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Home Learn About Sheep Lice Control in Australia Online Learning: Treatment – Pesticide Resistance in Sheep

Online Learning: Treatment – Pesticide Resistance in Sheep

The cost and labour involved in treating for lice is substantial, so it pays to be aware of resistance and to use practices likely to slow its rate of development.

Structured reading

For those who like to see all the information and simply read through it in order. Each heading is a link to a page of information—the note provides a summary of the page.
Tip: Keep this page open and open the links in new tabs.

Resistance, residues and safety—Pesticide resistance
An overview of resistance to lice control chemicals.

Pesticide resistance
About resistance, why it is important, and how it can be slowed.

Question and answer

For those who prefer a problem-based approach to learning, answer the following questions.
Each of the questions below links further down the page to the answers.


  1. What is resistance?
  2. In which chemical groups has resistance been found, in Australia?
  3. Why is it important to know about and slow the development of resistance?
  4. Why is it important to know the group of a lice pesticide?
  5. How can the development of resistance be slowed?
  6. What should you do if resistance is suspected?


You can also click on the link in each answer below to go to LiceBoss pages with related information.

1. What is resistance?

Resistance can be defined as exposure to a low dose of pesticide that enables some lice to survive, and these have genes that may allow them to survive higher doses that would normally kill all lice. Continued use of the same chemical or chemical group allows the resistant lice to survive, breed and increase in numbers until they make up the majority of the population. Read More

2. In which chemical groups has resistance been found, in Australia?

  • Synthetic pyrethroids (SPs)
  • Insect growth regulators (IGRs)
  • Organophosphates (OPs)  — but very rare; only one strain of lice with reduced susceptibility to OPs has been reported, but is not believed to be of any field importance.

Read More

3. Why is it important to know about and slow the development of resistance?

Slowing the spread of resistance helps to control costs by avoiding control breakdowns and the need for extra treatments (extra treatments also increase the level of residues in the wool).

Sometimes, when resistance is present, treatment suppresses lice, but does not completely eradicate them. These suppressed infestations are difficult to detect and increase the chance of lice spreading between flocks, particularly on purchased or agisted sheep.

Preserving the efficacy of currently available compounds is also important as the costs of developing and registering new products continues to increase. New groups of lousicides are almost always more expensive than their predecessors, in turn increasing production costs for woolgrowers. Read More

4. Why is it important to know the group of a lice pesticide?

Knowing which chemical group your lice control products belong to is critical to resistance management—the group is the class of chemical to which the particular active ingredient belongs.

Remember that treatments to prevent flystrike also expose any lice present to pesticides. It is important to use products from different chemical groups when treating for flystrike and lice in the same year and to consider flystrike chemicals when determining a resistance management plan. Fortunately, the two main chemicals used for flystrike control, cyromazine and dicyclanil, do not have any effect against lice and will not contribute to selection for resistance in lice.

It is therefore important to rotate between chemical groups when sheep are treated more than once in a year (long wool treatment followed by off-shears treatment), and ideally, to rotate between effective chemical groups in consecutive years. Read More

5. How can the development of resistance be slowed?

  • Make sure the dose rate is correct
  • Apply chemicals strictly according to label directions
  • Don’t expose treated sheep to untreated lousy sheep
  • Rotate products from different chemical groups
  • Consider which flystrike chemicals are also used
  • Avoid using long wool topical treatments where possible
  • Where a long wool treatment has been used, ensure that a chemical from a different group is used after the next shearing

Read More

6. What should you do if resistance is suspected?

  • Carry out a complete review of your lice control program, including the treatment method used and the biosecurity program. The Treatment Factors Tool and Short Wool Tool in LiceBoss Tools can assist with this.
  • If a long wool treatment is being contemplated, consult the LiceBoss Long Wool Tool to determine whether it is economically justified and which chemicals can be used.
  • Oral fluralaner may be a good option for long wool, as it can eradicate lice from sheep with any length of wool
  • If applying a long wool treatment, use a product from a different chemical group to the last treatment used on this mob.
  • If a long wool treatment is used, it will not eradicate lice (the exception is fluralaner); all sheep will need to be treated after their next shearing. Use a chemical from a different group for the post-shearing treatment.
  • If problems continue to arise and no reason can be identified, seek professional advice.

Read More

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