It’s time to take a stand against resistant sheep lice - Elders Rural Services

It’s time to take a stand against resistant sheep lice

Animal health advisors are urged to encourage sheep and wool producers to adopt effective rotation programs to maintain the efficacy of all available sheep lousicides.

While producers have access to almost 20 off-shears lousicides, these products belong to just four chemical classes with different modes of action: neonicotinoids (e.g. imidacloprid, thiacloprid), spinosyns (e.g. spinosad), macrocyclic lactones (MLs) (e.g. abamectin) and organophosphates (e.g. temephos, diazinon).

Elanco Australasia Senior Brand Manager, Dr Kathryn Humphries, says resistance can develop to any chemical if it is used continuously.

“Using the same product every year means sheep lice populations are potentially being repeatedly exposed to the same mode of action,” she says.

“Just as there is resistance to some drenches and blowfly preventatives, history has shown that resistance can – and will – develop to sheep lousicides.”

Dr Humphries says the continual use of neonicotinoids and spinosyn for off-shears lice control is of particular concern.

“Products containing neonicotinoids and spinosyn account for nearly 70 percent of all off-shears treatments,” she says.

“The potential development of resistance to neonicotinoids or spinosyn would increase selection pressure for resistance to the other, placing both modes of action at risk.”

Industry guidelines discourage the consecutive use of lousicides with the same mode of action or the use of the same mode of action for lice control and flystrike prevention in the same season.1

If consecutive use of the same mode of action is required for lice control, careful attention should be paid to achieving eradication after treatment to help prevent the establishment of a resistant lice population.

“Australian sheep and wool producers have relied upon Avenge® and Extinosad™ Pour-On for the last decade as their ‘go-to’ lousicides. Now it is time to establish a rotation regime to protect these molecules from the development of potential resistance,” Kathryn says.

“Producers who have been using Extinosad Pour-On should consider rotating to Viper®, while producers who have been using neonicotinoids, MLs or organophosphates should consider rotating to Extinosad Pour-On.”

Viper is registered for application to shorn sheep up to seven days after shearing or to unshorn lambs from two weeks to two months of age.

“Viper is the only pour-on lousicide that contains thiacloprid, second-generation neonicotinoid chemistry that is up to six times more potent 234 against sheep lice than imidacloprid,” Kathryn says.

“Using a more potent active ingredient will help to ensure optimal lice control and reduce resistance selection pressure on neonicotinoid chemistry.

“Viper provides rapid knockdown3 control of neonicotinoid susceptible and IGR resistant strains of sheep body lice.

“It continues to kill adult lice and emerging nymphs that hatch from eggs for four weeks after treatment, when applied within 24 hours of shearing.”

Viper is a low odour, low viscosity and suspensible formulation that is easy to apply with the recommended applicator and clean up after use.

It incorporates Lano-Lock® formulation technology for optimal dose delivery and distribution around the sheep’s body.

Dr Humphries says Extinosad Pour-On is an ideal rotation partner for neonicotinoids, MLs or organophosphates.

“Its unique mode of action5 provides robust knockdown control6 of lice with minimal impact on your management or marketing options,” she says.

“Extinosad Pour-On can be applied up to seven days off-shears, to unshorn suckling lambs or to long wool sheep with more than six months wool growth.

“It has no wool withholding period in all usage situations and a relatively short export slaughter interval of 21 days when applied off-shears or to unshorn suckling lambs.”

Elanco guarantees sheep will be lice-free six months after Extinosad Pour-On is applied off-shears when applied in accordance with label directions.*

Extinosad Pour-On has an odourless, water-based formulation that poses minimal risk to livestock, shearers, farm workers or the environment, when used as directed. It is an “allowable input” in Organic programmes certified by Australian Certified Organic.

Remember to always read and follow the label directions. Good agricultural practice is essential for optimal lice control.

*Visit for terms and conditions. References:
1. James, P. (2013). Preventing resistance in sheep lice, (AWI, Sheep CRC).
2. BAH Laboratory Study 6106008 2006.
3. BAH Laboratory Study 6108010 2008.
4. BAH Laboratory Study 6105020 2005.
5. Cisneros, J. et al. (2002). Toxic effects of spinosad on predatory insects. Biological Control. 23:156-163.
6. Levot, G. (2008). Speed of action and in vitro efficacy of spinosad against sheep body lice, Bovicola ovis, resistant to pyrethroid, organophosphate or insect growth regulator insecticides. Aust J. Ent. 47:251-255.
®Registered trademarks. Elanco, Extinosad™ and the diagonal bar logo are trademarks of Elanco or its affiliates. ©2021 Elanco or its affiliates. PM-AU-21-0018. EAH20552

Article written by Elanco for the Autumn 2021 edition of Seasons Magazine. 

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