SHEEP LICE - CONTROL AND INSECTICIDE RESISTANCE

September 2009

Garry Levot

SHEEP LICESHEEP LICEECONOMIC LOSSECONOMIC LOSS -- $123million PA$123million PA

Lost production:Lost production:

* lousy sheep cut about 10% less wool* lousy sheep cut about 10% less wool

(up to $12/head for fine wool!)(up to $12/head for fine wool!)

* cotted wool is worth about 10% less* cotted wool is worth about 10% less

•• decreased tensile strengthdecreased tensile strength

•• yellow d scolouration of wool yellow discolouration of wool

•• Cockle Cockle devalues hidesdevalues hides

•• increased susceptibility to flystrikeincreased susceptibility to flystrike

2mm

BovicolaBovicola ovisovis

SHEEP LICESHEEP LICE• Opportunities to eliminate lice from individual sheep are ‘off-shears’ (0-24h after shearing) ORin ‘short wool’ (1-42 days after shearing).

• Treatments applied at other times may reduce lice numbers to the extent that fleece damage is arrested but will not eliminate theinfestation.

SHEEP LICESHEEP LICE REGISTERED INSECTICIDES:REGISTERED INSECTICIDES:

•• PyrethroidsPyrethroids ((cypermethrincypermethrin, , deltamethrindeltamethrin, , alphamethrinalphamethrin) ) (pour(pour--onsonsand sprayand spray--on)on)

•• Organophosphates (Organophosphates (temephostemephos(dip),(dip), diazinondiazinon (spray(spray--on, dip on, dip under APVMA permit))under APVMA permit))

•• BenzoylphenylBenzoylphenylurea (urea (IGRsIGRs) () (triflumurontriflumuron (pour(pour--on),on),

diflubenzurondiflubenzuron) ) (dip pour(dip and pour--on)on)

•• IvermectinIvermectin (jetting (jetting fluid)

•• Magnesium fluorosilicate/sulphur Magnesium fluorosilicate/sulphur (dip) (dip) –– approved for organicsapproved for organics

•• SpinosadSpinosad(dip and pour(dip and pour--on) on) –– approved for organicsapproved for organics

•• ImidaclopridImidacloprid (pour(pour--on) (soon)on) (soon)

SHEEP LICE SHEEP LICE WHEN THINGS DON’T GO AS PLANNED

CONTROL FAILURE – occurs when a pesticide application does not control a pest as well as expected.

• This may reflect the unrealistic expectations of the producer, failure to apply the product correctly (dose/head and as per label directions), failure to provide adequate prevention from re-infestation post-treatment, or insecticide resistance.

SHEEP LICESHEEP LICEPyrethroid pour-ons introduced in 1981

Failures reported in 1986

SHEEP LICE SHEEP LICE –– pyrethroidpyrethroid resistanceresistance

•• Laboratory diagnosisLaboratory diagnosis

10 fold difference - enough for pour-ons to fail

SHEEP LICE SHEEP LICE –– pyrethroidpyrethroid resistanceresistance

1986 1986 --Low level resistanceLow level resistance•• pourpour--onsons failedfailed

1992 1992 -- HartleyHartley strainstrain• 640+ fold resistance!• pour-ons and dips failed!

Extreme resistance then became increasingly common and widespread

640 fold difference

SHEEP LICE SHEEP LICE –– managingmanagingpyrethroidpyrethroid resistanceresistance

••Resistance to one Resistance to one pyrethroidpyrethroidconferred resistance to them allconferred resistance to them all

•• No crossNo cross--resistance resistance to organophosphatesto organophosphates

HARTLEY

SHEEP LICE SHEEP LICE –– organophosphate resistanceorganophosphate resistance

•• only one only one dia inondiazinon--r si tant resistant popu ation (population (‘‘ rangeOrange’’ found) found

• for resistance managementnote the susceptibility of the note the susceptibility of the ‘‘ OrangeOrange’’ strain to strain to pyrethroidspyrethroidsand the susceptibility of the and the susceptibility of the ‘‘ HartleyHartley ’’ strain to strain to diazinondiazinon

SHEEP LICE SHEEP LICE –– IGR resistanceIGR resistanceAIM: To develop a laboratory test capable of measuring the susceptibility of lice populations to diflubenzuron with a view to diagnosing resistance if it exists.

Normal cuticle Chitin deficient cuticle – note the thin band of normal cuticle

SHEEP LICE SHEEP LICE –– IGR resistanceIGR resistanceHYPOTHESIS: That if they exist, ‘IGR-resistant’ female lice would be capable of laying eggs that would hatch, following treatment with doses of diflubenzuron that prevent hatching of eggs laid by ‘susceptible’ females.

Experiment: 40-50 female lice were treated with 0.2 µL of diflubenzuronsolution, provided with wool and adequate food and kept under ideal conditions in the company of males. Egg laying and hatching was monitored over 19 days.

SHEEP LICESHEEP LICE

Eggs Adult louse

Immature lice -‘nymphs ’ hatch after 10 days @ 37oC

SHEEP LICE SHEEP LICE –– IGR resistanceIGR resistance

0660.05

0520.025

12570.0125

14590.0063

26580.0031

40600.00156

3658Control

Number of nymphs hatched by Day 19

Number of adult lice still alive at Day 19

Diflubenzuron dose(µg per louse)

IGR-susceptible’ – Claremont strain (low-range pyrethroid resistance/IGR naive)

SHEEP LICE SHEEP LICE –– IGR resistanceIGR resistance

IGR-susceptible’ - Hartley strain (highly pyrethroid resistant/IGR naive)

0180.10

0200.05

0150.025

6350.0125

4240.0063

9330.0031

8300.00156

1944Control (acetone)

Number of nymphs hatched by Day 24

Number of adult lice still alive at Day 24

Diflubenzurondose

(µg per louse)

SHEEP LICE SHEEP LICE –– IGR resistanceIGR resistance

IGR Field Failure: Stanthorpe (Qld) strain

22490.20

17430.10

17190.05

18400.025

8150.0125

1330.0063

26370.0031

11180.00156

1425Control (acetone)

Number of nymphs hatched

by Day 19

Number of adult lice still alive at

Day 19

Diflubenzurondose

(µg per louse)

SHEEP LICE SHEEP LICE –– IGR resistanceIGR resistance

RESISTANCE IS REAL!RESISTANCE IS REAL!• complaints common

• no distinctive regional distribution (NSW/Qld/WA/Vic)

• tell-tale signs are immature lice on treated sheep

• history of repeated use of IGRs for lice and/or blowflies

• labels now refer to ‘susceptible’ strains

• will become more common if IGRs continued to be used

ACKNOWLEDGEMENTS•Funding for this project was provided by Australian wool producers and the Australian Government through Australian Wool Innovation.

• IGR resistance bioassays - Narelle Sales