are in their infancy, however, the Australian sheep industry has well-established blowfly strike and lice control strategies that should be considered for use in New Zealand.⁶  

A key recommendation is to manage blowfly strike and lice as separate issues.  

Each parasite should be treated with an effective product at the appropriate time. In many cases, this strategy will involve the use of different products and application methods at different times of the year. 

Another important recommendation is that products should be applied as closely as possible to label guidelines. For all products including CLiK, CLiKZiN and Cyrex Liquid, a shorter period of protection may occur if they applied incorrectly, if there is excessive fleece soiling or if wool infections such as mycotic dermatitis (fleece rot) are present. Heavy rain following application of this product may also diminish the period of protection against flystrike. 

Key Points 

CLiK™ Extra  

New Zealand sheep farmers wanting “peace of mind“ blowfly protection have relied on CLiK™ Spray-On to provide long term protection (10–18 weeks) against blowfly strike for over 20 years. CLiK Extra sets an even higher benchmark by protecting sheep from flystrike for 14-26 weeks in a single application. 

CLiK Extra contains 30% extra dicyclanil, the same proven active ingredient in CLiK Spray-On. Dicyclanil is an extremely potent insect growth regulator that interrupts the lifecycle of blowflies. It prevents emerging larvae from moulting into damaging second stage maggots, thereby preventing flystrike.  

CLiK Extra protects against blowfly strike for 14 to 26 weeks, as well as protecting docking wounds against flystrike.  

CLiK Extra gives you extra peace of mind that your sheep have the longest protection available against flystrike, particularly with unpredictable fly seasons. 

Trusted solutions and advice from Elanco   

Elanco is an industry leader in sheep blowfly solutions with a product range including CLiK^™   Extra Spray-On, CLiK Spray-On, CLiKZiN™ Spray-On, Extinosad^™ and ExPO Extinosad Pour On coupled with benchmark technical support and customer service. For any information or technical advice on managing sheep lice, contact Elanco Customer Service 0800446121 

Registered indications: CLiK Extra Spray-On contains 65 g/L dicyclanil. CLiK Extra is registered for the protection of sheep, with > 4 weeks wool growth against fly strike caused by dicyclanil-susceptible strains of blowflies, including the Australian Green Blowfly (Lucilia cuprina) for 14 to 26 weeks and for the protection of docking wounds on sheep against fly strike caused by dicyclanil-susceptible strains of blowflies, including the Australian Green Blowfly (Lucilia cuprina) during the wound healing process.